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From the collection of the 


i a 


San Francisco, California 




Volume XXXII January, 1939 


Undersea Cinematography E. R. F. JOHNSON 3 

The Road Ahead for Television I. J. KAAR 18 

Report of the Studio Lighting Committee 44 

Photographic Effects in the Feature Production "Topper" 


Latent Image Theory and Its Experimental Application to 
Motion Picture Sound-Film Emulsion W. J. ALBERSHEIM 73 

The Evaluation of Motion Picture Films by Semimicro Testing 


Current Motion Picture Literature 110 

Spring, 1939, Convention '. 113 

Society Announcements 117 




Board of Editors 

J. I. CRABTREE, Chairman 



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Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of 
Motion Picture Engineers, Inc. 

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** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 
** Past-President: S. K. WOLF, RKO Building, New York, N. Y. 
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* Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

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** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio. 

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* Term expires December 31, 1939. 
** Term expires December 31, 1940. 


Summary. The dates of the first recorded use of underwater photography and 
the tendencies toward its increasing use by producers are noted, and the author's 
early experiences in this field are described. For work in natural settings the most 
useful equipment consists of submergible cameras placed on the bottom and operated 
by divers. The problems of and equipment for such work are dealt with and it is 
pointed out that studio tank work shares most of these problems. 

The optical properties of water are described. Since water is less transparent 
than air, photography by natural light is limited to shallow depths and more power 
is required for artificial illumination under water. Since colors are not absorbed 
equally, accurate monochrome rendering and photography in natural color are com- 
plicated. Haze limits the distance at which pictures can be taken under water, but 
is largely confined to a part of the spectrum and can be partially eliminated by the 
use of color filters. It is plane polarized and can, therefore, also be suppressed by 
the use of polarizing plates. The advantages of this method are briefly stated it 
does not distort monochrome rendering and can be used in natural color photography. 

The ideal attributes of equipment for use in underwater cinematography are outlined 
and available equipment is briefly described. 


The first recorded attempt to take photographs under water that 
has come to our attention was by Boutan in 1893 and we understand 
that he succeeded in securing a few fairly successful still pictures. 

The possibilities of underwater motion pictures seem to have in- 
trigued the fancy of commercial producers almost as early, if indeed 
not earlier, than it did the scientists and educators. Williamson 
produced the underwater picture, Twenty Thousand Leagues under the 
Sea, in 1915-16, and at about the same time scientists, among whom 
were Bartsch, Beebe, and Minor, started using water-tight motion 
picture camera housings in conjunction with the suitless type of 
diving helmet, in order to take motion pictures with which to illustrate 
their lectures upon underwater life. 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 3, 

** Mechanical Improvements Corporation, Moorestown, N. J. 


4 E. R. F. JOHNSON [j. s. M. P. E. 

Recently the tendency of producers to show what happens under 
water as a part of their stories has grown vastly, to say nothing of 
pictures having the principal parts of their plots based on action 
allegedly taking place there. Indeed pictures of champion divers or 
swimmers are no longer considered complete without a view of their 
graceful evolutions after penetrating the surface. Some real ocean 
water scenes were used in the excellent story Submarine DI and 
underwater scenes can be used to add to the romantic touch of a 
picture, as was done in Jungle Love. The work of naval and com- 
mercial divers has as yet hardly been touched upon and their heroic 
exploits offer material for a host of future thrillers. People in ever- 
increasing numbers are becoming cognizant of the real underwater 
conditions. For instance, Miami University has a class in marine 
zoology where the students, using diving helmets, go below the sur- 
face. At the Marine Studios in Florida and at the Bermuda Aquarium 
tourists put on diving helmets, or observe the underwater world 
through ports. In France, Paul Painleve's underwater club is edu- 
cating another section of the public. This increasing familiarity 
is making audiences more critical, and the technic and equipment for 
actual underwater photography as contrasted to shots through glass 
port-holes in tanks are of both present and growing importance to 
entertainment pictures, as well as to the scientist and educator. 


The author's vigorous attack on the problems involved in under- 
water photography was brought about by a stinging defeat in 1928. 
We read one of Beebe's glorious descriptions of the beauties of under- 
sea gardens and the complete ease with which they could be visited 
and photographed. An Eyemo camera was enclosed in a simple case 
with a box of calcium chloride to keep the condensation off the lens 
and window. The result of several weeks' work was very mediocre, 
however, for we found out that if one can see forty feet that does not 
mean that he can take good pictures at more than ten, or always 
even up to ten. We found that natural light is strong enough for 
photography under water only between 10 : 30 A.M. and 3 : 30 P.M. in 
the summer and even less in winter ; that the pellucid tropic seas are 
more often than not full of white sand, green algae, gray-green marl, 
or other detritus; and that if the undersea photographer hoped to 
get anything in a natural set he had to be lightning fast to grasp his 


Diving bells and baby submarines were considered, but after 
talking with a few persons who had had experience with such equip- 
ment, we saw that they could not be transported and put into position 
with sufficient ease and speed to suit the underwater photographer, 
and they are the plaything of every wave or squall of wind. We at- 
tached cameras to water telescopes; we shot them through glass- 
bottomed buckets; we submerged them and sighted through peri- 
scopes. But pictures from an unsteady base are unattractive and 
tend to make the audience seasick. It is our opinion, therefore, that 
underwater pictures can best be made from the bottom and not the 
surface ; also, that a compact underwater camera operated by a diver 
should be used for all picture work in the open sea, lakes, and rivers. 
The same applies to a considerable degree also in swimming pools and 
tanks, for the cameraman shooting through a port-hole is greatly 
hampered in following a moving object, and most underwater sub- 
jects depend on action rather than expression to tell their story. 

The physical qualities of water are responsible for many of the 
difficulties encountered in underwater photography. The purest of 
water is far less transparent than air; and, because it is an excellent 
solvent, it is rarely pure in nature; and dissolved matter profoundly 
affects the optical properties. Then, too, water, having greater den- 
sity and viscosity than air, supports a much greater proportion of 
suspended matter both organic and inorganic, and this has an even 
greater effect on its optical properties. The quantity and kind of 
dissolved matter are relatively constant for any location and, at 
least in sea water, are nearly the same for almost all areas where 
underwater pictures can be taken. Suspended matter, on the other 
hand, is highly variable both for different locations and at the same 
location with varying season and weather. It is the quantity of 
suspended organisms and particles that finally determine whether 
or not satisfactory pictures can be taken at a particular place or time. 


In undersea photography it is general practice to use ordinary cine 
lenses computed for use in air protected by a plane window. This 
introduces a water-air boundary which affects the focus and correc- 
tions of the lens. Objects under water appear nearer and larger both 
to the eye and to a camera. We have computed the effect upon focus 
and it turns out that the ratio of the air focus to that under water is 
equal to the index of refraction of air with respect to water. The 



[J. S. M. P. E 

index varies with the salinity and temperature of the water but the 
value 0.750 may be used for all conditions with negligible error. It 
follows that to focus on an object at any distance under water the 
same lens extension is required as for an object at three-quarters of 
that distance in air. 

The presence of the water-air boundary in front of the lens also 
introduces both spherical and chromatic aberration. Fortunately, 
if the plane of the window is perpendicular to the axis of the lens, 
they are both too small to require correction. In tank work any 
attempt to position a camera other than normal to the plane of the 
window will result in objectionable aberration. 

5000 6000 


FIG. 1. Spectral quality of mean noon sunlight at the 
surface, and through 25 and 50 feet of water. 

When photographing by sunlight, the first factor to be considered 
is the overall reduction in intensity of light. This varies greatly with 
conditions, but it is our experience that under average conditions 
twenty-five to thirty-five feet is the limiting depth using rapid lenses 
and Eastman Super X or Agfa Supreme film and a filter with a factor 
of from two to four. The newer ultra-rapid films extend this limit 
somewhat. Fortunately the largest percentage of interesting marine 
life and human activity is to be found within this range. At greater 
depths photographic subjects become more scarce and difficulties are 
materially increased. 

A further complication is added by the fact that water does not 
absorb different colors equally. Fig. 1 shows the approximate inten- 
sity and spectral quality of sunlight at the surface and at several 
depths in water. The curves were computed from the laboratory 

Jan., 1939] 


measurements of the transparency of sea water by E. O. Hulbert 1 and 
approximate the conditions found in practice. It will be seen that 
sea water is most transparent in the blue-green region between 4400 
and 5400 A and that the red is quickly absorbed. This filtering ac- 
tion of water makes difficult a true monochrome rendering of subjects, 
and has an even greater effect on photography in natural colors. In 
color photography compensating filters can be used to correct for 
the spectral quality of the light at any given depth. It is to be noted, 
however, that theoretically a different filter would be required for 
every depth. Moreover, the same would be true for different dis- 
tances from the camera to the object. Thus, if an object at six feet 




4500 5000 


FIG. 2. Spectral distribution of water haze in sea water; 
transmission curve of Wratten Aero No. 2 filter. 

from the camera and six feet deep is being photographed, a compen- 
sating filter correct for twelve feet of water would be required. How- 
ever, even though filters are used objects closer than six feet would 
tend to be too red and at greater than six feet would be progressively 
greener the background fading out in a uniform blue-green. This, 
in fact, is a real effect. Objects at a distance do not appear to be the 
same color to a diver as when they are close by. A diver's vision 
fades out in a misty blue-green haze. Color-film, however, accen- 
tuates this effect, making the background an unnaturally intense 
blue-green. We have taken both Kodachrome and Duf ay color stills 
and Dufaycolor motion pictures, most of which exhibit this effect. 
By proper limitation of depth and distance, however, beautiful 
results can be obtained. 

8 E. R. F. JOHNSON [J. S. M. P. E. 

The greatest bete noire of the underwater photographer is water 
haze or "nuisance light." It is strictly analogous to aerial haze but 
being much more intense its effect shows up in the picture of an ob- 
ject only a few feet away rather than a matter of miles. This haze 
originates in the scattering of light by the water and by dissolved and 
suspended matter between the camera and the object. Its effect is to 
cause a uniform exposure over the whole picture, which tends to mask 
detail and contrast; as the distance becomes greater the haze becomes 
brighter, compared to the brightness of the object, finally masking it 

It was felt that water haze, like aerial haze, should consist prin- 
cipally of light in a limited spectral region and that a color filter 
would eliminate much of it. With this in mind we conducted a 
series of experiments with an underwater spectrograph. Fig. 2 
gives the relative spectral distribution of the haze light in the sea 
water off the Florida Keys. 2 Tank tests with distilled water gave 
an almost identical curve. Camera tests showed a great improve- 
ment when a Wratten Aero No. 2 filter was used. The transmission 
curve of this filter is also given. Fig. 3 shows the improvement 
obtained by the use of filters : (a) is a scene at a distance of six feet 
with no filter; (b) a similar scene using an Aero No. 2; and (c) with 
a Wratten No. 25 filter, which transmits only the red rays of wave- 
lengths greater than 6000 A. This last picture shows only very 
slight improvement in detail over the one taken with the Aero No. 2, 
and this improvement is more than offset by the unnatural appear- 
ance of the subjects and by the extreme exposure increase required. 
The chief objection to the use of color filters to eliminate haze is the 
fact that water is most transparent to the blue-green region of 
the spectrum ; but this is also the region of maximum intensity of the 
haze light, so in eliminating it the most efficient photographic light 
is also lost. Fortunately there is another means of cutting out this 
troublesome haze. 

So far as haze light is concerned studio tank work offers the same 
problems as natural settings as we believe at least one producer has 
found, to his sorrow, after putting several thousand gallons of expen- 
sive distilled water into a nicely scrubbed tank and then failing to get 
the clear crisp pictures he wanted so badly. 

The fact that this nuisance light is present even in distilled water 
that has stood long enough to be free of air bubbles indicates that 
the origin of much of it must be molecular scattering by the water it- 

Jan., 1939] 


FIG. 3. Use of color filters to reduce water 
haze; (a) no filter. (6) Wratten Aero No. 2 
.filter, (e) Wratten No. 25 filter. 

10 E. R. F. JOHNSON [j. s. M. P. E. 

self. Therefore, according to the Raman-Einstein-Smolchowski 
theory it should be almost completely plane polarized. 3 Our dis- 
covery of this fact led to our use of polarizing screens. By the use of 
these screens it is possible to eliminate a greater part of the "nuisance 
light" than by any other means. Their use requires an exposure in- 
crease of from two to four times. Unfortunately, the haze light is not 
completely polarized, so, while the distance at which satisfactory 
pictures can be obtained is extended, there is still a very definite limit. 

Probably the most advantageous feature of this method of elimi- 
nating haze light is that polarizing screens are almost perfectly spec- 
trally neutral. They do not distort the monochrome rendering nor 
do they eliminate the most useful portion of the spectrum as does a 
yellow or red filter. This spectral neutrality further makes possible 
haze elimination when using color-film. However, at present the 
speed of color-film does not permit the use of both a compensating 
filter and a polarizing plate under normal conditions. If the speed 
of these materials can be doubled a great improvement in the quality 
of undersea color pictures is anticipated by the use of polarizing 

Light-rays passing into water through the surface are bent until 
they travel nearly straight down, so by natural illumination subjects 
under water are inclined to be overly contrasty with highlights on top 
and densely shadowed undersides. We tried relieving this situation 
with reflector boards but found that boards large enough to help at 
all had so much water resistance that even in slack water they were 
difficult to handle and with any current it became impracticable 
either to set them or keep them in position. Shadows can be re- 
lieved to a certain extent by the use of artificial lights. Reflectors 
must be small and highly efficient or they become unmanageable in 
any current. In using lights, it is necessary to exercise extreme care 
in placement, otherwise haze light makes the lamp beam visible. 
Since most of the energy from incandescent lights is in the red end of 
the spectrum, in which region the water has its strongest absorption, 
the power requirements are much greater than for equivalent illumina- 
tion at the surface. 


Having outlined the technical and practical difficulties confronting 
the underwater cinematographer we shall now briefly describe the 
ideal attributes of apparatus to meet these difficulties and the prac- 
tical equipment developed by/our company, for this specialized field. 


Motion picture producers early learned that dependence upon na- 
tural light could be extremely expensive, sometimes tying up the 
whole staff of actors and technicians for days waiting for favorable 
conditions. In underwater photography the clarity of the water 
and the size of the waves are also factors that can vary independently 
of sunlight, thus further limiting the useful part of time on location. 
Moreover, even under the best of conditions, the working day under 
sea is shorter than at the surface; first, because the sun reaches full 
brightness later and fades earlier; and, second, long exposure to water 
soon tires both cameramen and actors. These factors tend to run up 
the expense of underwater footage and demand a high standard of re- 
liability, convenience, and speed of operation in the apparatus used. 

Sending equipment to the surface for adjustments of stop or focus 
or change of filter is wasteful of time. It is, therefore, the first re- 
quirement of underwater equipment that the controls for all adjust- 
ments be quickly and conveniently operable under sea by the diver. 

The fact that water is a far less yielding medium than air dictates 
other requirements. A camera that would be quite stable in a 
twenty-mile wind might easily be thrown over by even a two-mile 
current. When working at small depths the under-surface surge 
from waves tends to sway and billow both diver and equipment. 
Very often the diver has difficulty in standing or walking even with- 
out apparatus. Therefore, tripod mount and spring or electric motor 
drive are essential. Apparatus must be compact to keep down its 
water resistance; it must be light enough for ease in carrying, yet 
heavy enough to be stable. All connections must be rigid. 

When under water, man becomes a clumsy, slow-moving creature. 
It is, therefore, important that any couplings that must be made 
should be large and simple. Calibration markings should be large 
and distinct, and all controls and calibrations should be visible 
and operable from one position. 

Even after short submergence the skin of a diver's hands becomes 
softened and very easily cut by things that would not do so at the sur- 
face. For this reason everything must be smooth with no sharp 

The construction of diving helmets, and the fact that the camera- 
man has difficulty in remaining perfectly still, make it necessary that 
view-finders be corrected for an eye position well back of the port, and, 
further, the reduced illumination makes important a large brilliant 


E. R. F. JOHNSON [J. S. M. p. E. 

FIG. 4. Professional model underwater motion picture camera. 

FIG. 5. Underwater housing for Bell & Howell Eyemo, open for loading. 

Jan., 1939] UNDEkSEA ClNEMAtOGkAPfiY "13 

Direct focusing is a difficult if not impossible task and therefore 
accurate focus calibration of lenses is a necessity. 

In developing apparatus for underwater cinematography we have 
not undertaken the design of new camera mechanisms but rather have 
modified for underwater use the excellent existing surface equip- 
ment. The materials and construction of all apparatus are such that 
no condensation occurs on windows when submerged, thus eliminating 
the need of troublesome and time-consuming chemical driers. In 
general, it may be said that any surface camera can be encased for 
such use, but for our standard models we have selected those whose 
size and layout make them most adaptable for the purpose. 

FIG. 6. Professional model underwater still camera. 

The most complete unit is the professional model motion picture 
camera, Fig. 4, which was designed to give the underwater cinema- 
tographer an instrument possessed of the greatest possible flexibility 
and convenience of operation. 

The camera mechanism is the Akeley, with a capacity of 200 feet of 
standard 35-mm. motion picture film. It is driven by an electric 
motor with external speed control. The trigger switch is in a sepa- 
rate water-tight case mounted on the cable; it may be used at a short 
distance from the camera or mounted on the guiding handle of the 
tripod, making it possible to guide and run the camera with the left 
hand, leaving the right hand free to adjust focus and aperture. A 

14 E. R. F. JOHNSON [j. s. M. P. E. 

Veeder type of footage counter is at the rear of the case, and every two 
feet a dim light flashes at one side of the view-finder, permitting the 
cameraman to keep count of footage without looking away from the 
scene. Three lenses, wide-angle, standard, and telephoto, are 
mounted in the instrument. These are in a vertical row rather than 
in the conventional turret, in the interest of simpler lens and filter 
control. Provision is made for two color niters, which may be thrown 
in or out at will, and a polarizing plate which may be racked in front 
of the lens or removed. It may also be rotated under water and a 
sun's position indicator on the rear of the camera indicates the proper 
rotation when using natural light. 

The view-finder gives a large brilliant image and incorporates ad- 
justment for correction of parallax. Supplementary lenses are used 

to obtain the fields of the dif- 
ferent camera lenses without 
a reduction in the image size. 

In air the camera weighs 
approximately seventy-five 
pounds but submerged only 
twenty-five, which makes it an 
easy load for a single diver. 
The water-tight covers of the 
camera and lens compartments 

FIG ' 7 ' nd hngf rWeS ' are ga^keted and held fast by 

quick-acting latches which re- 
quire no tools to operate and make loading an extremely rapid opera- 
tion. All controls are clearly calibrated and visible from the operat- 
ing position. The diver-cameraman can accomplish all adjustments 
under water with the exception, of course, of reloading. 

We have also a housing for the Bell & Howell Eyemo, Fig. 5. In 
this case the camera is removable from the water-tight case. The only 
permanent alteration is the addition of fittings to the lenses which 
in no way interfere with the ordinary use of the camera in air. The 
case will accommodate any of the standard Eyemo lenses up to the 
3 3 / 4 -inch focal length. Lenses can not, however, be changed under 
water. Provision is made for the underwater adjustment of lens 
focus and aperture, for winding of the spring motor, and operation of 
the trigger. All controls are visible and adjustable from the rear of 
the camera. There is a single large case opening which is gasketed 
and held by quick-acting latches, and it is not necessary to remove 

Jan., 1939] 



the camera from the housing which reduces to a minimum the time 
required to load or change lenses and niters. 

There is also available a professional model still camera, Fig. 6, 
which, because it uses standard 35-mm. motion picture film, can be 

FIG. 8. Underwater range-finder. 

used for taking check stills of motion picture scenes as well as for or- 
dinary still pictures. This instrument makes use of the Leica camera 
mechanism, and all controls can be operated by the diver more con- 
veniently than in the average air 
camera. It is necessary to take it 
to the surface only for film reloading. 
It weighs in air approximately twenty- 
four pounds and submerged, about 
ten. There is an underwater choice 
of no filter, either one of two color 
filters, a polarizing plate, or combina- 
tion of filter and polarizing plate. 
There is also provided an indicator 
for determining the proper degree of 
rotation for the polarizing plate. A 
large brilliant-image field-finder is in- 
corporated in the camera as well as a 
built-in range-finder coupled to the 
camera lens in the. interest of rapid 

"For determining the correct exposure 
under water, which is essential as the 
light available varies greatly both in 
amount and color with, differences in depth, the amount and kind of 
impurities present, arid the condition of the water surface, there, is a 

PIG. 9. Underwater lamp. 

16 E. R. F. JOHNSON [j. s. M. P. E. 

substantial water-tight housing for a Weston model 650 exposure- 
meter, Fig. 7. 

Accurate measurement of distance is also necessary. Under most 
conditions illumination is relatively weak and aperture settings must 
be large, resulting in short focal depth. Under water the eye is a very 
poor judge of distance and yardstick measurements are often difficult. 
To make quick accurate measurements possible an underwater range- 
finder has been developed, Fig. 8. It is of the double-image type, 
different from the conventional instrument only in the increased 
size of the optical parts and in the calibration which gives true dis- 
tances under water. 

FIG. 10. Amateur underwater still camera. 

For supplementing natural light there are special underwater 
lamps (Fig. 9) using corrosion-resistant reflectors, which for ease of 
handling in underwater currents are of comparatively small size. 
Special diving lamps as well as standard photofiood lamps in water- 
proof sockets can be used in these reflectors. 

Because of an increasing interest on the part of amateurs in this 
field we have designed a compact still camera (Fig. 10). It takes 
pictures 2 x /4 X 2 x /4 inches and is equipped with a rapid lens. All 
necessary controls can be operated under water and filters and polar- 
izing plate may be used. It incorporates a fitting for flash bulbs 
which is synchronized with the shutter. The only concession to the 
low price demanded of an amateur camera is a slight sacrifice in the 
convenience and rapidity of operation. In a short time we expect to 
have a similar case for one or more of the popular 16-mm. motion 
picture cameras. 



1 HULBURT, E. O.: "On the Penetration of Daylight into the Sea," J. Opt. 
Soc. Amer., XXII (July, 1932), No. 7, p. 408. 

2 DARBY, H. H., JOHNSON, E. R. F., AND BARNES, G. W.: "Studies on the 
Absorption and Scattering of Solar Radiation by the Sea," Carnegie Inst. of 
Washington, Publication No. 475 (Oct. 15, 1937), p. 191. 

3 RAMAN: "Molecular Diffraction of Light," Proc. Royal Soc., 101 (1922), 
p. 64. 


MR. KELLOGG: For getting a light background, do you ever inject into the 
water something that will produce a milky cloud behind the subject so that it will 
not obscure the picture? 

MR. JOHNSON : We have never attempted to do that. There is so much milki- 
ness in the water naturally that we have never thought about adding any. The 
background tends to come up and hit you in the face. You are seldom more than 
twenty feet away when this nuisance light or haze light obscures everything. 
Generally we try to get as much animal or plant life or coral growth or sand bank 
or other physical object in the background rather than to leave a lot of this fog. 

MR. CRABTREE: Have you used artificial light? 

MR. JOHNSON: Yes. The trouble with artificial light is that we have to have 
such a tremendous quantity of it to amount to anything. The red rays become 
dissipated in heat, and of course most artificial light has plenty of red rays in it. 

MR. CRABTREE: Possibly the high-intensity mercury- vapor lamp would be 
useful. It would at least be water-cooled. 

MR. JOHNSON: It would be a better lamp than some of the others. In tank 
work I am inclined to use a lot of artificial light, but from below rather than up 

The light from a sodium lamp would introduce far less haze than that from a 
mercury lamp, but for underwater photographic use a lamp of high efficiency 
over a wide range of the spectrum should be selected. We therefore do not 
recommend either mercury-vapor or sodium lamps as especially useful to the 
underwater cinematographer. 

MR. CRABTREE: I noticed a tripod in one of the pictures. The construction 
seemed to be quite different from that of the normal tripod. 

MR. JOHNSON: The tripod was a specially built brass tripod, made like a slide 
trombone, so you could move it in and out from the standing position. It is 
made very solid, because under water one is pushed around a lot so he can not use 
a surface tripod. 

I. J. KAAR** 

Summary. Now that television standards have been agreed upon in the United 
States, commercial receiving sets will undoubtedly be available very soon, and regularly 
scheduled television programs may be expected at the same time. How good will the 
television be and what are the problems yet to be solved before television reaches the 
technical maturity that radio has today? These are questions of considerable interest 
to engineers in related fields, and are the subject matter of the present paper. The 
quality of present-day television pictures is compared with that of motion pictures 
both in the theater and in the home. A discussion is given of the problems that have 
been solved to make television what it is today, and consideration is given to the 
problems that must be solved to make television what we hope it will be tomorrow. 
The problems of signal propagation and interference are discussed, and the matter 
of network program distribution is considered. Finally, a short introduction is 
given to the commercial problems in television. 

For several years the public has been increasingly curious to know 
when television would be introduced commercially, and a great 
variety of explanations have been advanced by uninformed persons 
as to why it has not happened already. Of course, at first the reason 
was lack of technical quality; but in the past few years the quality 
of pictures achieved has certainly been good enough to interest an 
increasingly large proportion of the population. However, two major 
questions had still to be answered before the widespread commercial 
introduction of television. The first of these was the fixing of satis- 
factory television standards and the second was the discovery of a 
satisfactory method of paying for the programs. The first matter 
has practically been settled; the second has not. 

Television differs from sound broadcasting very markedly in the 
importance of standards. In sound broadcasting, if the method of 
modulation (amplitude, frequency, or phase) is once determined, any 
receiver which can be tuned to the carrier frequency of a given trans- 
mitter can receive its program. The technical quality of transmitted 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 21, 

** General Electric Company, Bridgeport, Conn. 



programs can be improved year by year, but while this happens, a 
receiver once purchased is always usable, even though it may become 
outmoded as compared with current models. The situation in tele- 
vision is quite different. Due to the use of scanning and the necessity 
of synchronization between the receiver and transmitter, if trans- 
mission standards are changed, receivers designed for the old stand- 
ards become useless. Because of this fact, no responsible manufac- 
turer would sell receivers to the public until standards were fixed by 

FIG. 1. Typical scene in British television studio. 

the industry and sponsored by the Federal Communications Com- 
mission. Furthermore, American manufacturers did not desire to 
fix standards, except at such a high quality that widespread and 
sustained interest on the part of the public would be assured and so 
that adequate provision for continued perfection was possible. It 
required considerable technical perfection to justify these high stand- 
ards, but this has now been attained and the essential standards have 
been agreed upon. Consequently, it may be said with some assurance 
that the last technical obstacle in the path of commercial television 
has been removed, at least so far as the excellence of the picture under 
proper conditions is concerned. 



[J. S. M. P. E. 

The question of who shall pay for television programs has not yet 
been answered. As is well known, the cost of sound broadcasting is 
borne by "sponsors," who pay enough for their own programs to 
enable the stations and networks to fill-in the unsponsored time with 
sustaining programs of good quality and to make a profit in addition. 
However, this situation now requires the existence of tens of millions 
of receivers in the country with listeners who may be induced to buy 
the advertised products. Such an audience does not exist in television 

FIG. 2. Typical scene in American television studio. 

and can not be expected for several years. Of course, no such audience 
existed in the early days of sound broadcasting either, and the re- 
ceiver manufacturers themselves, along with a few individual com- 
panies who built stations for their own advertising purposes, operated 
the stations. In those days, however, the thought of something com- 
ing through the air, receivable at no cost, was an entirely new one. 
People were quite satisfied with the new toy as such and program 
excellence was a secondary consideration. This, of course, meant 
that the cost of broadcasting (as compared to the present) was low. 
Now the public has been educated to expect a high degree of excellence 

Jan., 1939] 



in program material and it is doubtful if mediocre program material 
in television would be acceptable. This has been quite strikingly 
proved in England. In other words, when television is born, it 
must be born full-fledged as far as program material is concerned. 
This, of course, means great expense which, undoubtedly, will have to 
be borne by the pioneers. 

In Great Britain commercial television is already a reality and it is 
of interest to consider some of its various aspects. American tele- 

FIG. 3. An outside pick-up in England. 

vision will be quite similar, except for improvements based upon the 
progress of the art since the British standards were set. 

Fig. 1 is a photograph of a television studio showing the general 
layout. In particular there is seen the performer and the position of 
the camera tube and the microphone. 

Fig. 2 is a similar set-up in an American studio. 

Fig. 3 is a scene showing a camera tube being used for outside pick-up 
in England. 

Fig. 4 is an unretouched photograph of an image on the screen of 
a picture tube in England. 

Fig. 5 is a similar picture taken in America. 



[J. S. M. P. E. 

FIG. 4. Photograph of picture tube image in England. 

FIG. 5. Photograph of picture tube image in America. 


Fig. 6 is a view of the antenna tower of the London (Alexandra 
Palace) Television Transmitter. The mast carries two separate 
aerials, vision (above) and the accompanying sound (below) . 

Fig. 7 is a view of the interior of a mobile television control room 
in England. At the center of the photograph are the picture monitors. 
This equipment is mounted in a "van" and has been used very suc- 
cessfully at sporting events. The signals in this case are transmitted 
to the main transmitter at very short wavelengths and rebroadcast 
at high power. 

Fig. 8 is a view inside an American "van" serving the same purpose. 


Let us next briefly consider the television standards which have 
been adopted in this country and the reasons for their adoption. The 
reader is no doubt acquainted with the general scheme of television 
used, but a quick review of the essentials may be in order. At both 
the camera tube and the picture tube, the picture is scanned by an 
electronic spot (beam of electrons) in a series of adjacent horizontal 
lines. The number of these lines into which the picture is divided 
in the scanning process determines the fineness of vertical detail 
which is reproducible. After scanning the whole picture, the elec- 
tronic spot then repeats the process at a sufficiently rapid rate so that 
no apparent flicker exists. This process is essentially the same, so 
far as the effect upon the eye is concerned, as that performed by the 
shutter on a motion picture projector. The frequency of repetition 
of scanning of the whole picture is known as the frame frequency. 

In order to conserve ether space, it is desirable to keep the frame 
frequency as low as possible. Consequently, an artifice is employed 
in order to increase the apparent frequency of repetition. This 
device is known as "interlace." In an "interlaced" picture every 
other line of a picture is scanned, and after the whole picture has been 
scanned in this way, the lines in between are scanned. This gives 
the physiological effect of scanning the picture twice, as far as flicker 
is concerned, even though all details of the picture have been com- 
pletely scanned only once. The apparent flicker frequency under 
these conditions which is twice the frame frequency, is known as the 
field frequency. Now obviously, if anything other than a complete 
blur is to be obtained, it is necessary that the number of lines per 
frame, the order of scanning of the lines, and the number of frame_s 



[J. S. M. P. E. 

per second be identical at the receiver and transmitter. These, ac- 
cordingly, have been standardized in America as follows : 

Number of lines per frame = N = 441 
Number of frames per second = F = 30 
Number of fields per second 60 (interlaced) 

To these we may also add the standard picture aspect ratio, which 
is 4:3 in agreement with the value used in motion pictures. 

FIG. 6. 

The Alexandra Palace television station in 

There is a reason for choosing the number 441 rather than some 
other number of about the same value. It may be shown that a 
necessary requirement for a stable relationship between the horizontal 
and vertical scanning oscillators, is that the number of lines per frame 
be a whole number having only small odd factors. If no factors 
larger than 7 be used, Table I shows the list of possible values of N. 
Four hundred and five lines per frame is the figure chosen as standard 
in Great Britain, while in some very fine laboratory pictures shown 
in Holland, 567 lines were used. 

Jan., 1939] 



<to O 

S & 




> i> X 

t- 10 X 



coX cocoX 




co coX co coXcocoX 


CO CO CO ^ T^ 10 


co 10 i> 10 X 

co co co co X 


26 I. J. KAAR [j. s. M. P. E. 

There is also a good reason for using 30 as the frame frequency. It 
is found that unless the frame frequency is a multiple or a sub- 
multiple of the power supply frequency, a shadow will move across 
the picture. This moving shadow has about the same physiological 
effect as flicker and is very disturbing. However, if the frame fre- 
quency is a multiple or sub-multiple of the power line frequency the 
pattern of the ripple is stationary on the image and it is much less 
objectionable. Therefore, since 60 cycles is standard in American 
power distribution systems, 30 frames per second has been chosen as 
standard for the frame frequency; since this is the smallest sub- 
multiple of 60 whose double is above the maximum flicker frequency 
observable by the eye. 

Among other matters requiring standardization are the synchroniz- 
ing operations at both the transmitter and receiver. It is clear that 
scanning at the transmitter and receiver must be exactly synchronous 
to within an extremely small error. In order to accomplish this, 
synchronizing signals are always transmitted with the picture signals. 
The purpose of these synchronizing signals is to start the scanning 
of both the lines and frames at exactly the right time. A detailed 
investigation of synchronizing signals would be out of place here, 
but it may be stated as absolutely essential that the type of synchron- 
izing signal transmitted should be completely standardized. 

The decision as to which was the most desirable synchronizing 
signal was one of the most difficult of all questions which confronted 
the Television Standardizing Committee. The signal shown in Fig. 
9 was ultimately fixed as standard. This synchronizing signal is 
described as of the "serrated vertical" type. It is believed that with 
the use of this signal, the most stable and accurate synchronization 
can be obtained. Furthermore, considerable latitude is offered to 
the designer as to the means chosen for utilizing the signal. 

The next subject which we wish to consider is the frequency chan- 
nel width required in television. It may be shown 1 that in order to 
transmit the available intelligence in a television picture with N 
scanning lines per frame, and a frame frequency of F, a minimum fre- 
quency range from zero to 

2 m 

is required. In this equation R is the aspect ratio. Substituting into 
equation 1 the values which have been standardized, we get 



28 I. J. KAAR [j. s. M. P. E. 

Thus for effective utilization of the intelligence available from a 
standard television picture, there must be complete and undistorted 
transmission of all frequencies from zero to at least 2,750,000 cycles. 
If this signal is used to modulate a radio frequency carrier, an ex- 
tremely wide frequency channel is obviously required. 

In order to economize on the use of the frequency band thus re- 
quired, single side-band transmission is proposed. The system may 
more properly be termed "sesqui-side-band." In this system, the 
elimination of one side-band is achieved by the use of band-pass 
niters which have a range of partial transmission in the region on 
either side of the transmission band. The carrier may be placed in 
one of these edge bands at a point where there is approximately 50 
per cent transmission. It may be shown that such a system has essen- 
tially double side-band transmission for very low frequencies, and 
single side-band transmission for medium and high frequencies. To 
return now to the question of utilization of the frequency channel, 
it is noted that by means of "sesqui-side-band" transmission the fre- 
quency band required by the picture signal is reduced by almost 50 
per cent. 

In transmitting television programs, it has been found desirable 
to transmit the picture and sound in the same channel. This allows 
a single oscillator to be used for both sight and sound in a superhetero- 
dyne television receiver, thus greatly simplifying tuning. In this 
system, the sound and sight signals are separated by selective circuits 
in the intermediate frequency amplifiers. Fig. 10 is a diagram of a 
typical television receiver, showing how it transmits and separates 
the picture and audio signals. 

In order to design television receivers, it is necessary that the rela- 
tive positions of the audio and picture signals be accurately known. 
In order that this should be possible, the following standards have 
been set : 

Television Channel Width. The standard television channel shall not be less 
than 6 megacycles in width. 

Television and Sound Carrier Spacing. It shall be standard to separate the 
sound and picture carriers by approximately 4.5 MC. This standard shall go 
into effect just as soon as "single side-band" operation at the transmitter is prac- 
ticable. (The previous standard of approximately 3.25 MC shall be superseded.) 

Jan., 1939] 







[J. S. M. P. E. 

Sound Carrier and Television Carrier Relation. It shall be standard in a tele- 
vision channel to place the sound carrier at a higher frequency than the television 

Position of Sound Carrier. It shall be standard to locate the sound carrier for a 
television channel 0.25 MC lower than the upper frequency limit of the channel. 

In addition to the standards already mentioned, there are certain 
other standards which have been adopted, and these will be com- 
mented upon briefly. Thus : 

It shall be standard in television transmission that black shall be represented 
by a definite carrier level independent of light and shade in the picture. 

This means that the background level is transmitted in a television 
signal, thereby eliminating the need for readjustment of the receiver 

FIG. 10. A typical television receiver. 

when the scene being televised changes from a preponderance of 
white to a preponderance of black. 

It shall be standard for a decrease in initial light intensity to cause an increase 
in the radiated power. 

A technical description of this standard is to say that the polarity of 
the transmission is negative. It is seen that a choice exists so it is 
necessary that this point be standardized, otherwise the picture tube 
at the receiver would frequently show the equivalent of a photographic 
negative. Even more important than this is the fact that unless the 
receiver were built for the polarity of transmission sent out by the 
transmitter, the synchronizing signals would not be effective. 

Jan., 1939] 



Percentage of Television Signal Devoted to Synchronization. If the peak ampli- 
tude of the radio frequency television signal is taken as 100 per cent, it shall be 
standard to use not less than 20 nor more than 25 per cent of the total amplitude 
for synchronizing pulses. 

Transmitter Modulation Capability. If the peak amplitude of the radio-fre- 
quency television signal is taken as 100 per cent, it shall be standard for the signal 
amplitude to drop to 25 per cent or less of peak amplitude for maximum white. 

Transmitter Output Rating. It shall be standard, in order to correspond as 
nearly as possible to equivalent rating of sound transmitters, that the power of 


Some American Picture Tube Characteristics 








If y * P * e 



















Green Screen 

White Screen 


15 7 /8 





Green Screen 

White Screen 


15 3 /4 







White Screen 









White Screen 


24V 2 





White Screen 

4" Projection 






Green or Yellow 

Green Screen 

* M-M magnetic deflection both ways. 

5-5 = electrostatic deflection both ways. 

** 5 = electrostatic focusing. 

S-M = combined electrostatic and magnetic focusing. 

television picture transmitters be nominally rated at the output terminals in 
peak power divided by four. 

Relative Radiated Power for Picture and for Sound. It shall be standard to 
have the radiated power for the picture approximately the same as for sound. 

The last four standards related particularly to output powers and 
power ratings, and while they are important in regulating the design 
of transmitters and receivers, they are not intimately connected with 
picture quality, which is of principal concern here. 

32 I. J. KAAR (j. s. M. p. E. 


When television is discussed by the public, the questions most fre- 
quently asked are "How good is television?" "How good will it 
be?" and "How much will it cost?" The answers to these questions 
involve such matters as : How large will the picture be ? How bright 
will it be? How much detail will it show? How clear will it be? A 
discussion of these considerations will be of interest. 

The standard high-quality television system which will possibly 
be commercialized shortly will have a 12-inch tube with a 7 ! /2 by 
10-inch picture. Three, 5-, 7-, and 9-inch tubes will probably also 
be standard commercial sizes. Compared with the size of a motion 
picture or even a home movie, these dimensions seem small. How- 
ever, considering the fact that the audience viewing a television 
picture will ordinarily not be more than perhaps four feet from the 
screen, and in the case of the small tubes, even one foot from the 
screen, these sizes do have considerable entertainment value. Any- 
one who has seen good pictures on 9-inch or 12-inch tubes will testify 
that when the program is interesting, the observer forgets that he is 
viewing television and becomes completely absorbed in the action 
on the screen. Nevertheless, it is reasonable to expect larger pictures 
in the best systems of the future. Table II shows the characteristics 
of some present-day television tubes. 

The matter of increasing the size of the cathode-ray picture pre- 
sents some serious obstacles. As tubes become larger they also be- 
come longer and their overall size becomes such that it is difficult to 
find suitable cabinets for them, which at the same time lend them- 
selves to attractive styling. For this reason, when a 12-inch tube 
is used, it is invariably mounted vertically in a cabinet, and the pic- 
ture is seen as a mirror image by the observer. Since a mirror causes 
a loss of light, and possible double images and distortion, it is an un- 
desirable adjunct at best. As a further difficulty, as cathode ray 
tubes are increased in size, they require more driving power, which 
is expensive, and higher anode voltages, which besides the additional 
cost, also represents a shock hazard. Thus the prospect of making 
cathode-ray tubes for home use with screen diameters exceeding 12 or 
possibly 15 inches does not seem promising at this tune. 

As an alternate method of increasing the size of the picture obtain- 
able by electronic means, the projection picture tube may be con- 
sidered. In this case a very brilliant picture on the screen of a 4-inch 
cathode-ray tube is enlarged by an external optical system and is 


projected on a screen to a size of, say, 3X4 feet. This system re- 
quires an exceedingly bright tube with a very fine spot. The ultimate 
size of projection tube pictures is limited, on the one hand, by the 
brightness obtainable from a fluorescent screen without causing its 
rapid deterioration and, on the other hand, by the detail which can 
be obtained which is closely associated with the fineness of the spot 
achievable. Projection tube apparatus is probably too large, compli- 
cated, and costly for home use, but for public performances of tele- 
vision programs, it undoubtedly has a future. 

Mechanical television systems have also been used for obtaining 
large pictures, with some degree of success. Of these, probably the 
most noteworthy is the system employed by Scophony. This system 
accomplishes modulation of the light-wave by utilizing fringe light, 
produced by virtue of passing a primary beam through a glass vessel 
in which is held gasoline or benzine, the liquid being subjected to 
vibration from a quartz crystal. The resulting modulated wave is 
then reflected successively by two rotating mirrors at right angles 
for accomplishing line and frame scanning. In the system as pro- 
posed, the line mirror rotates at a speed somewhat faster than 30,000 

Closely associated with the problem of picture size is the problem 
of picture detail. As has been pointed out, the vertical detail resolv- 
able in a picture depends upon the number of scanning lines, and the 
horizontal detail depends upon the ability of the electrical system to 
pass extremely high frequencies. In addition to this, of course, 
neither can go beyond the effective diameter of the electron spot. 
Observers have found that if the diameter of a picture element sub- 
tends less than one minute of arc at the eye, a picture contains essen- 
tially all the detail resolvable by the observer. If the observer is con- 
sidered to be 4 feet from the screen, a simple calculation will show 
that there are required 70 lines per inch and at 2 feet, 140 lines per 
inch. In present-day high-quality pictures on a 12-inch tube, with a 
7 1 /z inch X 10-inch picture, and 400 useful lines,* there are 53 lines 
to the inch. It is not unreasonable, therefore to expect the number 
of lines in television pictures to be a matter for attention in the years 
to come. 

Goldsmith states that a high-quality motion picture screen has 
5,000,000 picture elements. This would be equivalent to a 2000-line 

* Ten per cent of the 441 lines must be considered lost in the retrace interval. 

34 I. J. KAAR [j. s. M. P. E. 

picture, which would give 1 degree resolution on a picture 3 feet X 4 
feet in size, viewed from a point 5 feet away. While it is not too much 
to expect such television pictures sometime in the future, certainly 
a great many problems must be solved first. For example, such a 
picture would require 150,000,000 picture elements per second, which, 
at a conservative estimate, would need a band width of 80 megacycles 
per program for its transmission. This would undoubtedly require 
the use of quasi-optical carrier frequencies and the whole problem 
would entail development in many fields. To make this statement 
more striking, the band required would be 80 times as wide as the 
whole spectrum now allocated to all broadcasting in the United States. 

Another important consideration in television development is the 
problem of picture brightness. Cathode-ray tubes used in television 
receivers at present, are as bright as could be desired in a darkened 
room. Viewed in the daylight, however, or even in a well-lighted 
living room, their brightness is deficient. While it is always possible 
to darken motion picture theaters, television receivers will probably 
be expected to be more versatile, and to operate in bright light as 

The problem of increasing picture brightness is being attacked in 
many ways. Operating voltages, for instance, can be and are being 
increased. This, however, is undesirable from the standpoint of 
safety and cost. More efficient luminescent materials are, of course, 
the most obvious solution, and such materials are constantly under 

Another interesting development in this connection is the direct- 
viewing tube. This differs from the ordinary tube in that the bom- 
barded side of the screen is viewed, instead of the opposite side, as is 
customary. Such tubes naturally require a construction of unortho- 
dox shape. However, they may be the tubes of the future, both for 
reasons of brightness and also for reasons of contrast and detail, as 
will be pointed out later. Maloff 2 reports a direct-viewing tube having 
a maximum useful brightness of 100 candles per square-foot. This 
is more than ten times as bright as the highlights in a high-quality 
motion picture. 

Finally, there must be considered the matters of contrast and detail. 
The present contrast available in television tubes is quite good, but 
much still remains to be done. For one thing a cathode-ray tube 
exhibits the phenomenon of halation. This is the optical effect of 
the diffusion of light in the screen material, and with it we may also 


group the internal reflection of light from the walls of the tube. 
Halation is well known in photography. It decreases the brightness 
of highlights and diffusely lights up points which are supposed to be 
dark, particularly in locations near the highlights. The general effect 
is thus to decrease the available contrast and to limit the possible fine 
detail. The direct- viewing tube is a very effective means of decreas- 
ing halation. When such a tube is used, the increased contrast is 
very striking. 

In addition to halation, a cathode-ray tube also exhibits the 
phenomenon of "blooming," which is an electrical effect and results 
in defocusing the spot in the highlights. Improved focusing arrange- 
ments can be used to decrease "blooming," but even in the best of 
modern tubes it is still a problem. Since the contrast desired in a 
television picture requires an electronic beam of varying density, the 
focusing of the tube must be so arranged that the focal point does not 
change with current density, i.e., brilliance. This is not an easy prob- 
lem. However, it is evident that before the 2000-line pictures men- 
tioned above are ever obtained, great advances must be made in the 
cure of "blooming." 


The problem of signal propagation in television assumes an im- 
portance which, in many respects, is far more serious than that of the 
corresponding problem in sound transmission. In the first place, the 
exceedingly wide frequency channels required in television make it 
necessary that the signals be transmitted in the ultra-short-wave 
bands. At these frequencies, as is well known, there exists reliably 
only line-of -sight transmission, since there is no longer reflection from 
the Heaviside layer. While this fact limits the area of coverage of 
any transmitter, it is actually very desirable from the standpoint of 
interference. Thus there is far less likelihood of multiple images 
caused by multiple path reception, due to reflections from the Heavi- 
side layer, or of interference from a distant station operating at the 
same frequency, or from atmospheric "static." The only serious 
sources of noise at these frequencies are those generators within ap- 
proximately line-of -sight, of which noteworthy examples are automo- 
bile ignition systems and medical diathermy machines. 

While reflections from the Heaviside layer are negligible, neverthe- 
less, because of the very short waves employed, objects such as steel 
buildings, water towers, overhead wires, etc., provide efficient re- 
flectors and give rise to "ghost" images. The severity of this problem 

36 I. J. KAAR [j. s. M. P. E. 

will be realized much more fully than at present when the general 
public begins the erection of receiving antennae and the operation 
of receivers on a large scale. 

The line-of -sight limitation greatly increases the difficulty of serv- 
ing a large geographical area with a given program. A brief con- 
sideration of this problem will be of interest. It can logically be di- 
vided into two parts: 

(1) The conditions necessary for adequate coverage of the line-of -sight area, 


(2) The problems involved in network distribution. 

As a first step in finding the conditions necessary for adequate 
coverage of the line-of -sight area, we recall the formula 

S = V2r [Vh~i + VM = 3560 (VJh + Vfh] (3) 


5 = distance over which line-of -sight transmission takes place (in meters) 
h\ = height above intervening ground level of transmitting antenna (in meters) 
h 2 height above intervening ground level of receiving antenna (in meters) 
r = the radius of earth (in meters) 

This formula can readily be derived by geometrical consideration of 
the curvature of the earth. Next consider the formula 3 for the field- 
strength, near the horizon, from a transmitting antenna : 

E = voltspermeter (4) 



E = the field strength 

h = height of the transmitting antenna (in meters) 

a = height of above effective ground of the receiving antenna (in meters) 

T = distance of transmissions (in meters) 

X = wavelength (in meters) 

W = effective* radiated power from the transmitter (in watts) 

Now it is reasonable to expect a transmitting antenna to be located 
about 300 meters above ground and a residential receiving antenna 
to be a half-wave dipole located 4 meters above the roof (effective 
ground) while the roof itself is ten meters above ground. Under 
these circumstances there results from equation 3: 

S = 3560 (V300 + Vl4) = 75,000 meters 

= 75 km. or 46.6 miles (5) 

* If a transmitting antenna other than a half -wave dipole, such as a directional 
array, is used, the effective value of W may be increased in certain directions. 


This is the radius of the area over which reliable coverage can be ob- 
tained from the transmitter, provided that the power of the trans- 
mitter is sufficiently great. Consider, now what this transmitter 
power must be, in order to give reliable reception at the distance S 
from the transmitter. 

It is an empirical fact that reliable reception of a television pro- 
gram requires an input signal of about one millivolt. Now the effec- 
tive height 4 of the usual half -wave dipole receiving antenna is X/x. 
Therefore, the required transmitter antenna power is given by the 
equation : 

88\/W ah \ in _, 
-J35- ' - = 10 


W = 1 28 X lO-' JP_ . = 1.28 X10- 9 (75,000)* 
a 2 /* 2 4 2 X (300) 2 

= 27,100 watts* or 27.1 kw. (6} 

Actually, at the present time it is not feasible to radiate this much 
power, since no satisfactory tubes are available to generate it at these 
ultra high frequencies. 

Using two of the latest high-power developmental tubes in push- 
pull, it is possible to generate 10 kw. (40 kw. peak) at fifty megacycles. 
The limiting factor in this case is the fact that the size of high power 
tubes makes it impossible to tune them above a certain critical fre- 
quency and their high interelectrode capacities make it difficult to 
load them properly and still preserve the desired band-pass character- 
istics. Thus with tubes of the present types, it is not yet possible to 
reach the desired power level; and the condition will become more 
serious as more of the still higher frequency channels are used for 
television. However, it is reasonable to expect that the ingenuity of 
tube designers will overcome this difficulty in the next few years. 
In the meantime, the condition can still be corrected by increasing 
the height of the transmitting antenna, and especially of the receiving 

As a result of the above, an interesting fact is evident. If the height 
of the receiving antenna is neglected in calculating the line-of -sight 
distance, there results : 

5 = 3560 vT 
* Slightly in error because formula 4 is extrapolated beyond the horizon. 

38 I. J. KAAR [J. s. M. P. E. 

Substituting this value of 5 into equation 6 there results : 

It is evident that this value of W is independent of h. In other words, 
it requires 12.9 kilowatts of transmitted power to generate a signal 
of one millivolt in a half -wave dipole 4 meters above the ground at 
the horizon. This value is independent both of the carrier frequency 
and of the height of the transmitting antenna. The latter result is 

FIG. 11. 

The effect of multiple-path transmission or reflection upon the 
received image. 

very surprising. It indicates that as the antenna height is increased, 
the same power still suffices to reach the horizon the increased dis- 
tance being just compensated by the increased antenna height. 

Another problem of considerable importance in the adequate cover- 
age of the line-of -sight area is the elimination of multiple reception 
or echoes. This problem is of practically no importance in sound 
broadcasting. To get a clear idea of the problem, suppose that in 
addition to the direct ray travelling from the transmitting to the re- 
ceiving antenna there is also a ray which reaches the receiving an- 
tenna by way of reflection from a large building. This reflected ray 


will have travelled a greater distance than the direct ray before reach- 
ing the receiver. The picture which it carries will therefore be re- 
tarded in time, and it will consequently cause a similar but slightly 
displaced picture to appear next to the desired picture. This is a 
very annoying effect, and great effort must be made to avoid it. This 
effect is illustrated in Fig. II. 5 

The path difference necessary to cause a disturbing echo can be 
easily computed. The time of retardation of the reflected ray is 
clearly equal to the difference in path of travel divided by the velocity 
of light. Then, remembering that the electron beam scans ( 4 /s X 
30 X 441 X 441) picture elements per second, the displacement of 
the echo from the main picture (in picture elements) is 

D = 4/3 X 30 X 441 X 441 

3 X 10 8 
= 0.026 times the path difference in meters 

In other words, a path difference of 127 feet will cause an echo dis- 
placement of one picture element. This is enough to detract from 
the quality of the picture. 

The elimination or reduction of echoes is a complicated problem. 
In metropolitan areas, due to the presence of many reflectors in the 
form of tall buildings, the problem is serious indeed. The usual 
solution is to use a directional antenna which will discriminate against 
the undesired signal. Horizontal polarization of the radiated signal 
has been found to improve the signal-to-noise ratio at television car- 
rier frequencies, and its use will therefore probably become a standard 

Some of the problems connected with the chain distribution of 
television programs may now be considered. There are two general 
methods which have been used to transmit television programs from 
a key transmitter to a distant transmitter. These are the use of 
(1) the radio relay or (2) the coaxial (or other) high-fidelity cable 

Whichever method is used, the relay stations must be sufficiently 
close together so that non-fading noise-free signals are received at 
each repeater location. It has been found that relay stations must 
be located from 30 to 70 miles apart, the exact distance depending on 
noise conditions and (in the case of the radio relay) on the topography 
of the landscape. It has been customary to operate radio relays at 
wavelengths of two meters or less. Each relay station, of whichever 

40 I. J. KAAR [j. s. M. P. E. 

type, must reproduce the incoming signal with the highest fidelity, 
having neither amplitude, frequency, nor phase distortion. In other 
words, the picture must not be degraded in passing through the re- 

It is not surprising that the great problem in the relaying of tele- 
vision signals is cost. The cost per mile of a coaxial cable required to 
handle the exceedingly wide frequency bands of television programs 
is, at the present time, many times as great as the cost of correspond- 
ing networks used in sound broadcasting, both as regards initial cost 
and maintenance. If radio relaying is used, the cost of the relay trans- 
mitters required is obviously very great. However, the coming years 
are likely to bring great reductions in the costs of both methods of 
relaying, particularly the coaxial cable. 

This paper has been an effort to point out the fact that many 
problems still must be solved before fully satisfying television pic- 
tures will be available in the home. However, it is not to be con- 
strued that the commercial introduction of television will await a 
solution to these problems. Undoubtedly television will be com- 
mercialized in the near future and the problems will be solved as 
time passes much the same, for instance, as was the case in the mo- 
tion picture industry. One fact is very clear, that the further de- 
velopment of television must come largely through findings in the 
field, that is, by actual trial. 

The author wishes to acknowledge the assistance of Dr. Stanford 
Goldman in the preparation of this paper and the courtesy of the Na- 
tional Broadcasting Company and the British Broadcasting Com- 
pany for the use of photographs of their equipment. 


1 WHEELER, H. A., AND LOUGHREN, A. V. : Proc. I.R.E., 26 (May, 1938), No. 5, 
p. 558. 

2 MALOFF, I. G.: RCA Review, 2 (Jan., 1938), No. 1, p. 291. 

3 BEVERAGE, H. H.: Monograph "Television," RCA Review, 2 (1938), p. 99. 

4 HUND, A.: "Phenomena in High-Frequency Systems," p. 466. (McGraw- 

6 SEELEY, S. W. : "Effect of Receiving Antenna on Television Reception 
Fidelity," RCA Review, 2 (April, 1938), p. 435. 


MR. McNABB: Referring to the reproductions (Figs. 4 and 5) of a British pic- 
ture and an American picture, the line structure was quite evident in the British 
picture, but the contrast seemed a little better. Is the contrast better in the Brit- 
ish picture due to the method of transmission, or is the transmission of direct 


current along with the signal better than the American method of adding the d-c. 
at the receiving end? 

MR. KAAR: There is no essential difference in the method of transmission in 
England and here. The only difference is the means of synchronization. As far 
as contrast and detail are concerned, there should be no difference between the two 
systems except for the possible fact that we have 441 lines, whereas they have 405. 

It is possible to photograph any kind of picture from the front of a picture tube 
and we can so adjust focus and contrast as to make the line structure visible on 
an American picture. 

As a matter of fact, neither of these pictures is a good example because they 
have both been degraded by photographic processes in the original photograph, 
the enlargement, the negative, and the lenses, so in order to compare the two 
fairly the originals should actually be seen. Our pictures are somewhat better 
than the British pictures. 

MR. FINN: In the choice of repeaters, Mr. Kaar suggested that the choice as 
between coaxial cables and straight etherization of a program is very close. Is it 
your suggestion that the coaxial cable be used, over hill and dale for thirty or 
sixty miles, throughout the whole broadcast circuit, to blanket the country? 

MR. KAAR: That is a difficult question to answer because I am not familiar 
with the recent progress on coaxial cable. You will find a description of the New 
York-Philadelphia cable in the literature. As I remember, it has repeaters every 
ten miles and as yet will not transmit the full band required. Perhaps some day 
transcontinental cables may be laid capable of handling television programs, but 
I can not say that they will. The other system is satisfactory and has been tried. 
As to the economic balance between the future use of cables and ether channels, 
that still remains to be answered. 

MR. GOLDSMITH: The New York-to-Philadelphia cable was said to have cost 
$540,000. Whether that included large engineering developmental expenses or 
not, it is now known. In any case, that would have indicated a per-mile cost of 
$5000 or $6000. The major broadcasting networks in the United States today 
use somewhere on the order of 40,000 or 45,000 miles of lines, and if one multiplies 
that by $5000 for the cost of laying a similar coaxial cable network, the result 
of the multiplication is an extremely large and uneconomic amount. 

However, it is believed likely that development will lead ultimately to less 
costly coaxial cables with repeater stations closer together and satisfactory for the 
purpose, or to economic radio relay systems that will work very effectively. 

MR. KAAR: The fact that such a serious problem exists in chain programs comes 
pretty closely home to the motion picture engineer, because for the immediate 
present there is an answer to the chain broadcasting of television programs, 
namely, the transmission of motion picture films, which will undoubtedly be done 

MR. GOLDSMITH: There are many practical and artistic reasons why film will 
necessarily be widely used. 

MR. WILLIFORD: Does the adoption of the 60-cycle frequency as standard 
mean that communities having 25- or 50-cycle power supply are definitely out of 
the picture as far as television is concerned? 

MR. KAAR: There is no connection between the synchronizing mechanism of 
television and the power frequency. The synchronizing is accomplished by 

42 I. J. KAAR [j. s. M. P. E. 

transmitted signals. The only reason for and the advantage of choosing a frame 
frequency that is a multiple or submultiple of the power-line frequency is this: If 
a system should develop a ripple, as we know it in audio work, that ripple would 
occur at power-line frequency. If the frame frequency occurred at some other 
frequency than that, this ripple, which would be either a light area or a dark area, 
would travel across the screen. If the system is perfect and there is no ripple, 
it makes no difference at all. This is simply chosen as a safety measure. 

MR. GOLDSMITH: If the power-supply system of the receiver and its shielding 
are so engineered that no such effects appear, the receiver can be used equally well 
regardless of the power supply. 

MR. CABLE: It seems to me that the frequency chosen as 30 places a definite 
limitation on the picture brightness, because the frequency is a function of bright- 

MR. GOLDSMITH: The present standard is 60 pictures per second. We see 60 
"half pictures," with interlaced scanning. First is shown a picture with lines 
1, 3, 7, and so on, as a full picture; and the one with lines 2, 4, 6, 8, and so on, as 
the next picture, a sixtieth of a second later. So the frame frequency is 30 but the 
field frequency is 60 per second. You substitute for picture flicker a new effect 
called inter-line flicker, which is practically invisible. 

MR. FRIEDL: In selecting the number of frames projected, you have evidently 
regarded power-supply frequency as an important factor. Inasmuch as the mo- 
tion picture film will be used as a means of widely distributing the program, the 
frame-frequency of the motion picture is a consideration. I would judge, from 
the decision, that the more difficult matter of control is the power supply, but we 
as motion picture engineers naturally ask why the 24-frame frequency with in- 
terlacing to give 48 images was not considered the more important factor. 

You speak of standards in television. We are very standards-conscious in the 
SMPE and are aware of the importance of international as well as national stand- 
ardization. I see a lack of uniformity among the standards adopted by Germany, 
Great Britain, France, and America. That might be excused at the moment be- 
cause of the fact that the range of transmission is so limited and we can not expect 
immediately to transmit across the ocean; but inasmuch as the number of lines 
selected is 441, which has been selected mainly to allow room for improvement, can 
not we also anticipate improvement and have confidence in the effect of the de- 
velopment to look forward to transmission across the ocean, and, therefore, inter- 
national standardization? 

MR. GOLDSMITH: We may hope for this, because some such standard as 441 
lines for the picture might be adopted by all the nations. But it must be ad- 
mitted that at the present time radio differs from motion pictures in that interna- 
tional standardization is rather conspicuously absent. However, it may come 
with television. 

MR. FRIEDL: We are conscious of the high voltages in the larger tubes 25,000 
and 40,000 volts. What is the voltage on the 12-inch tube and how does the sys- 
tem meet with the protective requirements of the NFPA and the Fire Under- 

MR. KAAR : The voltage on the 12-inch tube will probably be 6000 volts. That 
sounds like a very serious matter, but really it is not. If you sit in a dentist's 
chair and he turns the X-ray on you, that is about 40,000 volts. It is protected. 


It simply means we have a job of protecting the television receiver, possibly by an 
interlocked back. 

MR. FRIEDL: All I can say is that conditions in the home where children might 
come in contact with the apparatus are different from what they are in a dentist's 

MR. GOLDSMITH: The back of the receiver is an expanded metal mesh. If you 
open the back, you will open all power circuits and discharge the high-voltage 
condensers automatically. If you try to take the cathode-ray tube out you will 
similarly open up the circuits. You can not get into contact with a high voltage. 
It is generally so arranged that even people with screw-drivers and determination 
simply can not get into trouble, and we hope these practices will continue. 

MR. FRIEDL: Does horizontal polarization mean that the antenna will be hori- 
zontal? Also, is that discussion of a three-meter receiving antenna going back to 
a multiplicity of "wash line" antennas on every roof? 

MR. GOLDSMITH: The antenna wire or rod is only about six feet long. The 
two component rods are each about three feeet long. 

MR. KAAR: They are half a wavelength long, and the wavelengths are of the 
order of five meters. 

MR. McNABB: In an article about six months ago in Electronics, regarding the 
quality of television pictures, it was the opinion of certain American engineers 
who investigated the British pictures that the British were ahead of us in their 
technical developments as well as their commercial exploitation of the art. 
That seems to disagree with the opinions of other American engineers. Exactly 
what are we to believe? 

MR. GOLDSMITH : The consensus of engineering opinion among those who have 
seen television pictures in London and New York is that there is little if anything 
to choose between them. It is most unlikely that practice in either case is far 
ahead of the other. 


Summary In a previous report of the Studio Lighting Committee the need of a 
catalogue of studio lighting equipment was emphasized. A number of papers have 
been published which describe various lamps and light-sources in detail, but there 
has not been assembled in one paper a symposium of all types of equipment and light- 
sources used on motion picture sets. 

This report covers all types of equipment in general use. The various lighting units 
are numbered and briefly described. Photographs of popular lamps are shown. 
Tables give minimum and maximum beam divergences, carbon and bulb sizes. 
Reference numbers are assigned to the various lamps for convenience in listing their 
characteristics. Data on light control devices and lamp filters are included. 


(1) MR Type 27 Scoop. Chromium plated reflector and Factrolite 
glass diffuser. Solenoid controlled. A twin-arc flood source, used for 
overhead illumination of walls, backings, and other areas that can 
not be lighted satisfactorily by spotlamps. Suspended singly or in 
groups. A smooth, general-purpose light-source. 

(2) MR Type 29 Broadside. Chromium plated reflector and 
Factrolite glass diffuser. Solenoid controlled. A twin-arc flood source 
that may be raised, lowered and tilted, and used as a floor-lighting 
unit for building up front light to the desired exposure level. 

(3) MR Type 40 Duarc Broadside. Chromium plated reflector 
and pebbled, sand-blasted Pyrex glass diffuser. An unproved motor- 
controlled twin-arc flood-lamp that takes the place of both scoop 
and broadside of the older types. 

(4) MR Type 65 Arc Spotlamp. Eight-inch diameter Fresnel- 
type lens. High-intensity rotating mechanism. Used for front and 
back lighting, close-up and medium shots. The intensity is almost 
uniform in the main portion of the beam, tapering off at the edges 
to permit overlapping adjacent beams without producing objection- 
able high-intensity zones. Within its energy capacity this lamp may 
be used for all photographic spot lighting. 

(5) MR Type 90 Arc Spotlamp. Fourteen-inch diameter Fresnel- 
type lens. High-intensity rotating mechanism. Used for back 

* Presented at the 1938 Fall Meeting at Detroit, Mich. 



FIG. 1. Typical high-intensity rotating element. 



FIG. 2. Typical solenoid feed mechanism. 



Lamp No. 

1. MR type 27 scoop. 

2. MR type 29 broadside. 

3. MR type 40 duarc broadside. 

Jan., 1939] 



lighting, sunlight effects through doorways or windows, etc., for key 
lighting on sets of moderate size, and for general front lighting into 
the rear areas of deep sets. 

(6) MR Type 170 Arc Spotlamp. Twenty-inch diameter Fresnel- 
type lens. High-intensity rotating mechanism. Used for back, cross, 
and key lighting, and for wide- and narrow-angle front and effect 

Lamp No. 

4. MR type 65 arc spotlamp. 

5. MR type 90 arc spotlamp. 

6. MR type 170 arc spotlamp. 
8. 36-inch sun arc. 

lighting. This unit has wider use for both black-and-white and 
color photography than any of the other arc units. 

(7) 24-Inch Sun Arc. Twenty-four inch diameter glass mirror. 
High-intensity rotating mechanism. Normally used with the arc 
crater facing the mirror and a clear glass door on the front of the 
lamp house. Where very sharp shadows are necessary the clear 
glass door may be moved to the position normally occupied by the 
mirror. A metal door is then placed on the open end. A large number 


of these lamps have been converted to use the same optical system as 
the MR type 1 70 lamp . Used for back lighting, sunlight effects through 
windows and doorways, etc., for key lighting on sets of moderate 
size, and for general front lighting into the rear areas of deep sets. 

(8) 36-Inch Sun Arc. Thirty-six inch diameter glass mirror. 
High-intensity rotating mechanism. Similar to the 24-inch Sun Arc 
except as to size. The 24-inch Sun Arc is rapidly being converted to 
the use of the Fresnel type of lens, but due to its great penetrating 
power, the 36-inch Sun Arc is valuable on extremely long throws and 
retains its popularity in its present form. When a large quantity of 

diffused light is required from this 
unit, a diverging door composed of 
strips of cylindrical lenses replaces the 
plain glass door. The lamp is used 
where a very high intensity of pro- 
jected light is required, as in back 
lighting behind a high level of fore- 
ground illumination; or where well 
denned shadows are required ; or where 
a clearly defined streak of light is 
required through the general illumina- 
tion; or for producing a general illu- 
mination of great penetration and high 

fl ~~J* ^ so ~ Am P ere Rotary Arc Spot- 

lamp. An 8-inch diameter plano-con- 
Lamp No. 10. 

vex condenser or 12 -inch Fresnel-type 

lens. High-intensity rotating mechanism. One of the early high- 
intensity arc spotlamps. This lamp is not suitable for color in its 
present form because of the spectral energy distribution of the carbon 
trim. A number of these lamps have recently been converted to 
the use of 11 mm. X 20-inch H. I. motion picture studio positive 
carbons to make them suitable for color photography. Used for 
back lighting on black-and-white sets and to increase the intensity 
of illumination at any point where projected light is required within 
the range of its intensity. 

(10) B & M Type 9 Twin-Arc Broadside. Chromium plated re- 
flector and glass diffuser. Solenoid striker with direct motor feed. 
A twin-arc flood source that may be raised, lowered and tilted, and 
used as a floor-lighting unit for use in building up front light. 



Arc Lamps for Set Lighting 

Ppsi- Nega- 

*Degrees Beam tive tive 

Lamp Divergencies Carbon Carbon 

No. Unit Min. Max. No. No. 

1 MR 27 Scoop 1 90 90 1 10 

2 MR 29 Broadside 1 90 90 1 10 

3 MR 40 Broadside 90 90 1 10 

4 MR 65 Spotlamp* 8 44 2 11 

5 MR 90 Spotlamp 3 8 44 5 14 

6 MR 170 Spotlamp 2 8 48 6 15 

7 24-Inch Sun Arc 2 **10 24 6 13 

8 36-Inch Sun Arc^ 10 32 6 13 

9 80- Amp. Rotary Spot* **8 30 4 12 
94 80- Amp. Rotary Spot 

(Converted) 8 44 3 12 
10 B & M Type 9 Twin- 
Arc Broadside 90 90 1 10 

* Approximate figures referring to usable photographic light. 
** With Fresnel-type lens divergences are approximately 8 to 44 degrees. 


Carbons for Set Lighting 

bon Arc 

No. Positive Carbons Amperes Volts 

1 8-Mm. X 12 NP MP Studio 2 '"' 7 '"'" 38-43 35-40 

2 9-Mm. X 20" Hilow Projector 6 ' 9 65-70 52-54 

3 11-Mm. X 20" HI MP Studio 9 90-95 62-65 

4 1/2* X 12" 80- Amp. Rotary Spot 2 ' 7 ' 8 ' 9 75-80 50-55 

5 13.6-Mm. X 22" HI Projector 4 ' 5 ' 9 110-115 54-56 

6 16-Mm. X 20" HI MP Studio 2 ' 4 ' 5 ' 7 ' 8 ' 9 140-150 64-67 

Negative Carbons 

10 8-Mm. X 12" NP MP Studio 

11 7-Mm. X 9" Cored Suprex Negative 

12 Vs" X 9" Cored 80-Amp. Rotary Spot Negative 

13 11-Mm. X 10" Plain-Cored MP Studio Negative 

14 3 /s" X 9" Cored Orotip Negative 

15 7 / 18 " X 9" Cored Orotip Negative 



Lamp No. 

20. MR type 36 studio spotlamp. 

21. MR type 26 studio spotlamp. 

22. MR type 16 cinelite. 

23. MR type 45 rifle lamp. 

24. MR type 220 18-inch sun spot. 

25. B & M type T5 studio spotlamp. 

Jan., 1939] 




(20) MR Type 36 Studio SpotlampA 6-inch diameter, 9-inch 
focus plano-convex condenser. For use where a full controlled beam 
of light is required: in close-up photography for back and close 
lighting, particularly where the photography demands high contrast 
of light and shadows ; in general motion picture set lighting it is use- 
ful for special effects and for illuminating areas that can be reached 
only by projected light. 

(21) MR Type 26 Studio Spotlamp. A spherical mirror is adjust- 
ably mounted behind the bulb to collect the rays of light and direct 
them upon an 8-inch plano-convex 

condenser. Used for back lighting, 
special effects, and particularly on 
sets where the general lighting must 
be in low key. 

(22) MR Type 16 Cinelite.A spun 
aluminum reflector, finished inside by 
wire brushing and chemical treat- 
ment, which gives it a diffusing 
characteristic. Used where light 
portable equipment is required. 

(23) MR Type 45 Rifle Lamp. 
Stamped metal reflector, chromium- 
plated with rifled corrugations for 
diffusion Used for general floor 

(24) MR Type 220 18-Inch Sun 

Spot. An 18-inch diameter parabolic glass mirror or faceted metal 
reflector, with spill ring as standard adjunct. Used for general 
illumination, for back lighting and cross lighting in small and 
moderate size sets, and for projecting light into back areas of 

(25) B&M Type T5 Studio Spotlamp. A short-focus Fresnel-type 
lens in front of the bulb and a small fixed spherical mirror behind the 
bulb project light forward into the field. This, in combination with 
the light projected around the lens from the 24-inch reflector, gives 
an even, intense light. For the large mirror, either a 24-inch diame- 
ter aplanatic reflector or a 10-inch focus glass mirror is used. The 
aplanatic reflector produces a very even field of light. Greater pene- 
trating power for long throws may be obtained with the parabolic 

Lamp No. 26. MR type 226 
24-inch studio sun spot. 



Lamp No. 

28. MR type 206 baby solarspot. 

29. B & M type 6 baby keg-lite. 

30. B & M type K keg-lite. 

Lamp No. 

31. MR type 208 solarspot. 

32. MR type 210 junior solarspot. 

33. MR type 214 senior solarspot. 


glass reflector. Used for back lighting, cross lighting, front lighting, 
and effect lighting. 

(26) MR Type 226 24-Inch Studio Sun Spot. A 24-inch diameter 
glass mirror, with a spill ring that allows only projected light to leave 
the lamp. Used for back lighting large sets, in which case the heads 
are removed from the pedestals and are mounted on parallels or plat- 
forms built at the top of the set or hung from the stage roof or ceiling. 


Incandescent Lamps for Set Lighting 

*Degrees Beam Bulb Bulb 

Lamo Divergencies No. No. 

No Unit Min. Max. **(B & W) (Color) 

20 MR 36 Studio Spotlamp 8 44 8 

21 MR 26 Studio Spotlamp 8 44 8 

22 MR 16 Cinelite 1 * 60 60 16 

23 MR 45 Rifle Lamp 60 60 4-5 15 

24 MR 220 18" Sun Spot 8 18 3-7 14 

25 B & M T-5 Studio Spotlamp" 8 40 2-3 13-14 

26 MR 226 24" Sun Spot 12 24 2 13 

27 B & M 24" Sun Spot 12 24 2 13 

28 MR 206 Baby Solarspot 11 8 40 9 

29 B & M Baby Keg-Lite Type 6 6 45 9 

30 B & M Keg-Lite Type K 4 44 3-7 14 

31 MR 208 Solarspot" 10 44 8 

32 MR 210 Junior Solarspot 11 10 44 3-7 14 

33 MR 214 Senior Solarspot 10 44 2 13 

34 Sky Light 180 180 2 13 

35 Broadside (Doubles) 90 90 5 15 

36 36" Sun Spot 12 24 1 12 

37 Overhead Strip Lamp 5 15 

* Approximate figures referring to usable photographic light. 
** For black-and-white photography. 

The lamps are used where a large quantity of light is to be supplied 
by a small number of units ; for front lighting on deep sets ; for cross 
lighting where high contrast is desired or on wide sets where the 
camera angle requires that the cross light be projected from a dis- 
tance ; for effect lighting such as in simulating sunshine through win- 
dows or doorways, or interior light into exterior darkness in night 
shots ; and for similar special requirements demanding beams of high 

(27) B&M 24-Inch Sun Spot. Similar to No. 26 in design and use. 


(28) MR Type 206 Baby Solarspot.A 6-inch diameter Fresnel- 
type lens. The small size of this lamp permits its use in places where 
the larger lamps can not be accommodated, particularly where it is 
necessary to conceal a source of high-intensity light. 

(29) B & M Baby Keg-Lite Type 6. A short-focus 6-inch diameter 
Fresnel-type lens combined with a pref ocused mirror ; used for special 
effects and where small units are required. 

(30) B & M Keg-Lite Type K A 10-inch diameter by 6-inch focus 
Fresnel-type lens. A set spherical mirror projects the rear light from 
the bulb toward the lens. A general purpose unit within its intensity 

limits; used for front lighting, back 
lighting, and modeling. 

(31) MR Type 208 Solar spot. An 
8-inch diameter Fresnel-type lens. 
A rhodium-plated spherical mirror is 
used at the rear of the bulb to direct 
the light toward the lens. Used for 
back lighting, modeling, and general 
front lighting within its intensity 

(32) MR Type 210 Junior Solar- 
spot. A 10-inch diameter Fresnel- 
type lens. A rhodium-plated spheri- 

Lamp No. 34. Sky light. J f 

cal mirror is used at the rear of the 

bulb to direct the light toward the lens. Used for back lighting, 
front lighting, cross lighting, and modeling within its intensity range. 

(33) MR Type 214 Senior Solar spot. A 14-inch diameter Fresnel- 
type lens. A rhodium-plated spherical mirror is used at the rear of 
the bulb to direct the light toward the lens. Used where high- wat- 
tage units are desirable, for back lighting, front lighting, and side 

(34) Sky Light. A shallow diffuse reflector about 24 inches in 
diameter. Used below and above sky backings and screens, where a 
flat even light distribution is required. 

(35) Broadside (Doubles). Two flood : type reflectors housed in one 
unit, used for floor, side, and overhead lighting: One of the first 
incandescent units made. 

(36) 36-Inch Sun Spot. A 36-inch diameter glass mirror. Used 
where the highest intensity of projected light is required from an 
incandescent tungsten source. 

Jan., 1939] 



(37) Overhead Strip Lamp. A trough-like unit containing sockets 
for five 1000-watt PS 52 bulbs. Used to supply fill-in light where 
it is difficult to use a more bulky housing. 


Incandescent Bulbs 


Bulb Rated 

No. Watts 


Bulb** Volts Amps. Base 

"MP" Type Lamps (for Black-and-White Photography) 



G-96 13 



G-64 13 



G-48 13 



PS-52 1 * 



PS-52 13 


****!, 000 

T-20 13 









T-20 13 









Mog. Bip. 
Mog. Bip. 
Mog. Bip. 
Mog. Scr. 
Mog. Scr. 
Mog. Scr. 
Mog. Bip. 
Med. Bip. 
Mog. Scr. 

"CP" Type Lamps (for Color Photography with Proper Filter) 

(All "CP" Type Lamps Operate ar 3380K. Color Temperature) 

12 10,000 G-96 11 110-115-120 87.0 Mog. Bip. 

13 5,000 G-64 n 110-115-120 43.5 Mog. Bip. 

14 2,000 G-48 11 110-115-120 17.4 Mog. Bip. 

15 2,000 PS-52 11 105-120 17.4 Mog. Scr, 

Additional Types Frequently Used in Studio Work 

16 1,000 PS-35 105-120 8.7 Mog. Scr. 

(No. 4 Photoflood) 

17 500 A-25 105-120 4.4 Med. Scr. 

(No. 2 Photoflood) 

18 250 A-21 13 105-120 2.2 Med. Scr. 

(No. 1 Photoflood) 

* Available also in Mogul screw base for older equipments. 
** G = spherical, PS = pear shaped, T = tubular, A = modified pear shaped. 
Numbers refer to diameter in 1 / 8 inch. 

*** Some units require the med. bip. base, others the med. scr. base or med. 
pref. base. 

**** Used in utility lamps, lighting fixtures, table and floor lamps. 




The terms applied to the various units of motion picture studio lighting equip- 
ment are legion and vary from studio to studio, and even from month to month. 
Sometimes a lamp is described by its type number alone; or by the rated current 

Lamp No. 

35. Broadside (doubles). 

36. 36-inch sun spot. 

37. Overhead strip lamp. 

in the case of arc -spotlights; or by the kilowatt rating of incandescent units. 
In some instances the mirror diameter supplies the name. Below are some com- 
monly used terms, the "Lamp Numbers" referring to the preceding sections: 

Side Arc 

1000- Watt Spot 














Twenty-Four Inkie 












Pan or Skypan 









The following are a few terms used for material and equipment associated with 
the use of studio lamps: 

Silks. Frames equipped with china silk diffusers, hung on the fronts of lamps 
to diffuse the light and reduce the intensity. 

Jellies. Frames equipped with chemically treated gelatin. Used for the same 
purposes as silks. 

Scrim. Black gauze used in various places to reduce intensity and diffuse 

Diverging Doors. Strips of cylindrical glass lenses. Used on Sun Arcs for 
light diffusion. 

Snouts. Various shapes of black sheet metal hangars. Used on the front of 
lamps to block out undesired light. 

Spill Rings. A series of sheet metal tubes, used in front of incandescent 
bulbs in mirror type lamps to block off angular rays emanating from the front 
surface of the bulb filament (see photographs of lamps 24-26). 

Spot Projector. A unit equipped with a condenser system that fits on the front 
of a Type 170 carbon arc lamp in place of the Fresnel-type lens; used to produce a 
sharply defined round spot of light. 

Gobos, Flags, Cheese Cutters, Niggers, Etc. It is often desirable to place opaque 
screens at various points on a set to keep all or a part of the light from reaching 
certain areas or objects. These screens are painted dull black and are rectangular, 
square, or circular, as the occasion may require. 


Carbon Arc Lamps. Carbon arc lamps 1-23 are used for Technicolor pho- 
tography without color filters. All types of high-intensity rotating arc lamps re- 
quire a Type Y-l straw gelatin filter. 4 

Incandescent Bulb Lamps. Where incandescent bulbs are used on Technicolor 
photography a special blue glass filter is required along with a series of CP Type 
bulbs, which burn at a uniform color temperature of 3380 K. n 


(All references are to J. Soc. Mot. Pict. Eng.) 

1 MOLE, P.: "New Developments in Carbon Arc Lighting," XXII (Jan., 1934), 
No. 1, p. 51. 

2 HANDLEY, C. W.: "Lighting for Technicolor Motion Pictures," XXV (Nov., 
1935), No. 5, p. 423. 

3 RICHARDSON, E. C. : "Recent Developments in High-Intensity Arc Spot- 
lamps for Motion Picture Production," XXVIII (Feb., 1937), No. 2, p. 207. 

4 HANDLEY, C. W.: "The Advanced Technicof Technicolor Lighting," XXIX 
(Aug., 1937), No. 2, p. 169. 

5 JOY, D. B , AND DOWNES, A. C.: "Characteristics of High-Intensity Arcs," 
XIV (March, 1930), No. 3, p. 291. 

6 JOY, D. B., BOWDITCH, F. T., AND DOWNES, A. C.: "A New White-Flame 
Carbon Arc for Photographic Light," XXII (Jan., 1934), No. 1, p. 58. 

7 BOWDITCH, F. T., AND DOWNES, A. C.: "The Photographic Effectiveness of 
Carbon Arc Studio Light-Sources," XXV (Nov., 1935), No. 5, p. 375. 


8 BOWDITCH, F. T., AND DOWNES, A. C. : "The Radiant Energy Delivered on 
Motion Picture Sets from Carbon Arc Studio Light-Sources," XXV (Nov., 1935), 
No. 5, p. 383. 

9 BOWDITCH, F. T., AND DOWNES, A. C.: "Spectral Distributions and Color- 
Temperatures of the Radiant Energy from Carbon Arcs Used in the Motion 
Picture Industry," XXX (April, 1938), No. 4, pp. 400-409. 

10 RICHARDSON, E. C.: "A Wide-Range Studio Spotlamp for Use with 2000- 
Watt Filament Globes," XXVI (Jan., 1936), No. 1, pp. 95-102. 

11 Report of the Studio Lighting Committee, XXX (March, 1938), No. 3, p. 294. 

12 Report of the Studio Lighting Committee, XXV (Nov., 1935), No. 5, p. 432. 

13 FARNHAM, R. E., AND WORSTELL, R. E. : "Color Quality of Light of Incan- 
descent Lamps," XXVII (Sept., 1936), No. 3, p. 260. 

C. W. HANDLEY, Chairman 





MR. GOLDSMITH: Is not this report the first assembly of such material in com- 
plete form? 

MR. GEIB : Yes. This is the first time anyone has attempted to give a com- 
plete catalogue of studio lighting equipment. 

MR. WOLF : Is the mercury- vapor arc lamp in commercial use? 

MR. GEIB : No. 

MR. WOLF: I understand they are used in Holland, in combination with 
sodium- vapor lamps to get a more balanced spectrum. 

MR. GOLDSMITH: It would be interesting to know whether that type of com- 
bination could be used for color photography because while it might give a sub- 
jective effect of white with the addition of sodium vapor-lamps, it certainly would 
not give the physically continuous spectrum of an arc or an incandescent lamp. 

It would therefore be interesting to know whether the Technicolor engineers 
could use a combination of that sort. 

MR. WOLF : I understand that the combination is used a great deal in Holland 
for television work and for studio work. 

MR. GOLDSMITH : As the pressure is increased in the mercury lamps the back- 
ground spectrum becomes more and more intense and a certain quasi-continuity 
of the spectrum is obtained. 

MR. CARLSON: That is correct. As the operating pressure in the mercury arc 
type of lamp is increased the continuity of the spectrum is definitely improved, 
together with an increased output of red energy. 

In the case of medium-pressure air-coole4 lamps the spectrum is still largely of 
the discontinuous or band type. The high-pressure water-cooled capillary lamp 
now on the market shows a continuous spectrum superimposed on the band 
spectrum. For still higher pressures the band characteristics largely disappear. 
Thus the mercury arcs that are now available are well adapted to monochromatic 
photography, but not for color work nor is their light easily filtered because of 
the "humps" in the energy vs. wavelength curve. Possibly the sensitivity charac- 
teristics of the color film could be adapted to the light. Information on the lamp 


was published in the September, 1938, issue of the JOURNAL by Farnham and Noel. 

MR. WOLF: What are the efficiencies of the light-sources now as compared 
with what they were, say, several years ago? 

MR. DOWNES : The efficiency of light-sources in the studios is, so far as I have 
been able to learn, not of great importance. What is wanted is a steady light- 
source, and one that can be directed to the particular part of the set with cer- 
tainty and assurance that it is going to continue to deliver uniform amount and 
quality of light during the time the photographing is done. 

The efficiencies in lumens per watt on the sets in the studios must vary through 
tremendously wide limits because of the fact that a very large number of the light- 
sources used are focused to deliver spots of various sizes on the set and as a result 
the luminous efficiencies are extremely variable. These various spot units can be 
focused to deliver spots from about three feet in diameter to very large ones, and 
it would therefore be very difficult indeed to obtain any figures for lumens per 
watt except with a bare light-source which, considering how they are used, would 
mean little or nothing. 




Summary. An account is given of the various types of photography used in the 
feature production "Topper." Among the shots discussed are a split screen against 
a projected background, demonstrating the feasibility of such treatment. Other ef- 
fects are: multiple exposures, animated split screen, animated travelling mattes, 
straight animation, intricate matching of action, and a new process of subtractive 

A statement is included on the precautions taken to eliminate weave between the 
production shots taken with Mitchell cameras and the duping, which was done on 
Bell & Howell machines. The paper is illustrated with various selections from the 
picture, made by the processes described. 

The reel witnessed at the Washington Convention of the Society 
on April 26, 1938, contained shots from the Hal Roach production 
Topper that are representative of the various types of trick photog- 
raphy used in the picture. They consist mainly of multiple expo- 
sures, animated split screen, animated travelling mattes, straight ani- 
mation, intricate matching of action, and subtractive matting. 

Most of the shots, particularly where the characters appear or dis- 
appear, are dupes made in contact on an optical printer with hard 
mattes in the optical head. The general procedure on the set was to 
take as much of the empty set as was needed, either before the scene 
was started or after it was finished, depending, of course, -upon which 
end of the scene the split screen was to be used. 

The camera was allowed to dolly or pan either before or after the 
part of the action requiring the split screen . At no time was the camera 
anchored. Of course, extreme care was taken not to move the 
camera while the portions of the scenes were being shot in which a 
character was to appear or disappear. 

In most instances the action was taken on the set exactly as if 

* Presented at the 1938 Spring Meeting at Washington, D. C. ; received 
Nov. 11, 1938. 

** Hal Roach Studios, Culver City, Calif. 



there were no split screen involved. The invisible actor either oc- 
cupied the position in which he would ultimately appear, or if the 
visible actor's action carried him too close to or past the spot, the in- 
visible one would run in and occupy his position as soon as the visible 
actor was sufficiently clear of his position. The invisible actor would 
then be cut out on a dupe and blank set substituted in his position 
until time for him to appear. 

The last three scenes in the reel shown at Washington of the two 
materializing in the car seat, Miss Bennett materializing on the bed, 
and the background shot driving down Broadway for various rea- 
sons were discarded, but were inserted in this reel to illustrate further 
what can be done by the simple treatment previously described. 

It will be seen from the preceding that there was nothing particu- 
larly new in Topper. It was made, we might say, by doing what had 
to be done by the best available system known to the operators in 
charge. It is almost safe to say that, with what is now known about 
what can be done in the handling of film, there is a way of solving any 
problem if the result justifies the effort. The text describing the 
various scenes accompanies the appropriate illustrations on the 
following pages. 



The first scene on the reel 
(Fig. 1), in which Constance 
Bennett and Gary Grant ma- 
terialize on a log, is a combina- 
tion split screen and lap dissolve. 
After Roland Young's action 
carried him to the left half of 
the set, the screen was split 
optically and a straight shot of 
the background substituted in 
the right half until such time as 
it took for Miss Bennett and 
Mr. Grant to enter and take 
their places. The matte was 
then dissolved out and the 
original scene dissolved in. 

FIG. 1. 

Jan., 1939] 



The scene showing Mr. Grant 
disappearing as he approaches 
the automobile (Fig. 2) is a lap 
dissolve from the scene showing 
him walking away into the set. 
The door of the car was then 
opened by an operator inside the 
car. The changing of the tire 
(the scene following that shown 
in Fig. 2) involved various types 
of animation, manipulating wires 
and concealed operators. For 
instance, the jack was manipu- 
lated by an operator in a pit 
under the car and the car let 
down by another operator. 

FIG. 2. 



The scene in which Constance 
Bennett "zips" herself out (Fig. 
3) was projected and mattes 
animated to follow the action of 
her hand. Miss Bennett got 
up and ran off the set as soon 
as her action was finished and 
Mr. Young held his position 
until she was clear. The length 
of film necessary to get her off 
the set was then cut out, and by 
use of the animated matte, plain 
background was made to re- 
place Miss Bennett as the 
"zipping" action progressed. 

The shot at the elevator 
where Miss Bennett and Mr. 
Grant disappear while holding 
up Mr. Young, was a simple 
lap dissolve. After they had 
decided that they should dis- 
appear, they held their position 
for a sufficient footage to cover 
the dissolve, then releasing 
Young, they ran off the set 
while Young continued with his 
action of swaying back and 
forth. The scene was then dis- 
solved as they faded away, 
shortening the amount of foot- 
age it took them to run out of 
the scene. Young's action 
matched up and he was dissolved 
back in again. 

FIG. 3. 

Jan., 1939] 



The shot of Miss Bennett with 
the vase of flowers (Fig. 4) was 
a split screen, lap dissolve, and 
wire shot. Young played the 
scene alone until after the box 
on the desk had been moved 
with wires, after which Miss 
Bennett entered the scene and, 
taking her position on the corner 
of the desk, lifted the vase. An 
operator watched the action 
through an anchored still cam- 
era, following the action of the 
vase and marking it on the 
ground-glass. The set was then 
cleared and from the same set-up 
the vase was lifted with wires as 
closely as possible in the path 
and at the same speed as Miss 
Bennett had lifted the vase. 
What discrepancy there was 
between the two actions of the 
vase was corrected optically on 
the lavender positive print and 
a split screen dupe made imme- 
diately in front of Young in 
which the clear set with the 
vase on wires was substituted 
until the vase started up at 
which time the set was dissolved 
out and Miss Bennett dissolved 

FIG. 4. 



The bit of feminine apparel 
walking by itself without visible 
means of support (Fig. 5) was 
photographed against black vel- 
vet on a girl wearing a black 
velvet suit. The shooting con- 
tinued up to the point where 
they were snatched off and 
put into the background by a 
rather involved process known 
as subtractive matting, in which 
the whole of a developed and 
fixed print is converted back to 
silver bromide and re-sensitized, 
after which the background 
printed into the heavy deposit 
of silver representing the black 
velvet. Snatching the pants off 
was a case of matched action. 
In one take that is, in the one in 
which the pants walked Roland 
Young snatched at them in an 
empty set. From the same 
position he snatched a real pair 
from a wire and the scenes 
were cut in action. 

FIG. 5. 


_^~- I ^ g 

Perhaps the most daring shot 
from a standpoint of braving 
possible technical troubles was 
the shot of Miss Bennett mate- 
rializing in the roadster (Fig. 6). 
This was a split screen shot 
against a projection background. 
Actually no difficulties were ex- 
perienced as precautions were 
taken to prevent them. The 
Mitchell camera taking the shot 
was, of course, equipped with 
precision pins. The lavender 
positives were printed tails first, 
on a Bell & Howell printer which 
uses the same perforations for 
registry as the Mitchell. A 
special shuttle was built for the 
optical printer registering pins 
at the bottom, so that through- 
out the whole process, the same 
perforations were used for regis- 

FIG. 6. 

The pen writing by itself 
(Fig. 7) in the close shot was 
straight animation. The pen 
was equipped with a pin in the 
point which was stuck into the 
blotter holding the pen upright 
as the animation progressed. 
The long shot was done with 

FIG. 7. 

FIG. 8. 

The shower-bath sequence 
(Fig. 8) was a composite of four 
shots. Efforts to photograph a 
person in a black suit under a 
shower proved surprisingly un- 
convincing. The effect finally 
was achieved by playing several 
jets of air against the water in 
front of a black velvet drop. 
The steam and the action of the 
soap were also taken against 
black velvet and the three shots 
doubled in over the shower-bath 
set. The fixtures were worked 
from the opposite side of the 
partition. Miss Bennett's ma- 
terialization after the shower 
was a simple split screen and 
lap dissolve. 

The following shot, however, 
in which she snuffs her cigarette 
out after she has dematerialized 
(Fig. 9) came dangerously near 
to being complicated. She was 
dematerialized in a split screen- 
lap dissolve, substituting the 
empty set in her half until she 
had time to run out of the 
original scene. The position of 
her cigarette which had been 
located on a still camera ground- 
glass, was matched and the 
cigarette carried down to the 
tray with wires. This bit of 
action then had to be substituted 
for the empty set. The last 
puff of smoke was then shot 
coming through a hole in black 
velvet and doubled in where 
Miss Bennett's face was last 

FIG. 9. 



The scene in which Grant 
materializes back of Eugene 
Pallette's arm (Fig. 10) de- 
pended more upon acting for its 
success than upon trick photog- 
raphy. Pallette struck his posi- 
tion in the alcove and held it 
without moving while Grant 
ran in and took his place behind 
Pallette's arm. After allowing 
sufficient footage for the transi- 
tion, they both picked up the 
action and continued the scene. 
In the dupe it was only neces- 
sary to shorten the scene with a 
lap dissolve the amount of foot- 
age it took Grant to get to his 

FIG. 10. 



[J. S. M. P. E. 

The scene in the cafe where 
both Miss Bennett and Grant 
disappear (Fig. 11) is what tech- 
nically is known as a "head- 
ache," the necessity of keeping 
the background action consistent 
being the principal problem. In 
this scene, which was a double 
split screen-lap dissolve, instead 
of dissolving the characters into 
an empty background, they had 
to be replaced by people, many 
of them moving. Perhaps it 
should be said that the shot was 
made by the "perseverance" 

FIG. 11. 

Jan., 1939] 



The stairway scene (Fig. 12) 
was made by the same method 
with slight variations. It may 
have been noticed that Young 
crossed to Grant's side of the 
screen the moment Grant dis- 
appeared. From the techni- 
cian's standpoint it was a mo- 
ment too soon, for Mr. Grant 
had not yet run off the set. 
As a consequence, it was neces- 
sary to animate the split screen 
matte which had been intro- 
duced to dissolve Grant out of 
the scene ahead of Young as he 
advanced, and re-animate the 
opposite matte which printed in 
the plain background without 
losing that almost imaginary 
line that makes a perfectly 
blended match. 

FIG. 12. 



Grant's sitting on the chande- 
lier (Fig. 13) was a split screen- 
lap dissolve. The only diffi- 
culty was that the closeness of 
the actors below necessitated a 
very sharp blend and an un- 
usually shaped matte. 

FIG. 13. 



Summary. In a previous paper the writer attempted to show that the latent photo- 
graphic image is formed in two distinct and separate steps. In the present paper this, 
theory is compared with recent physical research. The writer concludes that each of 
the photographic steps consists of the attraction of one electropositive silver ion to a 
sensitizing speck on the grain surface which has previously captured an electron. 

The reciprocity law failure at high intensities is explained by the minimum time re- 
quired for the attraction of a silver ion. The reciprocity law failure at low intensities 
is explained by assuming that a sensitizing speck which has attracted only one silver 
ion is unstable and that the number of grains activated by a single capture decreases 
exponentially with time. 

From these physical theories the writer deduces mathematical relations governing 
the photographic characteristics. H&D curves and reciprocity failure curves com- 
puted from these relations are in good qualitative agreement with experimental 

The assumption of an unstable intermediate state of insufficiently exposed grains 
implies certain effects of delayed fogging and delayed development which are verified 
by experiments. 

In a previous paper 1 by the writer, it was deduced from the shape 
of the photographic H&D curves that a grain of motion picture film 
must be hit by at least two photons in order to become developable. 
At that time, no physical explanation of this "double hit" theory was 
attempted and hope was expressed that the theory would be supplied 
by research physicists. 

There is, of course, no lack of research nor of physical theories in 
this field. On the contary, one is overwhelmed by an ever-increasing 
wealth of literature ; in fact, the writer's attention was called to some 
important contributions after completion of the analytical studies 
which form the basis of the present report. 

Unfortunately, the various investigators do not agree even in some 
of the most fundamental assumptions. While most of them assume 

* Presented at the 1938 Spring Meeting at Washington, D. C. 
** Electrical Research Products, Inc., New York, N. Y. 


74 W. J. ALBERSHEIM [j. s. M. P. E. 

that the latent image consists of silver atoms, recent work carried 
out in the Eastman-Kodak Research Laboratories 2 suggests that 
the solarized image alone forms a metallic silver cluster which is 
amenable to chemical-physical development only, whereas the latent 
image, being subject to chemical development, must be differently 
constituted. A further divergence of opinion exists with regard to 
the number of photons required for latent image formation. Some 
of the earlier research 3 showed that in single halide crystals the ratio 
of metal atoms reduced by light to the number of absorbed photons, 
i. e., the photochemical quantum -efficiency lies between one-quarter 
and one. Other workers stated 4 that a film grain in a photographic 
emulsion must absorb about 100 quanta in order to become develop- 
able, whereas a recent series of tests 5 proved that for various negative 
and positive emulsions the number of quanta incident upon an average 
sized photographic grain needed for formation of a latent image is 
of the order of 50. Since the grains are transparent and absorb only 
a fraction of the incident photons, their photographic quantum-effi- 
ciency must be considerably greater than l /w. 

We begin our survey of experimental knowledge with the photo- 
graphic toe characteristic. As shown in the previous paper, 1 the 
shape of the characteristic curve requires for the activation of the 
film grain by light, two separate physical steps which were mathe- 
matically represented in that paper by differential equations 49 and 
72. It must be understood, however, that these two steps are not 
necessarily to be identified with two single photons of light. They 
only mean two processes initiated by illumination in which the oc- 
currence of the second process depends upon the completion of the 
first, so that the probability (or average quantum-efficiency) for the 
formation of a latent image by a photon is the product of the separate 
probabilities for the two steps taken singly. The absolute number of 
photons required for the completion of each step affects the photo- 
graphic inertia rather than the toe shape of the characteristic which 
depends only on the ratio between the 2 efficiencies. This toe shape 
at low exposures is difficult to analyze from ordinary logarithmic 
H&D curves. It has been investigated by many authors but, in 
most cases, with sources of illumination quite different from visible 

Silberstein and Trivelli 6 as well as Jauncey and Richardson 7 found 
that the density of the developed photographic image originating 
from weak x-ray exposures grows in linear proportion to exposure. 


Silberstein and Trivelli also proved that the number of developable 
photographic grains is equal to the number of photons impinging 
upon the grain surface. For these x-rays therefore a "single step" 
theory is established. However, x-ray photons have an energy con- 
tent which is many thousand times greater than that of the visible 
light photons used in sound recording. Since a double step process 
is claimed for visible light, there must be an intermediate range of 
wavelengths at which a transition from the single to the double step 
occurs. This seems to be actually the case : 

FIG. 1. Characteristics of film exposed to x-rays and between 
double intensifying screens. 

Hirsh 8 showed that, although in images formed by hard x-rays the 
density increases proportionally to irradiation, the density-exposure 
characteristic begins to curve upward when the x-rays are softened 
to a wavelength of over six Angstrom units. 

This curvature means that the probability of latent image forma- 
tion is proportional to a power greater than one of irradiation so that 
on the average more than one photon per grain is needed for the latent 
image formation. 

In order to free the comparison between x-rays and light from the 
influence of the types of emulsion used, the writer asked the Eastman 
Kodak Laboratories to supply information regarding the different 
photographic characteristics of one and the same emulsion when 



[J. S. M. P. E. 

exposed to x-rays and to visible light. Mr. Wilsey of the Eastman 
Kodak Physics Department very kindly supplied the characteristics 
which are shown in Fig. 1 of this paper. Curve A of this figure is 
produced by x-ray exposure and shows a long sloping toe which in the 
previous paper 1 was shown to correspond to the "single hit" theory 
and incidentally to high transparencies of the emulsion. Curve B 
is obtained by exposing the same film between double intensifying 
screens. These intensifying screens are fluorescent surfaces which 
emit a great number of visible light photons when hit by a single 
x-ray photon. As stated by Mr. Wilsey "when the exposure is made 
with intensifying screens, practically the whole photographic effect is 
due to the fluorescent light from the screens so that the H&D response 



1.2 18 QA 


FIG. 2. Constant-density curves for different development times. 
A 5 minutes' development, B 30 minutes' development. 

is essentially that due to exposure to light on both sides of the film." 
It is evident that the toe of Curve B shows a much greater sharpness 
than that of Curve A corresponding to an exponent greater than one 
and therefore consistent with the double hit theory. (A three-step 
process can not play any important part in sound-film emulsions be- 
cause it would cause a toe-curvature greater than that found under 
actual conditions.) 

If one accepts the two separate steps of exposure as a fact, what are 
the known properties and time requirements assignable to these 
steps ? This information may be derived from a comprehensive series 
of tests conducted chiefly by Jones, Webb, and other physicists 
of the Eastman Kodak Laboratories on the subjects of "Reciprocity 
Law Failure" and "Intermittency Effect," which are closely linked 
to each other. The main features of the reciprocity failure effect 

Jan., 1939] 



may be illustrated by our Fig. 2 which is a reproduction of Fig. 9 
of a paper by Jones and Hall published in 1929. 9 In this figure 
the logarithm of exposures required to produce given densities is 
plotted against the logarithm of intensity. The reciprocity law 
assumed that the photographic effect depended only on the total 
number of photons impinging on the film grain ; that is, on the total 
exposure. If this were true the curves of Fig. 2 should be horizontal 
lines. Actually, the lines "fail" to be horizontal and curve upward 
at very low and very high intensities. Kron and Halm 10 re- 
ported that this curvature can be approximated by a catenary rela- 
tionship, which in Fig. 2 is illustrated by solid lines. However, at 
the left side of this figure one sees dashed lines breaking away from 

Ea&imao Slow Lantern P1a4es 

3.9 45 It 3.7 2.3 2.9 1.5 at 0.1 1.3 19 2.5 3.1 

FIG. 3. Constant-density curves for slow emulsion showing low- 
intensity departure from catenary equation. Top curve, density = 
4.2; bottom curve, density = 0.20. 

the catenary and rising at an angle of about 45 which limits the curve 
fitting range of the catenary and deprives it of physical significance. 
Another series of such curves is shown in Fig. 3 which is a reprint of 
Fig. 11 of the above-mentioned paper. In these figures, the logarithm 
of intensity is used as abscissa axis in accordance with historical 
precedent. This historical usage seems to the writer to be an un- 
fortunate choice which has for a long time beclouded the underlying 
physical relations. When one talks of a greater intensity in a physical 
process, such as a baseball hit, one thinks of greater speed or greater 
muscle tension. But when one talks of intensity of illumination with 
light of a given color, all the little baseballs, that is, the photons of 
light, hit their objective with the same speed and with the same 
energy of impact. What is meant by "intensity of illumination" 
is actually the number of photons per second, and denotes a quantity 

78 W. J. ALBERSHEIM [j. s. M. P. E. 

rather than a quality. The physical dimension of this "intensity" 
is energy times sec." 1 . Since the scale is logarithmic, it is only 
necessary to reverse the sides of the diagram in order to plot as 
abscissa axis the logarithm of the reciprocal factor; that is, of the 
average time interval between successive photon impacts upon a film 

This slight difference in the interpretation of the abscissa axis 
might have greatly speeded up the progress of research, for the im- 
pact time interval has recently been shown by J. H. Webb 5 to be a 
most important factor in the reciprocity law failure effect. In his 
investigation of the relation between reciprocity failure and the in- 
termittency effect, Webb discovered that intermittent exposures are 
equivalent to continued exposures with an equal total number of 
photons radiated and equal total duration, provided that the interrup- 
tion cycle is completed within the average time interval between 
successive photon impacts upon one and the same grain surface. 

Webb defines reciprocity law failure as the effect produced by the 
tune distribution of quanta reception by a photographic grain (in 
agreement with our double step theory) . 

This theory accounts for the reduced efficiency at both extremes of 
intensity, or rather of exposure time in the following way : Reciproc- 
ity failure at high intensities means that the first step requires for 
its completion a small but definite average time interval, before the 
second step can take place: If a new photon hit, or group of hits, 
occurs before the "step," i.e., the physical process initiated by the 
previous photon hit (or hits) has had time to be completed, the 
additional hits just "do not count" and very short exposures can not 
utilize all received light quanta for the production of developable 
photographic grains. 

Disregarding for simplicity's sake the statistical variations in the 
time requirements of the first step, we note for incorporation into our 
mathematical picture, that the effective time interval between successive 
photon impacts upon a film grain exceeds the actual time interval by a fixed 
minimum time which hereafter is called the "blocking time." 

In order to account for the reduced efficiency of the photographic 
process at very low intensities, that is, very long exposure times, it 
is necessary to make an additional assumption: The configuration 
produced by the first step of latent image formation must be elec- 
trically or chemically unstable , a stable latent image being only ob- 
tained by the completion of the second step. The simplest form of 


this assumption is that grains activated by completion of the first step 
fade back to the unexposed state according to an exponential time func- 
tion, as if the activated grains were a radioactive substance re-emitting 
the stored light energy in random manner. Some of this released energy 
may be detectable by photographic or other methods. The time after 
completion of exposure in which the number of activated grains is 
reduced by a factor e will be introduced into our equations as the 
"fading time." 

However, before attempting the mathematical analysis of this de- 
layed step-by-step mechanism, an attempt should be made to find a 
plausible physical explanation for the somewhat involved process of 
image formation which we deduced from two such well established 
every-day characteristics as the H&D curve and the reciprocity failure 

As previously mentioned, the research of Przibram, Smakula, 
Hilsch, and Pohl 3 shows that in single silver halide crystals the photo- 
chemical action consists of a liberation of silver atoms from their 
crystal bonds to the halide ions, the number of atoms thus reduced 
being proportional to the number of photons absorbed. This sug- 
gests that the two photographic steps are related to the number of 
deposited silver atoms rather than to the number of incident photons. 
This interpretation is made more probable by the above-mentioned 
fact that one and the same emulsion has entirely different character- 
istics when exposed to x-rays and to visible light. The powerful x-ray 
photons blast the required number of silver atoms out of the halide 
crystal in a single hit, whereas the weaker light photons can only dis- 
place them one at a time. The double step hypothesis is thus nar- 
rowed down to a "double atom" hypothesis. It implies two claims 
which must be substantiated : (a) That in spite of the low quantum 
efficiency of grain exposure, two silver atoms deposited at the right 
place are necessary and sufficient to make a photographic grain de- 
velopable; and (b) that the deposition of these two atoms proceeds 
in separate steps. 

Considerable light is shed upon the minimum size of development 
nuclei by the research of W. Reinders and his associates. 11 These 
investigators condensed extremely thin films of silver on glass plates 
and developed them in solutions containing a mixture of chemical 
developing agents and free silver salts. The minimum developable 
silver density turned out to be 1 /5ooth of that corresponding to a single 
atomic layer. The authors assumed that the deposited silver atoms 

80 W. J. ALBERSHEIM Q. s. M. P. E. 

combine into groups if they are condensed within a mutual distance, 
no larger than that vvhich separates them in a metallic silver crystal, 
and they computed the probability of various group sizes. The ob- 
served minimum density was found just sufficient to permit the oc- 
currence of four-atom groups. Hence it was concluded that aggre- 
gates of four or more silver atoms can serve as nuclei of development. 

It has been well established by the work of Sheppard and others 12 
that development starts at so-called sensitizing specks which seem 
to consist of silver sulfide molecules. Reinders found that sulfide 
molecules can act as centers of development just as well as silver 
atoms. Reinders and his associates then applied their probability 
calculus of group formation to the amount of silver sulfide present 
in photographic emulsions. They found that according to Shep- 
pard's reports there are several hundred silver sulfide molecules avail- 
able for each grain; that each grain is likely to have on its surface 
(and perhaps in its interior) several groups consisting of two sulfide 
molecules each; but that on only a small percentage of grains (less 
than 10 per cent) aggregates of three sulfide molecules will be formed. 
Now one may "put two and two together:" If two units of aggrega- 
tion are supplied by the sulfide molecules of the sensitizing specks and 
if aggregates of four are needed to make a grain developable, it is 
evident that two additional units must be supplied by the photo- 
graphic process in the form of silver atoms or silver ions. 

The manner in which the silver atoms find their way to the sensitiz- 
ing specks is explained by J. H. Webb 13 and by Gurney and Mott. 14 
According to quantum mechanics the primary action of the photon 
consists in knocking loose an electron from its attachment to a 
halide ion. If the electron receives sufficient kinetic energy it can 
travel freely through the previously insulating halide crystal as if 
the crystal were a metal. These electrons are "captured" at regions 
of the crystals in which the electrical potential is more positive than 
average. Such trapping points may consist of small fissures and ir- 
regularities in the crystal or, more likely, of impurities, such as the 
silver sulfide molecules of the sensitizing specks, which will be 
charged up to a higher negative potential by the captured electron. 

Gurney and Mott suggest that at normal temperatures the thermal 
agitation will throw some silver atoms out of their normal positions 
in the crystal lattice, producing slightly mobile negative "holes" and 
and highly mobile positive silver ions. The free silver ions are elec- 
trostatically attracted by the electrons captured at the sensitizing 


specks and move toward them like the ions in a liquid electrolyte. 
This description fits very nicely into our step-by-step pattern. The 
union, or at least close association, of a silver ion and an electron 
completes one photographic step by neutralizing the free charges. 
Since the net motion of the silver ion in the electrostatic field of an 
electron is relatively slow, it becomes plausible that the completion 
of this photographic step takes a measurable amount of time. Before 
neutralization of the charges the negative potential of the captured 
electron repels any further electrons which might be liberated by 
light and prevents them from reaching the same sensitizing speck. 
This, as discussed above, accounts for the reciprocity failure at high 

After completion of the first step the silver ion is not fully stabilized 
at the sensitizing speck. Due to thermal agitation there exists during 
each time interval a small probability that the electron which at- 
tracted it is thrown off or "evaporated." In that case the electron 
begins to travel freely through the crystal and is either captured by 
another sensitizing speck or by a crystal irregularity, or it may re- 
combine with the positive electron hole created when it was first 
knocked out of the crystal by the impact of the photon. This leaves 
a single silver ion unattached and it in turn resumes a random thermal 
motion through the crystal, probably being recaptured by a negative 
hole in the lattice. If, however, two steps are completed, that is, 
two silver ions and their electron mates are united at the sensitizing 
speck, they presumably form a silver molecule which is more stable 
than a single silver atom and much less likely to give up an electron 
by heat evaporation. By assigning silver atoms to the small nuclei 
of chemical development this mechanism 'differs from the view of 
Evans and Hanson 2 who attribute metallic nature only to the solarized 
nucleus. Possibly the discrepancy can be solved by assuming 
that in small nuclei containing very few silver atoms, these atoms 
remain closely embedded in the crystal structure so that chemical 
development can spread out from the sensitizing speck into the 
crystal. When the number of silver atoms grows due to over- 
exposure, they exert an increasing mechanical pressure upon the sur- 
rounding crystal. Finally this pressure will tear the silver cluster 
loose from the silver halide. The cluster can be physically developed 
by silver deposition but it is physically and chemically divorced from 
the halide crystal which reverts to the "unexposed" state minus a 
sensitizing speck. 



[J. S. M. P. E. 

The above physical interpretation follows closely the viewpoint of 
Gurney and Mott and differs from it mainly by assuming that the 
deposition of two silver atoms suffices to make a grain developable, 
whereas the said authors imply that a greater number is necessary. 
If two atoms only are required and if a single photon has sufficient 
energy to liberate an atom, why is it that on the average dozens and 
in some emulsions even hundreds of photon impacts strike a grain 
surface before it becomes developable ? The reason may be found in 
a relatively great number of sensitizing specks per film grain. Assume, 
for instance, that the grain contains ten sensitizing specks of which 

FIG. 4. 

Showing the reduction of photographic efficiency produced 
by an increase in the intensity of light. 

nine are located in the inaccessible interior of the grain and only one 
on the surface where it can be reached by the developer. Even if 
there were no other trapping possibilities but the sensitizing specks, 
the probability for a liberated silver ion to reach a sensitizing speck 
on the surface of the grain would be only Vioth. The probability of 
a second silver ion's reaching the accessible sensitizing speck pre- 
viously reached by the first ion would also be Vioth, so that the com- 
bined probability for the formation of a developable grain would be 
Viooth for two photon impacts, or 1 /2ooth per photon. 

The above-described mechanism accounts for the known experi- 
mental facts in a qualitative manner. As a next measure, therefore, 
it was brought into a simplified mathematical form. The differential 

Jan., 1939] 



equations governing the two steps and their solutions are given in 
the mathematical appendix attached to this paper. The equations 
differ from the double hit equations of the previous paper 1 by the 
blocking time required between the first and second step and by the 
gradual decay of film grains in which the first step only was com- 
pleted. At the limit of zero blocking time and infinite decay time 
which is approached for medium intensity, the new equations coincide 
with the old ones. The H&D curve at this medium intensity has 
been plotted as the extreme condition in the curves of Figs. 4 and 
5. Fig. 4 shows the reduction of photographic efficiency produced by 

FIG. 5. Computed H&D curves for long exposure times at decreas- 
ing intensities. 

an increase in the intensity of light. At extremely high intensity 
levels shown at the right side of Fig 4, the shape of the H&D curves 
approaches that of the x-ray characteristic, Curve A, in Fig 1. One 
reason for this is that the efficiency is at a minimum at the front sur- 
face of the emulsion where the excess of photons is greatest so that 
there is little difference between the photographic effect in front and 
rear of the emulsion : the effective penetration increases. Further- 
more, due to the abundant supply of freed electrons a second electron 
will reach every sensitizing speck and initiate the second step im- 
mediately after completion of the first step. This makes the photo- 
graphic process a function of the first step only, i. e., the equivalent of 
a single-step process. The time-scale gamma increases with intensity 



[J. S. M. P. E. 

due to the high penetrating power, and the straight-line portion of 
the H&D curve is shortened. 

In Fig. 5, a similar series of H&D curves has been computed for 
long exposure times at decreasing intensities. The photographic 
effect falls off first at the rear of the emulsion where a long time in- 
terval between successive photon impacts allows the end products of 
the first step to fade away before a second photon is received. Con- 
sequently, the effective penetrating power decreases, producing at 
extremely low intensities a reduced gamma and a straight-line portion 
of the H&D curve extending high up toward the shoulder. Whether 
this idealized relation is followed under practical conditions may be 


FIG. 6. Constant density curves, computed: "reciprocity failure." 

doubted. The great effective absorption requires extreme exposures 
in the front of the emulsion to obtain a reasonable overall density 
and this may lead to solarization and loss of density in the shoulder 

All characteristics of Figs. 5 and 6 are "time-scale" curves. The 
intensity-scale curves deviate increasingly from these for the more 
extreme exposure ranges: As shown in the Appendix, the ratio of 
time-scale gamma to intensity-scale gamma is a function of the slope 
of the reciprocity failure curve. 

By picking points of equal density on the various curves of Figs. 5 
and 6 and plotting their exposure logarithm as function of the in- 
tensity logarithm, one obtains "reciprocity failure curves" as shown 
in Fig. 6. Comparing these curves with the experimental curves of 
Figs. 2 and 3, one notes the similar character although the rise of 

Jan., 1939] 



the computed constant density curves at the high and low ends is 
somewhat too sudden. The shape of the measured reciprocity failure 
curves can be explained by considering that actual film emulsions 
do not have grains of uniform size and composition as assumed in 
our simplified calculations, but that they consist of a wide range of 
grain sizes containing different numbers of sensitizing specks. In a 
smaller grain it will, on the average, take less time for the silver ion 
to reach the electrified sensitizing speck, hence its blocking time is 
shorter. On the other hand, the statistical fluctuations are smaller 
in a smaller grain, thus reducing the probability for electrons to 
evaporate from the sensitizing speck and increasing the decay time. 


FIG. 7. Constant density curves, computed : "reciprocity failure. " 

Hence, actual reciprocity failure curves will be produced by the super- 
position of a great number of contributing curves which are trans- 
posed laterally. There will therefore be on each side of the curves an 
intermediate range of reduced and fairly constant slope, depending 
upon the statistical distribution of grain sizes. 

In Fig. 6, lines of equal exposure time have been drawn, in the 
form of thin straight lines rising at an angle of 45 degrees toward the 
right in a manner which seems to have first been used by Jones and 
Webb. 15 Since the reciprocity failure is determined by two time 
constants, namely, the blocking time and the decay time, it would 
be more instructive to plot the logarithm of the total irradiation (It) 
as a function of log T rather than of log /. This has been done on 



[J. S. M. P. E. 

Fig. 7. It is seen that the photographic process is completely ineffi- 
cient at exposure times shorter than the blocking time. At somewhat 
longer exposure times the required irradiation reaches a minimum, 
and at extremely long exposure times, exceeding the decay time, the 
required irradiation for constant densities increases with the square 
root of exposure time. 

Having thus verified that even in its simplified mathematical form 
the two-step theory fits the facts that led to its adoption, we con- 
sidered it necessary to put it to an experimental test by checking new 

A: AT" contrast without fogging. 

B: 2AE. 

C: AE-1000 cycle single amplitude. 

D: JEj-D.C. component of signal. 

G: E 2 -Foggmg. 

H: AT" contrast with fogging. 

/: Ei + 2 . 

FIG. 8. Increase of contrast by fogging. 

facts which can be predicted from it. The most significant of these 
facts seems to be connected with the claimed instability of the activa- 
tion produced by the first photographic step. In the under-exposed 
toe region of the characteristic the irradiation produces relatively 
very few grains in which the two steps of latent image formation are 
completed, but a much greater number, in which one step only has 
taken place, that is, one silver atom transported to a sensitizing speck 
on the grain surface. After development these under-exposed pic- 
tures show negligible contrast. However, their contrast can be in- 
creased by superimposing to the picture a constant illumination. 


This is known as "fogging," and depending on whether the super- 
imposed d-c. exposure takes place before or after the under-exposed 
modulated exposure, one speaks of "pre-fogging" and "post-fogging." 
The purpose and effect of fogging are illustrated by Fig. 8. According 
to our view, fogging can only be efficient if the time interval between 
the two superimposed exposures is smaller than the decay time so 
that the activated "single-step" grains do not have time to fade out. 
This theory was verified by the following "fading test": A sound- 
track was exposed to a thousand-cycle signal with very low intensity 
of illumination, E\ (Fig. 8) producing a specular density of only 
0.07. Upon this weak signal exposure we superimposed a uniform 
fogging exposure E z with about three times greater average light in- 
tensity. One part of this fogging exposure was applied ten minutes 
before the signal, a second part one-half hour after the signal, and 


Fading Test 

Hours between Relative Level Specular 

Signal and Fogging (Db.) Density 

No fogging -17.4 0.069 

-0.2 0.0 0.168 

+0.5 0.0 0.172 

+ 1.0 - 0.05 0.164 

2.0 - 0.2 0.165 

4.0 - 0.5 0.160 

6.0 - 0.75 0.158 

21.5 - 2.1 0.142 

further parts after increasing time intervals up to 21.5 hours. The 
result of this test is tabulated in Table I and shown on Fig. 9. It 
shows that fogging applied within 0.5 hour of the signal improves 
the a-c. output by 17 db. and that with increased time intervals this 
benefit was reduced by about 0.1 db. per hour. During the test time 
of 21 hours, the total average density decreased from 0.17 to 0.14. 
This decrease in density would have increased the level by 0.6 db. if 
the modulation had remained constant. The actual decrease of 
modulation therefore amounts to about 2.7 db. Since without fog- 
ging the signal level was negligible, the modulation loss can only be 
explained by a fading of the partly exposed grains in the time in- 
terval between signal and fog exposures. 

The change of average density, however, may have a double ex- 
planation : In addition to the fading effect proved by the signal loss, 


[J. S. M. P. E. 

there may exist an increase of the quantity of fully exposed grains 
available for development with time. Such an "intensification effect" 
has been mentioned in the literature. In the discussion of a paper on 
dry hypersensitization before this Society, 16 Mr. J. I. Crabtree of the 
Eastman Kodak Company stated, "It is well known that you may get 
effective hypersensitization or growth of the latent image by merely 
storing the latent image." The two-step theory leads one to expect 
such an intensification from the following reasoning: Assume that 
a film grain has ten sensitizing specks and that due to an insufficient 

-1.6 - 


#et*rtve tevei. 

8 ' artcui** Otfftrr~ 

Z 4 6 6 tO fZ 14 16 19 20 ZZ 

FIG. 9. Fading test; E. K. emulsion 1359. 

exposure five of these specks have received one silver atom each, but 
that in none of these specks the latent image has been completed by 
the absorption of a second silver atom. According to Gurney and 
Mott's theory, some of these specks will give up electrons by evapora- 
tion and these free electrons will move through the crystal just as 
if they had been liberated by an additional photon of light. There 
exists, therefore, a certain probability that one of these electrons will 
be captured by an "activated" sensitivity speck which has already 
received one silver atom. The capture of this additional electron 
and the subsequent attraction and absorption of a second silver ion 
will complete the second step for this grain and make it stable and 

Jan., 1939] 


developable. This process is, of course, much more likely to occur 
after weak exposures, when the number of partly exposed grains 
exceeds that of fully exposed grains. The intensification process will 
occur mainly in the toe region of the H&D curve. In a modulated 
sound-track exposed in the straight-line region of the H&D curve, 
the effect will be a considerable darkening of light portions and a 
small darkening of the darker portions, that is, a net loss of modula- 

This theory was put to the test in the following manner : Alternate 
sections of film were exposed with unmodulated light, 500-cycle 


4 5 6 7 

FIG. 10. Intensification test; E. K. emulsion 1359. 

modulation and with 8000-cycle modulation, and portions of all three 
types of exposures were developed after storing times increasing from 
1 to 13 days. The comparison of high-frequency and low-frequency 
signals was included because it had been suspected that some of 
the electrons liberated in the fading process might have sufficient 
energy to expose an adjacent grain and thus to produce an image 
diffusion recognizable as a high-frequency loss. The results of this 
test are given in Table II and Fig. 10. After correcting for the daily 
variations in development characteristics, there was an increase in the 
average density of the modulated as well as of the unmodulated sound- 
tracks amounting to about 0.01 per day and a loss of modulation 
amounting to about 0.35 db. per day. The small increase in the den- 

90 W. J. ALBERSHEIM [j. s. M. P. E 

sity of the unmodulated sound-tracks shows that the loss of modula- 
tion must be nearly entirely due to an intensification of the low-den- 
sity portions. These findings explain why the motion picture studio 
operators dislike recording films on the last day of the working week 
and storing them over the week-end before development. 


Intensification Test 

Days between Relative Modulation Average 

Exposure (Dh>.) Modu- Average 

and De- lation Specular 

velopment 500~ 8000~ Loss (Db.) Density 

1 0.0 - 0.7 0.0 0.62 

5 -1.4 - 8.3 1.35 0.69 

8 -2.4 - 9.4 2.4 0.71 

13 -5.1 -11.8 4.95 0.725 

Fortunately, the fading time of commercial emulsions at normal 
temperatures is so long that the photographic result is not noticeably 
impaired, provided development takes place within a day of exposure. 
For professional motion picture work, it does therefore not seem neces- 
sary to include the time loss of modulation due to low-density in- 
tensification into the analytical expressions for latent image formation 
which are cumbersome enough without this added complication! 
From the experimental point of view, however, the positive result of 
the fading and intensification tests has encouraged us to present the 
"step-by-step" or "two-atom" hypothesis as a small contribution 
to the comprehensive quantum theory of the photographic image 
formation built up by so many research workers and culminating at 
the present time in the work of Webb and of Gurney and Mott. 


1 ALBERSHEIM, W. J. : "Mathematical Relations between Grain, Background 
Noise, and Characteristic Curve of Sound-Film Emulsions," /. Soc. Mot. Pict. 
Eng. t XI (Oct., 1937), No. 4, p. 434. 

2 EVANS, R. M., AND HANSON, W. T.: Phot. J. (Aug., 1937), p. 497. 

3 PRZIBRAM, K.: Z. fur Physik, 20 (1923), p. 196. 
SMAKULA: Z.fur Physik, 59 (1929), p. 603. 

HILSCH, R., AND POHL, R. W. i Z.fur Physik, 64 (1930), p. 607. 

4 EGGERT, J., AND NODDACK, W.: (1932). See ref. 14, p. 156. 

6 WEBB, J. H.: /. Opt. Soc. Amer., 23 (May, 1933), No. 5, p. 157. 
6 SILBERSTEIN, L., AND TRiVELLi, A. P. H. : Communication No. 409, Eastman 
Kodak Research Lab.; Phil. Mag. (7th Ser.), 9 (1930), p. 787. 


7 JAUNCEY, G. E. M., AND RICHARDSON, H. W.: /. Opt. Soc. Amer. (May, 
1934), p. 125. 

8 HIRSH, F. R. : /. Opt. Soc. Amer. (Aug., 1935), p. 229. 

9 JONES, L. A., AND HALL, V. C.: Proceedings 7th Internal. Cong. Phot. (July, 

10 KRON, E.: Pub. Astrophys. Obs. Potsdam (1913), No. 67. 
HALM, J. R.: Astron. Soc. Monthly Notices (June, 1922), p. 473. 

11 REINDERS, W., AND HAMBURGER, L.: Z. fur Wissensch. Phot., 31 (1933), 
Nos. 1 and 2; Ibid., No. 10. 

REINDERS, W., AND DE VRIES, R. W. P.: Z. fur Wissensch. Phot., 56 (1937), 
Nos. 9 and 10, p. 985. 

12 SHEPPARD, S. E., TRIVELLI, A. P. H., AND LOVELAND, R. P.: J. Franklin 
Inst., 200 (1925), p. 51. 

13 WEBB, J. H.: J. Opt. Soc. Amer., 26 (Oct., 1936), No. 10, p. 367. 

14 GURNEY, R. W., AND Moxx, N. F. : Proc. Royal Soc., 164A (Jan., 1938), p. 

15 JONES, L. A., AND WEBB, J. H.: "Reciprocity Law Failure in Photo- 
graphic Exposure," /. Soc. Mot. Pict. Eng., XXIII (Sept., 1934), No. 3, p. 142. 

16 DERSCH, F., AND DURR, H.: "A New Method for the Dry Hypersensitiza- 
tion of Photographic Emulsions," /. Soc. Mot. Pict. Eng., XXVIII (Feb., 1937), 
No. 2, p. 186. 


(1) Physical assumptions and definitions 

(1.1) A latent image is formed by the deposition of two or more 
silver ions at a sensitizing speck located on the grain surface and ac- 
cessible to the developing agent. A grain in which this image forma- 
tion is completed is called "exposed." 

(1.2) Silver ions are transported to the sensitizing specks by the 
electrostatic attraction of electrons liberated by photons from the 
halide crystal and trapped by the sensitizing speck; this transporta- 
tion takes a measurable average time called the "blocking time," t b . 
The union of silver ion and electron neutralizes the free electron 
charge and completes a photographic "step." 

(1.5) Before completion of the photographic step the electron 
charge repels any further electrons and prevents them from being 
trapped by the same sensitizing speck. 

(1.4) A grain in which only one photographic step is completed, 
is in an unstable "activated" state. An electron and subsequently 
the silver ion attracted by it may be lost by thermal agitation. The 
time constant of this loss, i. e., the time in which the number of acti- 
vated grains is reduced by the factor e, is called the "fading time," 7}. 

92 W. J. ALBERSHEIM [j. s. M. P. E. 

(1.5) An "exposed" grain per 1.1, is stable and remains developable. 
(The fact that an excessive amount of deposited silver atoms may 
"solarize" the grain and make it inert to chemical development, is of 
no importance in the exposure range of motion picture sound-films.) 

(1.6) The grains are distributed at random throughout the photo- 
graphic emulsion. 

(1.7) Due to absorption the light intensity decreases nearly ex- 
ponentially with depth of penetration. The absorption constant n 
is defined as the reciprocal of the depth at which the number of 
photons per second is decreased by the factor e. 

(1 .8) Effective Electron Time Interval. The average time interval be- 
tween photon impacts on the grain may be called T P . The absorp- 
tion factor of single grains for photons is called p a . The probability 
that an electron is liberated by the absorbed photon, is called p e . 
The probability that a liberated electron penetrates to an unexposed, 
accessible sensitizing speck is called p ffl . The probability that a 
liberated electron penetrates to an activated accessible sensitizing 
speck, is called p g z. 

One finds the effective time interval between photo-electrons ar- 
riving at an unexposed speck : 


and the effective time interval between photo-electrons arriving at 
an activated speck 

CTi W 

(1.9) Additional Symbols (See list of symbols at the end of ap- 
pendix). In order to maintain a connection with the previous paper 1 
we define g as the fraction of the grains at a given depth in the emul- 
sion which has been activated but not fully exposed, and r as the fully 
exposed fraction. Where convenient, we use the fading factor: 

/ = i w 

and the intensity factor: 


(2) Differential equations for the steps of latent image formation 

(2.1) Equation for the First Step. The gross increase of activated 
grains is proportional to the available number of unexposed grains 
and to the intensity factor. From this gross increase one must deduct 
the decrease due to fading and the decrease due to a transformation 
of activated grains into fully exposed grains. Hence: 

dt Ti Tf dt 

or g' = (1 - r - f) i - fg - r' (6) 

(2.2) Equation for the Second Step. The increase of exposed grains 
is proportional to the available number of activated grains, divided 
by the effective electron time interval plus the blocking time : 

Hence g = r' (t z + t b ) (8) 

and g' = r" (t 2 + t b ) (9) 

(2.3) Solution for a Single Emulsion Layer. Introducing the values 
of 8 and 9 into 6 one finds : 

r + Ur' + Vr" = 1 (10) 

with U = Ti + (h + t b )(l + fTi) (11) 

and V = (tt + t b )Ti (12) 

A solution of 10 must have the form: 

r = 1 + ri-kit + r t -k*t (13) 

At / = 0, both r and g and, in view of (7), r' must equal zero. Hence 
13 can be transformed into: 

ri + r 2 + 1 = (14) 

riki + r 2 k 2 = (15) 

from this one finds : 

r, = r ^- r (16) 

k\ K 2 

r 2 - - ^ (17) 

and r = 1 + _A_ e -^ ***-** 

94 W. J. ALBERSHEIM [j. s. M. P. E. 

From 10 one finds for ki and k z the relation: 

r lf -kit (i _ Uki + W) + r 2 -*rf(l - Ufa + VW} = (19) 
from which it follows that : 

1 - Uki + VkS = 1 - Ukt + VW = (20} 

I (21} 

General Equation of H&D Curve. Equations 18 and 21 de- 
scribe the formation of the latent image at uniform intensity, and 
therefore at one given depth in the emulsion. The itensity itself de- 
creases exponentially with depth : 

i v = ioe~ uy (22} 

r< = I = T io ev (23} 

T z = C Ti = 5 = T 2o e" (24} 

If R is defined as the fraction of all grains in the emulsion which has 
become developable, one sees that after uniform development : 

R = D/D m (25} 

where D is the measured density and D^, the highest density obtain- 
able with the same emulsion and development. According to defini- 
tion, R is found as : 

^ r 

Y I 


r dy (26} 

in which dy denotes a differential emulsion layer and Y the total 
emulsion thickness. In view of 22: 

dy = -^ (27} 

*--4 ftr- _4_ f* w 

in which r is the transparency of the emulsion for the photographically 
active light. In order to make more clear which factors of 21 are 
functions of i, it may be transformed into : 


Combining IS, 25, and 28, one finds: 

D = - . ' 1-+ *L_ .-I- - *L- .-*- d 4 (30} 

- . f '( 

lnrJ iQT \ 

Equations 29 and 30 constitute the general solution for the H&D 
curve as function of the light intensity at the surface and the length 
of exposure, assuming, however, that all grains are uniform in size 
and constitution. 

(2.5) Evaluation of H&D Characteristics. If one introduces the 
full values of k from 29 into 30, the integral becomes very compli- 
cated and unmanageable for computation. It can, however, be sim- 
plified by the following considerations : 

The constant C in equations 2 and 29 denotes the decrease in prob- 
ability of electron capture by the presence at a sensitizing speck of 
one or more silver ions and electrons which neutralize each other's 
charges. The additional silver atoms may lower the work function 
and thus increase the probability of capture so that C would be some- 
what smaller than one. However, its magnitude will not differ much 
from unity and its effect will be about equivalent to a mere change of 
film speed. C will therefore be considered equal to one in the follow- 
ing computations. 

Furthermore, blocking time and fading time are of very different 
orders of magnitude : The blocking time is measured in microseconds, 
the fading time in hours. One can therefore regard the one as zero 
or the other as infinite, according to the intensity range explored. 
This splits the computation into a high-intensity and a low-intensity 

(2.51) Computation of High-Intensity Curves. Equation 29 is sim- 
plified into : 


Introducing the new variable : 

tbi = x one finds: (32) 

k y = 0.5* 

+ x I + x 

= i (34} 

L- (55) 

1 + x 

96 W. J. ALBERSHEIM [j. s. M. P. E. 

*yi + * _ i 

* - *yi + 



- 1 + x i * ( Q 7 \ 

i _ in + * - -5- ~ * 

Introducing the variable : 

t/tb = z one finds: (38) 

X \ X 

In view of 32 

-= and 

x ^ 


xz = it = e (43) 

(2.511) Approximate Solution at Relatively Low Intensities. At low 

lim x > (44) 

The integral of 42 can be rewritten : 

x* L *J 

For small x values this approaches : 

For a given exposure time : 

= = ^ hence (47) 

x i e 

= 1 + JL C e e-e (l+e)?Z and 

-fct J> --'?. 

Equation 45 is identical with equation 75 of the previous paper and 
confirms that at low intensities the blocking time does not have any 
influence upon the speed or the shape of the H&D curve. 

*e-*? (50) 


(2.512) Approximate Solution at Extremely High Intensities. At 
high intensities lim x > . This reduces 42 to : 

U-l + JL f 


D = D m (1 - e-*) = D m (l 

Equation 51 is a function of z alone, indicating that no matter how 
greatly one increases the intensity, a minimum time proportional to 
the blocking time is required for the formation of a latent image. 

The reciprocity failure curve is determined by the fact that t be- 
comes independent of i. Hence : 

MJ. = (52) 

a log i 

dlog e _ d log t + d log i _ 1 /^ 

d log i d log i 

Equation 53 defines the reciprocity failure curve as a straight line 
rising at an angle of 45 degrees. 

The shape of the H&D curve for extreme intensity, as expressed 
by 51, can be interpreted by comparing equation 51 with equation 
50 of the previous paper: 1 51 is identical with the function resulting 
from a single step process in a single "layer" of emulsion or in a com- 
pletely transparent emulsion. That is, the H&D curve at extreme 
intensities takes the shape of an x-ray characteristic. 

(2.51 3) Strict Solution of High-Intensity Equation . Equation 42 can 
not be completely solved in analytical form. By partial integration, 
however, it can be stripped down to residual terms of the form : 

This function was discussed and used in the previous paper. * (See 
equation 59, p. 431, and Fig. 5 of that paper.) 

Even with this abbreviating symbol, the solution for R or D re- 
mains rather complicated : 

D = ~ - '- l+ X rx 


e !+* Z (F e Fre) (1 z) 

*--"-+**, - vi + 

From this equation, the curves of Fig. 4 were computed. 

98 W. J. ALBERSHEIM [j. s. M. P. E. 

(2.514) Formulas for Gamma at High Intensity. The function for 
time-scale gamma is nearly as cumbersome as equation 55 because 
equation 42 does not become integrable by differentiating with regard 

y t = (RDoo) = D m = 0.434 D m - (56) 

d log t d log z dz 


VT < 57 > 

The intensity-scale gamma, however, can be freed of the integral sign : 

(2.52) Computation of Low-Intensity Curves. As discussed in the 
computation of high-intensity curves, the constant C of equations 2 
and 28 is assumed to approximate the value one. Furthermore, the 
blocking time is regarded as infinitely short compared to the long 
exposure times. Thus equation 28 is transformed into : 

k v = i + 0.5/ V(i + 0.5/) 2 - i* = i + 0.5/ Vfi + 0.25/ 2 (55) 
The following new variables are introduced : 

i/f = x (60) 

ft = z (61) 

2 = k/f (62) 
This transforms 18 into: 

r = 1 + 

with q = x + Vs == Vx + l / 4 (64) 

(2.521) Approximate Solution at Relatively High Intensities. lim 

63 can be written in the form : 

r = 1 + e~ (3i+22)z/2 I 2? c -(gi-<72)z/2 _ 

L 2i - 22 

^-l- e +( 3l -z 2 W2j (65) 


This approaches the value : 

, = 1 + -[ V5 2 - * - V* - ^t- 1 e + VJ,] ( 66 ) 

and, due to 

*Vx < 1, 

r = 1 - - (e + 1) 

^ = _ 1 
^ In r 

D = RD m =^= ~ [e-*r - -e - F e + F er ] (70) 

This equation is again identical with equation 79 of the previous 
paper, confirming that at high intensities the blocking time does not 
influence speed or shape of the H&D curves. 

(2.522) Approximate Solution at Extremely Low Intensities. Under 
these conditions, 

lim x -> (71) 

2l = 1 + * = 1 (72) 

22 = x* (73) 

r = 1 - e~* 2z =^ 1 ~' with (74) 

j = x*z (75) 

I? = -!_ C X r <^ = 1 f r 

\nrJ XT x ~ 2lnrjj^ j 


The density becomes a function of j alone. The reciprocity failure 
curve is determined by the equation : 

j = constant (78) 

d (long x 2 ) + d log z = (73) 

2d (log i) = d (log = (80) 

d (log e) = d (log *) + d (log = - d log t (&Z) 

The reciprocity failure curve becomes a straight line sloping downward 
at an angle of 45 degrees. 

The shape of the H&D characteristic 77 approaches that of a single 
step process, but with a low transparency, equal to the square of the 
actual transparency r. Accordingly, one sees in Fig. 5 that the toe of 

100 W. J. ALBERSHEIM [j. s. M. P. E. 

the extreme right curve becomes rounded, but that the straight-line 
portion extends way up toward the shoulder. 

(2.523) Strict Solution of Low-Intensity Equation. We have : 

R = - j_ r ** ( i + _IL_ -. L_ - 522 ) (82} 

In T Jrx x \ qi - q 2 ?i ~ 2 / 

__ i _, ! . ( } 

In T J rx x qi q z 

In the first integral of 83 substitute q\ = m* (84) 
One finds: 

x ^ m z m (85) 

dx = 2m - 1 (0) 

32 = (m - I) 2 (87) 

In the second integral of 83 substitute q. = 2 (88) 

One finds : 

x = n * + n (89) 

dx = 2n + 1 (90) 

<Z 2 = (n + I) 2 (W) 
This transforms 83 into : 

/0.5 +V0.25 + a: 
5+V0.25 + TX 

These simplified integrals can not be solved completely. But by 
partial integration they can be stripped to integrals of the above- 
mentioned type F( e ) and to probability integrals defined as : 

which can be found in tables. 
The solution becomes : 

Jan., 1939] LATENT IMAGE THEORY 101 

in which equation : 

ai = Vz (0.5 4- V0.25 + *) (95} 

a 2 = Vz(0.5 + V0.25 + r *) (96) 

b, = V7(-0.5 + V0.25 + *) (57) 

& 2 = Vz (-0.5 + \/0.25 + rx) (98) 

(2.524) Gamma at Low Intensity. The time-scale and intensity- 
scale gammas can be found by differentiation of equation 82 with 
respect to log / and log i, in a manner analogous to that shown under 
2.514. The calculations have been omitted from this appendix be- 
cause in motion picture sound recording the exposure range is gen- 
erally not in the low-intensity part of the reciprocity failure curve. 

(3) Equations of Reciprocity Failure Curve 

The concepts of blocking time and fading time were introduced 
into the theory in order to account for the reciprocity law failure. It 
will therefore be shown by the following derivation that, and how, 
the reciprocity failure curve is determined by the H&D curve 29. 

For a given emulsion and development, D m , r, t b , and T f are con- 
stants. k is a function of i v , and the integral 29, a function of i Q and 
/ only. (The suffix of i will be omitted below where no misunder- 
standing is possible.) 

Reciprocity curves are plotted with log e, that is, log (it) as ordinate 
and log i as abscissa. The density is held constant for any given 
curve. Since log i and log / are the only independent variables the 
constancy of D is expressed by : 

d log e = d log (it) = d log i + d log / (101) 

Equation 102 is the required relation between ordinate and abscissa 
of the reciprocity failure curve. 

102 W. J. ALBERSHEIM [j. s. M. p. E. 

(4) Reciprocity Curve and Intensity to Time-Scale Gamma Ratio 

In the "straight-line" region of the H&D curves, the partial differ- 
entials are denned as : 

dD/8 log i = 7 (intensity-scale gamma) (103} 

D D/D log t == yt (time-scale gamma) (104} 
Hence 102 may be rewritten in simplified form : 

The slope of the reciprocity failure curve equals one minus the ratio 
of intensity-scale gamma to time-scale gamma. At high intensities, 
such as used in sound-film recording, this slope is positive; hence 
the intensity-scale gamma is smaller than the time- scale gamma. 


Symbol Definition Dimension 

c = ** = t*Ti 

D = Density 

D = Saturation density 

e = it = relative exposure 

/ = 1/7/ = fading constant sec." 1 

F( x ) = I (\ e~ x } dx/x = integral function 


g = fraction of activated grains in an emulsion layer 
i = l/r = relative intensity sec." 1 

p = probability factor 

2 C x 

P x = I x*dx = probability function 


r = fraction of exposed grains in an emulsion layer 

R = fraction of exposed grains in the entire emulsion 

t = exposure time sec. 

tb = blocking time sec. 

/ 2 = electron time interval for second step sec. 

Tf = fading time sec. 

Ti = electron time interval for first step sec. 

u = absorption constant cm. -1 

y = extension into depth of emulsion cm. 

Y = total thickness of emulsion cm. 

a, b, k, j, m, n, q, U, V, x, z = auxiliary symbols, explained in 


e = basis of natural logarithms 

r = transparency of emulsion 

6 = partial differential 


MR. ALBURGER: What is the mechanism by which the electrons deposit the 
silver atoms on the crystal surface? 

MR. ALBERSHEIM: I am not a physicist; I can only guess that every atom in the 
molecular or crystal array has a certain electrical field surrounding it, and we 

Jan., 1939] LATENT IMAGE THEORY 103 

know that unless the electron has a certain speed it will be captured. A sharp 
corner produces a strong electric field; in ordinary wire we have corona effects 
that we would not have if the wire were round and polished. Something like 
that happens in the crystal, and at points of physical or chemical irregularity the 
electric field becomes strong enough to capture and retain the electron. When it 
is captured the excess electron will be attracted to the silver and rip it loose from 
the bond to the adjacent chlorine atom, and deposit it no longer as an ion but 
as a silver atom. The bromide shifts, and if it finds a resting place in the adjacent 
gelatin matrix it will probably come to rest there. * 

MR. GOLDSMITH: If a fully exposed negative is wound up on a reel over a nega- 
tive of a much less brightly illuminated subject, and the entire negative is pre- 
served some little time before development, is there found to be any trace of image 
transfer due to light re-emission from one end of the film to the other? 

MR. ALBERSHEIM : I have not found it in the literature, but by word of mouth it 
has been reported to me that such is the case, that under some conditions a pic- 
ture can be transferred from one emulsion to an adjacent one. It may be that 
this effect is not as dangerous as it seems, because the re-emitted electrons have 
a threshold value and it is possible that it might be easier to obtain the effect if 
the second emulsion has been sensitized to infrared. 

MR. DAVIS: I think the transfer of the picture from one film to another is the 
work of Sir William Abney, of England, some years ago, who made this experi- 
ment. He coated a plate and exposed it, and coated another emulsion on top ; then 
after developing, he stripped the coat and found a picture on the second coating. 
This probably was a development effect and not a bona fide latent image transfer. 

MR. FRAYNE: In view of the fact that the energy of the bullets you speak of is 
directly proportional to the frequency of the light, is the shape of the catenary 
curves dependent upon the frequency of the light that is used? 

MR. ALBERSHEIM: The influence of color is surprisingly small. I thought there 
would be such an effect, but this was disproved by the Kodak Research Labora- 
tories. Webb made an investigation of the influence of color from green, yellow, 
and reddish light, so far as the emulsion would take to ultraviolet of 3600 A, 
and the curves, while they came to different densities, were surprisingly close to 
parallelism. The curve seems just to shift in intensity, but not in character. 

MR. FRAYNE: Then in this case how do you explain the change of gamma with 

MR. ALBERSHEIM: That is probably due to a resonance effect. The emulsion 
is most sensitive to a certain wavelength, from 4000 to 4400 A. So long as the 
impinging light falls within that range nearly every grain will be exposed, and 
high ultimate densities and high gammas result. If we go down to 3500 A, 
many grains will not be exposed at all, so the emulsion acts as if it had fewer 
grains. We get lower gamma and lower ultimate density, and a coarser grained 
picture, relatively speaking. The grains are as big but there are fewer available. 

MR. GOLDSMITH: Would you assume that the re-emitted light is of the same 
wavelength as the original light producing the image? In other words, if a colored 
object is photographed, would a colored image be released? 

* Experiments conducted after the date of this discussion showed trace of this 


MR. ALBERSHEIM: I believe not. No matter how hard the light the electron 
will probably lose some energy, and when it is finally absorbed it is absorbed 
with just enough energy to liberate the silver atom. The excess is dissipated, then, 
perhaps as light or heat, so when the electron is re-emitted it will probably be re- 
emitted nearly monochromatically. 

MR. JONES: At the ultraviolet end, at least, the exposing radiation is absorbed 
by the thin layers, so you are working with a thinner and thinner emulsion, which 
of course gives a lower gamma. That is purely absorption. You do not have 
to invoke resonance to explain that. 

MR. ALBERSHEIM: If the emulsion were exposed to ultraviolet of sufficient 
density you would finally penetrate through, so that the ultimate density at very 
high exposures would still be the same. It would take very much more light to 
penetrate to the bottom, and I believe there must be some other effect involved 
because the ultimate gamma is lower. Also, if you expose with red light or green- 
ish light, which penetrates all the way through the emulsion, you still get the 
lower gamma. There may be a superposition of two effects there. 

MR. SANDVIK: If the change of gamma with wavelength is a resonance phe- 
nomenon, how would you explain the change in gamma when you use yellow dye 
in an emulsion and use blue light? 

MR. ALBERSHEIM: That would probably be due to the absorption effect that 
Dr. Jones has mentioned. However, the resonance effect is present because there 
is a fairly narrow absorption band in most emulsions. A single silver halide 
crystal exposed to light has a resonance frequency at about 4000 A where it ab- 
sorbs the maximum number of photons and is photographically most effective. 

MR. SANDVIK: It does that no matter what wavelength radiation is lost. 
The gamma is greatly decreased to the extent that the absorption takes place 
with the wavelength that is used. 

MR. ALBERSHEIM: I am glad to hear so. In that case we do not need ultra- 
violet for the sound-films to obtain reduced gamma. We can use the yellow dye, 
which we have been preferring all along. 



Summary. Test methods for the evaluation of motion-picture film for permanent 
records require test specimens too large to be removed from certain archival films. 
To assist those charged with the preservation of such films in determining the quality 
and checking the condition of them, suitable semimicro methods were developed for 
acidity, viscosity, and residual hypo content. Specimens as small as 7 mg. in weight, 
removed from the film with a small hand punch, gave satisfactory results for the 

(I) Introduction 

(II) Experimental testing 
(1) Acidity 

(2} Specific viscosity 
(3) Residual hypo 

(III) Summary and conclusions 


Certain repositories, such as The National Archives and some film 
libraries, are called upon to preserve films which can not be tested 
by the methods usually recommended for the evaluation of film for 
permanent records. From these films it is not possible to obtain 
test specimens of sufficient size for the usual tests without destroying 
some of the photographic images or making the film unserviceable 
otherwise. It is important that the condition of such films be de- 
termined. The nitrate films are chemically unstable, and successful 
preservation of records contained on them requires that they be ex- 
amined periodically so that disintegration can be anticipated and 
duplicates made of the records before they are impaired by visible 
deterioration. Good acetate film is stable, but it should be tested 
before placing it in storage to find if it was properly made and proc- 
essed. Also, subsequent testing of it may be desirable, particularly 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 3, 

** The National Archives, Washington, D. C. 
t National Bureau of Standards, Washington, D. C. 


106 J. E. GIBSON AND C. G. WEBER [j. s. M. P. E. 

if it should be exposed to unfavorable storage conditions. The 
semimicro methods described in this article were developed to permit 
the testing of such films without removing test specimens large enough 
to impair the film as regards legibility and serviceability. 


In studies 1 of the stability of photographic films, tests for copper 
number, viscosity, acidity, residual hypo (sodium thiosulfate), and 
flexibility were found to be of value. These tests were recommended 2 
for the evaluation of film for permanent records. Hence, the micro 
methods developed were modifications of some of these methods. 
The value of each of the proposed methods was determined by testing 
films that had been subjected to accelerated aging at 100C in oven- 
dry air for various periods of time. The data are thus comparable 
with those obtained by Hill and Weber 1 with test specimens of normal 
amount. The micro tests were made with test specimens weighing 
only 7 mg. each, which were removed from the films with a J /4-inch 
hand punch without causing appreciable damage to the film. The 
value of the micro test was judged by comparing the results of them 
with results obtained with the usual methods. The micro methods 
developed were for acidity, viscosity, and residual hypo. 

(1) Acidity. The acidity of the film was determined in the follow- 
ing manner. A single punching (wt. 0.007 g.) of film, including both 
base and emulsion, was transferred to a test tube and 5 ml. of acetone, 
containing 10 per cent of water by volume, was added. After com- 
plete dispersion of the film base, the acidity in H units was deter- 
mined by means of a commercial micro H-meter. The results are 
shown in Fig. 1 in comparison with ^>H values obtained with the same 
apparatus for seven punchings of film weighing 0.049 gram in 5 ml. of 
acetone containing 10 per cent of water by volume. 

The water and acetone were purified by distillation and the com- 
bined solvent had a pH of 7 ^ 0.4. Duplicate determinations on the 
film agreed within 0.1 pH unit. 

(2) Specific Viscosity. A punching of film (wt. 0.007 g.) was 
transferred to a test tube and dissolved in 5 ml. of acetone measured 
at 30 =*= 0.02C. After solution of the film base was complete and 
the mixture homogeneous, 3 ml. of the solution was transferred to an 
Ostwald viscosity pipette immersed in a constant-temperature bath 
(30 0.02C), and allowed to stand until temperature equilibrium 
was reached. The time of flow of the solution through the capillary 



of the pipette was measured with a stop-watch which could be read 
to one-fifth second. The time of flow of the pure solvent was also 
measured. Not less than three or four determinations were made for 
each solution, the values agreeing within two- or three-tenths of a 
second. The relative viscosity was then calculated as the ratio of 
the time of flow of the solution to the time of flow of the solvent. 

Fig. 2 shows the results of these measurements compared with re- 
sults obtained by Hill and Weber with one-gram samples. The 
different scales were necessary because different values are obtained 
by the two methods. 






10 20 


FIG. 1. Effects of accelerated aging on pH of cellulose 
acetate and cellulose nitrate films ; results obtained by the 
semimicro method compared with those obtained on larger 
test specimens. 

(3) Residual Hypo. The method used for detecting the presence of 
residual hypo (sodium thiosulfate) in films is a modification of the 
test proposed by Crab tree and Ross. 3 The method as modified con- 
sists in placing a single punching of film on a glass slide, adding two 
drops of mercuric chloride test solution to the specimen in such a 
manner that the solution flows over the specimen and onto the glass, 
and observing any turbidity that develops in the solution. The test 
solution contains 25 grams of mercuric chloride and 25 grams of 
potassium bromide in a liter of aqueous solution. The film is placed 
on the glass with the emulsion side up, and is allowed to stand for 2 
or 3 minutes after the addition of the test solution. It was found- 


J. E. GIBSON AND C. G. WEBER [j. s. M. P. E. 

that any turbidity of the solution can be best detected with the un- 
aided eye when the glass is held in the light so that the angle of in- 
cidence is approximately 90 degrees. 

If sodium thiosulfate is present, it reduces mercuric ion, and an in- 
soluble mercurous compound is formed which causes turbidity. If 
no thiosulfate is present, the solution on the glass remains clear, al- 
though the silver image is bleached white. Positive tests were ob- 
tained in this manner on single punchings taken from film that con- 
tained less than 0.05 mg. of hypo per square-inch. Positive tests 




FIG. 2. Effects of oven aging on viscosity of cellulose 
acetate and cellulose nitrate films as determined by the 
semimicro methods and by the usual methods. 

were also obtained with solutions containing 10 parts of hypo per 
million parts of water when a large drop of the solution was added to a 
drop of the test solution. 


Motion picture films that can not be sampled for testing by the 
usual methods can be tested by the semimicro methods. The ap- 
proximate quality and condition of the film can be determined by 
tests for acidity, viscosity, and residual hypo, using specimens weigh- 
ing only 7 mg. each, which can be taken from the film by means of a 
small hand punch without appreciable damage to the film. These 
methods are not recommended for use in selecting permanent record 
film. However, they are recommended to archivists and librarians 
for determining the condition of finished films given them for custody. 


With these tests, the approximate condition of the films can be found, 
and the necessity of making duplicate copies can be determined be- 
fore the damage to the films by deterioration is serious enough to be 
visible. The values obtained by the semimicro methods will differ 
somewhat from those obtained by the usual methods, but they ap- 
pear to show the extent of deterioration under accelerated aging 
equally well. When absolute values are used in judging the condi- 
tion of a film in question, those obtained by the semimicro methods 
should be compared with values obtained for new film by these 


1 /. Research, Nat. Bur. Standards, 17 (1936), p. 871; RP950. 

* Muse. Pub. Nat. Bur. Standards, M158 (1937). 

3 CRABTREE, J. I., AND Ross, J. F.: "A Method of Testing for the Presence of 
Sodium Thiosulfate in Motion Picture Films," J. Soc. Mot. Pict. Eng., XIV 
(April, 1930), No. 4, p. 419. 


MR. CRABTREE: Our recent researches have indicated that the milky compound 
formed by reaction of the mercuric chloride with hypo is not mercurous chloride 
but, rather, a double compound of mercuric sulfide and mercuric chloride having 
the formula 2HgS HgCl 2 . Such a compound has been described by H. Rose 
(Poggendorff, Annalen der Physik, 13: 59, 1828) and by Th. Poleck and C. Goercki 
(Berichte, 21: 2412-2417, 1888). 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

Journal of the Acoustical Society of America 

10 (Oct., 1938), No. 2 

Absorption of Sound in Carbon Dioxide and Other Gases 
(pp. 89-97) 

Measurement of Absorption in Rooms with Sound Ab- 
sorbing Ceilings (pp. 98-101) 

Absorption Effects in Sound Transmission Measure- 
ments (pp. 102-104) 

Absolute Sound Measurements in Liquids (pp. 105-111) 
Theory of the Chromatic Stroboscope (pp. 112-118) 

Adjustable Tuning Fork Frequency Standard (pp. 119- 

Recent Advances in the Use of Acoustic Instruments for 

Routine Production Testing (pp. 128-134) 
Frequency Ratios of the Tempered Scale (pp. 135-136) 
Harmonic Structure of Vowels in Singing in Relation to 

Pitch and Intensity (pp. 137-146) 
Apparatus for Direct-Recording the Pitch and Intensity 

of Sound (pp. 147-149) 

American Cinematographer 

19 (Oct., 1938), No. 10 

Flashes Across Nearly Sixty Years (pp. 403-404) 
Dunning Has Three-Color Process Now Ready to Go 

(pp. 406, 416) 
Mole-Richardson Introduces Duarc, New Automatic 

Broadside (pp. 407, 416) 
Ingenious Accessories Simplify Making of Special Effects 

Shots (pp. 408, 410) 

100 Watter Throws 150 and Whiter (p. 411) 
American Cameramen Lead. . . Pasternak (pp. 412-414) 















American Cinematographer 

19 (Nov., 1938), No. 11 

What's Wrong with Cinematography? (pp. 449, 457) 
Reeves Single System Sound Fits Any Camera (pp. 454- 


New Berndt-Maurer Sound Tract (pp. 456) 
20th-Fox Installs New Make-Up Lamps (p. 479) 

British Journal of Photography 

85 (Sept. 9, 1938), No. 4088 
Aluminum as a Photographic Base (pp. 568-570) 

Journal of the British Kinematograph Society 

1 (Oct., 1938), No. 3 

Modern Electric Discharge Lamps and Their Applica- 
tion to Kinematography (pp. 158-174) 
Volume Range Expanders (pp. 175-187) 
Manufacture of Motion Picture Film (pp. 188-204) 
An Optical System for Sound Reproduction (pp. 209- 

Bulletin de la Societe Francaise de Photographic et de 

25 Sere. 3 (Sept., 1938), No. 9 

Sur L'Obtention de Negatifs Photographiques a Grains 
Fins a Partir d'Emulsions ou d'Images a Gros Grains. 
(Obtaining Fine Grain Negatives Starting with Large 
Grain Emulsions or Images) (pp. 145-150) 

Educational Screen 

17 (Sept., 1938), No. 7 

Motion Pictures Not for Theaters, Pt. I (pp. 211- 

17 (Oct., 1938), No. 8 
Motion Pictures Not for Theaters. Pt. II (pp. 249- 

Preparing Sound Film Strips (pp. 254-256) 


11 (Oct., 1938), No. 10 

A Laboratory Television Receiver IV (pp. 16-19) 
A Shielded Loop for Noise Reduction in Broadcast Re- 
ception (pp. 20-22) 
Squeeze or Matted Track (p. 23) 
An Electric Timing Device (pp. 28-29) 

Ideal Kinema 

6 (Oct. 13, 1938), No. 71 

The Stableford All-Metal Screen, How It Is Constructed 
(P- 33) 


J. Mom 

J. H. McLsoD AND 








Kinematographic Weekly 

259 (Sept. 29, 1938), No. 1641 
Metals as Base for Picture Film (p. 36) 

260 (Oct. 27, 1938), No. 1645 
Metal Film Projection (p. 41) 

Television Principles in Kinematography (p. 41) 

International Photographer 

10 (Oct., 1938), No. 9 
Duplex Production Printer (pp. 6-7) 
Ultra-Fidelity Recorder (p. 7) 
Gevaert Revives 35-Mm. Raw Stock (p. 9) 
Technicolor Expands (p. 9) 
Projection-Revision of SMPE Standards (pp. 24-27) 


20 (Oct., 1938), No. 10 
Sicherheitsnlm im Normalformat (35 Mm. Safety Film) 

(pp. 255-256) 
Bildfilm und Magnetton (Magnetic Sound Recording on 

Film) (pp. 256-257) 

Methoden zur Messung des photographischen Gleich- 
richtereffektes (Method of Measuring the Photo- 
graphic Rectifying Effect) (pp. 258-264) 

Zwei neue Aufnahme-Materialen ; Agfa Superpanfilm 
und Agfa Ultrarapidfilm (Two New Films; Agfa 
Superpan and Agfa High-Speed Film) (pp. 264-267) 

Moderne Wiedergabegerate fur 16-Mm.-Tonfilm (Mod- 
era 16-Mm. Sound-Film Projectors) (pp. 268-269) 

International Projectionist 

13 (Oct., 1938), No. 10 
Advance Preparations Minimize Sound Emergencies 

(pp. 7-10) 

Television and Its Effect Upon the Motion Picture 
Theatre) (pp. 12-14) 

A Higher-Efficiency Condensing System for Tungsten- 
Filament Projectors (pp. 14-16) 

Projection Possibilities of Mercury Vapor Discharge 
Lamp (pp. 17-18) 

Photographische Korrespondenz 

74 (Oct., 1938), No. 10 

Fortschritte der Kinematographie im Jahre 1937 (Prog- 
ress of Photography in 1937) (pp. 164-167) 




W. Vox 









Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive V ice-President 

W. C. KUNZMANN, Convention Vice-President 

J. I. CRABTREE, Editorial Vice-President 

L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 

J. HABER, Chairman, Publicity Committee 

Pacific Coast Papers Committee 

L. A. AICHOLTZ, Chairman 




Reception and Local Arrangements 

H. G. TASKER, Chairman 







Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation 

G. A. CHAMBERS, Chairman 





114 SPRING, 1939, CONVENTION [j. s. M. p. E. 

Convention Projection 

H. GRIFFIN, Chairman 






Officers and Members of Los Angeles Projectionists Local No. 150 

Banquet and Dance 

N. LEVINSON, Chairman 






Ladies' Reception Committee 

MRS. N. LEVINSON, Hostess 

assisted by 







J. HABER, Chairman 



Equipment Exhibit 

J. G. FRAYNE, Chairman 




Headquarters of the Convention will be the Hollywood-Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Special hotel rates, guaranteed to SMPE delegates, European plan, will be as 
follows : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8 . 00 

Parlor suite and bath, 2 persons 12 . 00 

Jan., 1939] SPRING, 1939, CONVENTION 115 

Indoor and outdoor garage facilities adjacent to the Hotel will be available 
to those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately 
upon arriving at the Hotel. Convention badges and identification cards will 
be supplied which will be required for admittance to the various sessions, the 
studios, and several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges: 


Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 147.50 23.65 

Detroit 106.75 19.20 

New York 139.75 22.85 

Rochester 124.05 20.50 

Cleveland 110.00 19.20 

Philadelphia 135.50 22.35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips, sixty-day limits. Arrange- 
ments may be made with the railroads to take different routes going and coming, 
if so desired, but once the choice is made it must be adhered to, as changes in the 
itinerary may be effected only with considerable difficulty and formality. Dele- 
gates should consult their local passenger agents as to schedules, rates, and stop- 
over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems, and 
arrangements will be made to visit several of the studios. The Local Papers 
Committee under the chairmanship of Mr. L. A. Aicholtz is collaborating closely 
with the General Papers Committee in arranging the details of the program. 
Complete details of the program will be published in a later issue of the JOURNAL. 

Semi- Annual Banquet and Dance 

The Semi- Annual Banquet of the Society will be held at the Hotel on Thursday, 
April 20th. Addresses will be delivered by prominent members of the industry, 
followed by dancing and entertainment. Tables reserved for 8, 10, or 12 persons; 
tickets obtainable at the registration desk. 

Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the general office of the Society at the Hotel Pennsylvania, New York, N. Y. 


Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Inspection Tours and Diversions 

Arrangements are under way to visit one or more of the prominent Hollywood 
studios, and passes will be available to registered members to several Hollywood 
motion picture theaters. Arrangements may be made for golfing and for special 
trips to points of interest in and about Hollywood. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. N. Levinson, hostess, and the Ladies' Committee. A 
suite will be provided in the Hotel, where the ladies will register and meet for 
the various events upon their program. Further details will be published in a 
succeeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Li- 
brary and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at 
Ocean Park and Venice, Calif.; famous old Spanish missions; Los Angeles Mu- 
seum (housing the SMPE motion picture exhibit); Mexican village and street, 
Los Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the west, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, 
and Palm Springs, and special tours may be made throughout the Hollywood 
area, visiting the motion picture and radio studios. 

On February 18, 1939, the Golden Gate International Exposition will open 
at San Francisco, an overnight trip from Hollywood. The Exposition will last 
throughout the summer so that opportunity will be afforded the eastern members 
to take in this attraction on their convention trip. 



Results of the election of officers and managers of the Mid- West and Pacific 
Coast Sections of the Society are as follows: 


*S. A. LUKES, Chairman 

C. H. STONE, Past-Chairman *J. A. DUBRAY, Manager 

*G. W. BAKER, Sec.-Treas. **O. B. DEPUE, Manager 

(Pacific Coast) 
*L. RYDEE, Chairman 

J. O. AALBERG, Past-Chairman *C. W. HANDLEY, Manager 

*A. M. GUNDELFINGER, Sec.-Treas. **W. MILLER, Manager 

* Term expires December 31, 1939. 
** Term expires December 31, 1940. 

Elections of officers and managers of the Atlantic Coast Section are now in 
progress and will be announced in the next issue of the JOURNAL. 


At a meeting of the Section held on December 13th at the studios of RCA 
Photophone, Inc., New York, a paper was presented by F. C. Gilbert and E. S. 
Seeley of the Altec Service Corporation, New York, on the subject of "The 
Adjustable Equalizer as a Tool for Selecting the Best Response Characteristics." 
This equalizer is a device that can be inserted into theater reproducing systems 
for determining with a given horn system what characteristic is best in a given 
house. It is portable and can be carried into the auditorium, and has an ex- 
tremely wide range of variation. 

The paper was presented by Mr. Seeley and aroused considerable interest 
among the members attending the meeting, as evidenced by the protracted 
discussion held at the close of the presentation. A demonstration of the equalizer 
accompanied the presentation. 


At a meeting held at The Western Society of Engineers, Chicago, on December 
6th, Mr. J. Frankenberg presented a paper dealing with "Mechanical Sound 
Recording of Film." The meeting was well attended and the presentation was 
discussed at considerable length. 

Announcement of the officers and managers of the Section for the year 1939 
was made as listed above. 




On December 15th a meeting of the Section was held at the Walt Disney 
Studios in Hollywood, at which time a demonstration of the recording spectro- 
photometer and the Disney multiplane camera was given by the technical staff 
of the Walt Disney Studios. On account of limited accommodations, the meeting 
was open to only members of the Society and was well attended. The presenta- 
tion elicited much interest and discussion. 


Acknowledgment is due to many companies and persons for their cooperation 
in arranging and conducting the Detroit Convention, held on October 31st- 
November 2nd, with headquarters at the Hotel Statler. General facilities of 
the Convention were arranged by Mr. W. C. Kunzmann, Convention Vice-P resi- 
dent; Messrs. H. Griffin, J. Frank, Jr., and G. Friedl, Jr., in charge of projection 
facilities; Mr. K. Brenkert, Chairman of the Local Arrangements Committee; 
A. J. Bradford and J. F. Strickler on the Local Arrangements Committee; Mrs. 
J. F. Strickler, hostess in charge of the Ladies' Committee; Mr. J. Haber and F. 
Johntz of the Publicity Committee; and Mr. E. R. Geib, Chairman of the Member- 
ship Committee. 

Credit for the papers program and technical arrangements are due to Mr. 
J. I. Crabtree, Editorial Vice-P resident, and Mr. G. E. Matthews, Chairman of 
the Papers Committee. 

Among the companies contributing equipment and service to the Convention 
were the following: International Projector Corporation, National Carbon 
Company, National Theatre Supply Company, Raven Screen Company, East- 
man Kodak Company, Bausch & Lomb Optical Company, RCA Manufacturing 
Company, Brenkert Light Projection Corporation, Jam Handy Pictures Cor- 
poration, and the Detroit Local 199 IATSE. 

The Society is indebted to the following companies for the films loaned for 
the motion picture performance held on the evening of Monday, October 31st: 
RKO Radio Pictures, Paramount Pictures, Inc., Eastman Kodak Company, 
Technicolor Motion Picture Corporation, March of Time, and Walt Disney 
Productions, Ltd. 

Acknowledgment is due also to the United Detroit Theaters Corporation and 
the Fox Detroit Theater for supplying passes to members and guests during the 
week of the Convention. 


The following applicants have been admitted by vote of the Board of Governors 
to the Active grade: 


28 West 23rd St., 6601 Romaine St., 

New York, N. Y. Los Angeles, Calif. 


4431 West Lake St., 6601 Romaine St., 

Chicago, 111. Los Angeles, Calif. 


1620 Notre Dame St. West, 
Montreal, Canada 




Volume XXXII February, 1939 


Some Television Problems from the Motion Picture Standpoint 


Some Production Aspects of Binaural Recording for Sound 

Motion Pictures 


Coordinating Acoustics and Architecture in the Design of the 
Motion Picture Theater. . C. C. POT WIN AND B. SCHL ANGER 156 

Characteristics of Film Reproducer Systems 


Some Practical Accessories for Motion Picture Recording 

R. O. STROCK 188 

The Lighting of Motion Picture Theater Auditoriums 


Revised Standard Electrical Charactersitics for Two- Way Re- 
producing Systems in Theaters, Research Council, Academy 
of Motion Picture Arts & Sciences 213 

Organization of the Work of the Papers Committee 

G. E. Matthews 217 

Current Motion Picture Literature 225 

1939 Spring Convention, Hollywood, Calif 226 

Society Announcements 230 





Board of Editors 
J. I. CRABTREE, Chairman 




Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 


** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 
** Past-President: S. K. WOLF, RKO Building, New York, N. Y. 
** Executive Vice-P resident: N. Levinson, Burbank, Calif. 

* Engineering Vice-P resident: L. A. JONES, Kodak Park, Rochester, N. Y. 
** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 
** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 

* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. Y. 

** M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

* H. GRIFFIN, 90 Gold St., New York, N. Y. 

* D. E. HYNDMAN, 350 Madison Ave., New York, N. Y. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

* A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 

** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys, Calif. 

* Term expires December 31, 1939. 
** Term expires December 31, 1940. 



Summary. -Certain of the characteristics of television have their counterparts in 
motion pictures, and motion picture film and motion picture practice are applicable 
to television. Some of the problems and limitations pertaining thereto are outlined, 
and the following television-image characteristics are briefly discussed: (1) Number 
of scanning lines and the relationship to image size and viewing distance; (2) number 
of frames; (3) interlacing. 

The effect of film and optical system limitations on reproduced television images is 
illustrated by photographs, and curves are -given showing the spectral characteristics 
of Iconoscopes. The screen color characteristics of Kinescopes are also discussed, 
and the overall range and gamma characteristics of a television system are reviewed. 

The prime objective of television, in common with other pictorial 
arts, is to create an illusion. There are certain limitations on how 
good the illusion can be ; some inherent and others dependent on the 
state of the art. Many of these limitations have a counterpart in 
motion pictures and it is the purpose of this paper to review and com- 
pare some of these mutual restrictions. 


Picture detail in motion pictures is ultimately determined by the 
optical system and the resolution of the film. The factors determining 
picture detail in television are more complex. The frequency band 
width limitations imposed by a single-channel communication system 
suitable for television broadcasting makes it necessary to divide the 
scene arbitrarily into elemental areas and transmit the information 
representative of light and shade, area by area and line by line until 
the entire scene has been scanned. With such a television system the 
basic factors determining picture detail are the number of scanning 
lines, the size of the scanning spot, the frequency-band width, and 
the optical system. In practice the first two factors are definitely 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received December 
12, 1938. 

** RCA Manufacturing Co., Camden, N. J. 




[J. S. M. P. E. 

related, since the size of the scanning spot is commensurate with the 
distance between centers of scanning lines. In the television stand- 
ards of the Radio Manufacturers Association scanning is expressed in 
terms of the total number of lines from top to bottom from the begin- 
ning of one frame to the beginning of the next frame. Since in 
a practical television system both spot size and frequency-band 
width are chosen on the basis of the number of scanning lines, the 




FIG. 1. Pictures depicting characteristics representative of television 
images for several numbers of scanning lines. 

inherent resolution of a television system may be expressed as the 
number of scanning lines per frame. 

Information has been presented previously to indicate the degree 
of entertainment possible for television images of various numbers of 
scanning lines. 1 A summary of this will be presented here as the first 
step in our analysis of how good the television illusion will be. First, 
we may consider Fig. 1 which is made up of four repetitions of the 
same subject with detail equivalent to 60, 120, 180, and 240 scanning 
lines. From images of this type of motion picture film, from related 

Feb., 1939] 



tests, and from experience with television systems Fig. 2 has been 
made. This chart shows the relationship between number of scanning 
lines and picture size for several viewing distances. These curves 
indicate what the average eye demands for satisfactory images to 
produce the illusion expected of television. 

Another means for evaluating the resolution of a television system 
is to estimate its ability to tell a desired story in comparison with 
16-mm. home movie film and equipment. The result of such a com- 
parison by a number of observers is that a 400- to 500-line televi- 


















10 LJ 





























16 u 








































^ - 



^ - 

^- 1 


. -~ 







FIG. 2. Relationship between the number of scanning lines and 
picture size for several viewing distances. 

sion system compares favorably with 16-mm. home movies in per- 
mitting observers to understand and follow the action and story. 
The scanning standard adopted by the Radio Manufacturers Asso- 
ciation is 441 scanning lines per frame. 


Television images consist of rapidly superimposed individual frames 
much the same as motion pictures. In the case of motion pictures a 
group of time-related stills is projected at a uniform rate, rapid enough 
to form a continuous picture through persistence of vision. By 
present methods, each frame of a television image is built up element 

124 BEERS, ENGSTROM, AND MALOFF [j. s. M. p. E. 

by element in some definite order and these time-related frames are 
reproduced at a rapid rate. 

In motion pictures the frame frequency determines how well the 
system will reproduce objects in motion. This has been standardized 
at 24 frames per second. In television other factors than the ability 
to reproduce motion have made it necessary to use a frame frequency 
of 30 per second. 

Motion picture projectors commonly used are of the intermittent 
type. The usual cycle of such a projector is that at the end of each 
projection period the projection light is cut off by a shutter, the film 
is then moved a step so that the succeeding frame registers with the 
picture aperture, and the shutter then opens, starting the next projec- 
tion period. This is repeated 24 per second. Since projection at 24 
light-pulses per second with the screen brightness levels used in 
motion pictures causes too great a flicker effect, the light is cut off 
also at the middle of the projection period for each frame for a time 
equivalent to the period that it is cut off while the film is moved from 
one frame to the next. This results in projection at 24 frames per 
second with 48 equal and equally spaced light-pulses. Such an ar- 
rangement provides satisfactory results from the flicker standpoint. 

In television, because of the manner in which the image is recon- 
structed, a continuous scanning process, it is not practicable to break 
up each light pulse further by means of a shutter in a manner similar 
to that used in the projection of motion pictures. We therefore 
have in an elementary television system a flicker frequency corre- 
sponding with the actual frame frequency. This is satisfactory at 
very low levels of screen brightness but becomes increasingly objec- 
tionable as the screen brightness is raised. 

In motion pictures the projector shutter opening in terms of degrees 
for each frame has an important effect on the flicker characteristics. 
Cathode-ray tubes Kinescopes are at present the preferred means 
for television image reproduction. In the Kinescope each element 
of the image on the luminescent screen, when excited by the electron 
beam, fluoresces and assumes a value of brightness corresponding 
with the value of the electron-beam strength. Upon removing the 
excitation this brightness then decays (phosphoresces) in an expo- 
nential manner and at a rate dependent upon the screen material. 
The phosphorescence or persistence of the image screen aids the per- 
sistence of vision of the eye in viewing the reproduced image. This 
characteristic for one screen material is shown in Fig. 3. However, a 

Feb., 1939] 



previously stated, far too much flicker is present at 24 or 30 frames 
per second for the desired levels of screen brightness. 

A particular method of scanning is therefore used to modify the 
overall image flicker. This is possible because scanning is a con- 
tinuous process. Scanning may be in equal horizontal strips or lines 

from top to bottom in numerical order of lines 1, 2, 3, 4, 

(progressive scanning). This results in one overall light-pulse for 
each frame. If the procedure is modified so that scanning is for the 

first half of one frame period in the order of lines 1, 3, 5, 7, 9, , 

from top to bottom of the frame and for the second half of the frame 
period in the order of lines 2,4,6,8, 10, , from top to bottom 

Persistence Characteristic 
of Kinescope Screen 

.01 .02 .03 
Time In Seconds 

04 .06 


3. The phosphorescence characteristic of 
a Kinescope screen. 

of the frame (interlaced scanning), then the flicker effect of the repro- 
duced image is changed. This method of scanning is shown diagram- 
matically in Fig. 4. Each frame now consists of two portions (two 
fields) with respect to time: each field composed of a group of al- 
ternate lines, and the two sets of alternate lines are properly staggered 
to form a complete interlaced pattern. In progressive scanning each 
line flickers once per frame and neighboring lines differ in time rela- 
tion only by the time required for scanning one line. There is, there- 
fore, no noticeable inter-line effect. In interlaced scanning also each 
line also flickers once per frame, but neighboring lines differ in time 
relation by one-half a frame period. This results in two flicker effects, 
an overall effect and an inter-line effect. 



[J. S. M. P. E. 

As previously stated a frame frequency of 30 per second with pro- 
gressive scanning produces an intolerable flicker. A frame frequency 
of 60 per second is certainly satisfactory from the flicker standpoint 
but the frequency-band width required for transmission is doubled. 
With interlaced scanning at 30 frames, the overall flicker effect is 
the same as with 60 frames progressive scanning, and no increase in 
frequency-band width is required. Each line flickers at the rate of 
30 per second and adjacent lines flicker with respect to each other, 
since they are scanned with a time-difference of Veo of a second. At 
optimum viewing distances for television images and for practicable 
levels of screen brightness this inter-line flicker is not noticeable. 

A frame-frequency effect peculiar to television is encountered in the 
operation of cathode-ray television receivers from an alternating- 



FIG. 4. 

Diagrammatic illustration of progressive scan- 
ning and interlaced scanning. 

current power-supply system. The effects of ripple voltages and 
fields appear in the reproduced image in a variety of forms and from 
numerous sources. If the frame-frequency differs from the power- 
supply frequency, that is, differs except in terms of integral multiples 
or sub -multiples, then these effects move across the image at rates de- 
pendent upon the time-difference between the frame-frequency 
(multiple) and the power-supply frequency. This moving ripple pat- 
tern is almost as disturbing as flicker and the visual effects are about 
the same. Also for interlaced scanning these ripple effects cause mov- 
ing displacements in the position of alternate sets of lines and tend 
to destroy the interlaced pattern. If the frame-frequency has an in- 
tegral ratio to the power-supply frequency, 30 frames for a 60-cycle 
source, then the effects are stationary on the image and very much 
less pronounced, thus making it possible to obtain satisfactory per- 
formance when using comparatively inexpensive apparatus. 

On the basis of these factors the Radio Manufacturers Association 
has standardized interlaced scanning with a frame-frequency of 30 
per second and a field-frequency of 60 per second. 


Motion picture film is one source of program material for television. 
With electronic scanning methods it is usual to project an image of 
the film moving or stationary on to some element of the electronic 
translating device. This may be accomplished by the use of an in- 
termittent type of projector, a continuous projector having an op- 
tical intermittent, or a system in which the film moves continuously 
with a compensating motion of film-image and scanning. The par- 
ticular method used is partly determined by the type of electronic 
scanning device. The use of 24-frame motion picture film to produce 







FIG. 5. Diagram illustrating the 3:2 ratio of pull-down 
periods in a special television film projector. 

30-frame television with interlaced scanning presents certain special 

In using an Iconoscope as the electronic translating device it has 
been customary to use an intermittent type of projector. By utilizing 
the storage properties of an Iconoscope, the film-image may be pro- 
jected on to the photosensitive mosaic during the time between the 
completion of one field scanning and the beginning of the next. 
Scanning then may take place and electrical signals may be obtained 
from the mosaic while it is dark. Since the field scanning-frequency 
is at the rate of 60 per second, this means a short period of projection 
60 times a second and of a duration of approximately Vsoo second. 


With 60 projections per second we may hold one frame for three pro- 
jection periods 3 /eo second; the next for two projection periods 
Veo second; the next for three projection periods 3 / 60 second; the 
next for two projection periods. . . . Thus by a 3 : 2 ratio of pull- 
down periods in an intermittent and by the use of a shutter that is 
open only during the vertical return time of the scanning, we may 
derive program material for a 30-frame television system from 
standard 24-frame sound motion picture film, retaining the standard 
film speed. This 3 : 2 ratio of pull-down periods is illustrated diagram- 
matically by Fig. 5. Fig. 6 is a photograph showing two television 
film projectors having these characteristics. 


In order to verify previous conclusions regarding the relative pic- 
ture detail capabilities of a 441 -line television system and home mo- 
tion pictures, a test-target was photographed and reproduced on 
35-mm., 16-mm. and 8-mm. film. A second purpose of making these 
films was to determine the merits of the several film sizes as sources 
of television program material. 

The test- target used in making the films consisted of twelve sub- 
stantially identical major squares arranged in three horizontal rows 
to form a rectangle having a 4 : 3 aspect ratio. Each major square in- 
cluded four minor squares of equal size but different patterns. Each 
major square contained a complete vertical wedge of thirteen tapered 
bars (7 black and 6 white) which started in the upper right-hand minor 
square with a resolution calibration of 100 "resolution bars" and in- 
creased to 200 at the bottom at that minor square. The wedge con- 
tinued in the lower left-hand minor square with 200 at the top and 
300 at the bottom. The bars of the wedge were slightly curved so 
that a linear relation between distance along the wedge and resolu- 
tion could be obtained, facilitating intermediate readings. The hori- 
zontal wedge was similar, beginning with 100 at the left-hand side of 
the upper-left minor square and finishing with 300 in the lower-right 

The area surrounding the wedge in the two lower minor squares 
of each major square was divided into four smaller areas which were 
cross-hatched to produce the effect of different halftones from black 
to white. 

The test-films were not intended to show the maximum resolution 


capabilities of the film but to indicate the picture detail obtained 
through present commercial methods for providing duplicate films. 
The 16-mm. and 8-mm. films were made from the 35-mm. negative 
by means of an optical reduction printer. Two 16-mm. and two 8- 
mm. prints were made. One print of each was made with the custom- 
ary processing to give the proper halftone reproduction. The other 
prints were made to accentuate the detail in the wedges at some sacri- 
fice in halftone gradation. 

Each of the five films was separately used to produce a television 
image by projecting the test pattern on each film on to the mosaic 
of an Iconoscope in an experimental 441 -line television system. The 

FIG. 6. Two special television film projectors. 

video-frequency band employed by this system was from 30 to 3,500,- 
000 cycles, and the single side-band transmission this band-width is 
well within the channel limits that have been tentatively assigned for 
television broadcasting. For each of the five films a photograph was 
taken of the television-image reproduced on the screen of the Kine- 
scope. These photographs are shown in Figs. 7, 8, 9, 10, and 11. Fig. 
7 shows the result obtained from the 35-mm. film. Figs. 8 and 9 illu- 
strate the images secured from the 16-mm. film and Figs. 10 and 11 
give the corresponding results with the 8-mm. film. 

It will be noted that there is a slight reduction in detail from the 
image reproduced from the 35-mm. film to that obtained from the 



FIG. 7. Television image obtained from a test-chart 
on 35-mm. film. 

FIG. 8. Television image obtained from a test-chart on 
16-mm. film with special processing. 

Feb., 1939] 



FIG. 9. 

Television image obtained from a test-chart on 
16-mm. film with normal processing. 

FIG. 10. 

Television image obtained from a test-chart on 
8-mm. film with special processing. 



[J. S. M. P. E. 

16-mm. films. The loss in picture detail when the -8-mm. films are 
used is, however, quite serious. 

From these tests it seems reasonable to draw the following con- 
clusions: In picture-detail capabilities a 441 -line television system 
compares favorably with 16-mm. home movies. If motion picture 
film is used to provide television program material, satisfactory re- 
sults may be expected from 35-mm. film; a slight loss in picture-de- 
tail will result from the use of 16-mm. film, and the resolution ca- 
pabilities of a high-definition television system will not be utilized if 
8-mm. film is used. 

I I I I I 

! ,*i iaaa 

i P I 4^*1 I 

FIG. 11. Television image obtained from a test-chart on 
8-mm. film with normal processing. 


In motion picture work studio lighting and make-up technic are 
dependent upon the color-response characteristics of the film. In 
television the spectral response characteristic of the Iconoscope con- 
trols these factors. This characteristic of an experimental Iconoscope 
is shown in Fig. 12. As indicated by the curve this Iconoscope gave 
maximum sensitivity in the blue end of the spectrum. The most 
desirable Iconoscope spectral characteristic for a given application 
is dependent upon the light-source used to illuminate the scene. 
An Iconoscope having the characteristic shown in Fig. 12 tends to 
compensate for the high red output of the incandescent lamps used 

Feb., 1939] 



in studio lighting. For outdoor pick-up work a characteristic more 
nearly approximating that of panchromatic film is desired. The 
spectral characteristic of the Iconoscope can be varied to a consider- 
able extent by the sensitization procedure employed. Various spec- 
tral-response characteristics obtained in experimental Iconoscopes 
have indicated that characteristics can be provided that are com- 
parable to those of panchromatic and other films. 


The high-intensity arc commonly used as a light-source for motion 
picture projectors produces an image that has satisfactory black-and- 
white characteristics. In the initial stages of cathode-ray television 

FIG. 12. Spectral characteristic of an Iconoscope. 

development, so many serious limitations were present that the green 
color of the image reproduced on a willemite screen was not con- 
sidered to be particularly undesirable. As television development 
progressed and picture-detail and screen brightness improved, the 
green color of the reproduced image became more objectionable and 
development work on luminescent materials to produce a black-and- 
white image was started. Kinescopes having luminescent screens 
giving black-and-white pictures of adequate brilliance are now a com- 
mercial reality. In Fig. 13 the emission spectra of two screen mate- 
rials are shown. Screens of both materials will be judged as white 
if viewed separately, but when compared one to the other one will be 
called blue-white and the other ivory-white. Individual opinions 



[J. S. M. P. E. 

vary greatly as to which is the best white for television screens since 
the apparent whiteness of a television image is influenced by such 
factors as the image brightness and the background lighting in the 
room in which the image is viewed. One thing is certain, and that 
is that purchasers of television receivers will demand substantially 
black-and-white images. 


Those engaged in motion picture work are quite familiar with two 
terms that recently have been given serious consideration in television, 
i. e., gamma and range. Three typical characteristic curves of pic- 
torial reproducing systems are shown in Fig. 14. Curve (a) is for a 

FIG. 13. Emission spectra of two screen materials. 

contrast or gamma of unity, while curves (b) and (c) are for a gamma 
of 0.5 and 2.0, respectively. The ranges available for the image and 
ranges of the object that the system can cover are indicated in the 
figure. In black-and-white motion picture technic, it has become 
standard practice to make the overall object-to-image contrast be- 
tween 1.4 and 2 in order to compensate for the lack of color. Tele- 
vision is also a monochromatic system, and it therefore seems de- 
sirable to follow the experience of the motion picture industry and 
produce television images with a similar increase in contrast. 

The "object brightness vs. output signal" characteristic of the 
Iconoscope has been measured and found to vary with the amount 
and distribution of light in the object. However, it may be stated 
that in general the Iconoscope is a low-gamma device the value 
varying between 0.7 and 0.9 for most of the cases encountered in prac- 

Feb., 1939] 



tice. The Kinescope has an inherent contrast or gamma of ap- 
proximately 1.5 but the saturation effect in the screen material re- 
duces this to the neighborhood of 1.2. The overall gamma of the 
television system, so far as the Kinescope and Iconoscope are con- 
cerned, is therefore substantially unity. This is quite satisfactory 
when motion picture film is used to provide program material, since 
the contrast has already been raised to a proper value by an ex- 
perienced photographer. An overall gamma of unity is probably in- 
sufficient when transmitting scenes picked up directly by the Icono- 
scope. In motion picture work gamma is controlled by the film 

10,000 :i 

10 100 1000 



FIG. 14. 

Three typical characteristic curves of pictorial reproduc- 
ing systems. 

emulsion and the method and time of development. In television any 
desired gamma can be obtained by varying the characteristic of one 
of the signal amplifiers in either the receiver or transmitter. 

Although the brightness range in television images may be limited 
in several portions of the system the present practicable limit is in the 
Kinescope. The bulb shape of the Kinescope is determined by the 
physical characteristics necessary to withstand atmospheric pressure. 
For this reason the screen of a conventional Kinescope has a certain 
curvature, thus permitting illuminated parts to throw light directly 
on non-illuminated parts. Reflections may occur also from other 
portions of the inner surface of the bulb. In addition to these re- 
flections, a certain amount of light is totally reflected from the glass- 


air boundary and introduces a reduction of range in details by hala- 
tion. These effects have been reduced by blackening the inside walls 
of the bulb and by introducing a small amount of light-absorbing 
material in the glass wall. Conventional Kinescopes have an avail- 
able range of about 50 to 1 for large areas and 10 to 1 in details. Ex- 
perimental Kinescopes have been built in which the luminescent 
screen is deposited on a thin sheet of glass which is mounted inside a 
transparent glass bulb. Such tubes are capable of a considerably 
greater range between large areas and in details. 


1 ENGSTROM, E. W.: "A Study of Television-Image Characteristics," /. Soc. 
Mot. Pict. Eng., XXII (May, 1934), p. 290. 


MR. CRABTREE: When televising an outdoor subject, what is the threshold 
light-intensity necessary for reproduction, as compared with that necessary when 
photographing with an f/2 lens in combination with the high-speed film emul- 
sion we now have available? 

MR. BEERS: With various standard and special pick-up tubes, we can get 
pictures under any lighting conditions in which you can take pictures on film. 

MR. CRABTREE: In other words, you can reproduce satisfactorily a foot- 
ball game about half an hour after sunset on a rainy day? 

MR. BEERS: Yes. We have obtained recognizable pictures in which the 
subject had a surface brightness of 1 or 2 foot-candles. 

MR. CARVER: I do not understand whether you have a flicker blade or not or 
whether it is or is not necessary. 

MR. BEERS: There is no flicker blade, as such. A flicker blade is not neces- 
sary in television, due to the way in which we reconstruct the image. We pro- 
duce on the end of the tube a certain number of images a second, and that con- 
trols the flicker. Nothing in the projector has anything to do with the manner 
in which the images are actually reproduced. 

MR. CARVER: What do you do when the film is being pulled down? There 
is no picture on, and there must be a dark space. 

MR. BEERS: You are actually seeing the picture when the film is being pulled 
down. During the pull-down we scan the electrical image that remains on the 
mosaic of the Iconoscope. That is when we see the image at the receiver. The 
picture is projected when nothing is seen at the receiver. That is the interval in 
which we transmit the synchronizing signals. 

We have two choices in television. One is to attempt to scan the picture on 
the mosaic of the Iconoscope during the time the picture is actually being pro- 
jected there. That means then that we have to pull down the next frame of film 
during the time we transmit our scanning signals, which is approximately Vsoo 
of a second. That imposes some physical requirements on a projector we have 
not been able to meet. We have not been able to conceive of a projector on which 
the frame can be pulled into place in 1 / 8 oo second without tearing the film. The 


easier way is to pull the film into place in the gate during the long interval of time 
and to project it on the Iconoscope mosaic during the short time interval; and 
then to scan it, while the optical image is no longer on the mosaic, using the elec- 
trical image that is stored there. 

MR. FRIEDL: With relation to standardization, it appears from these papers 
that standards are set on the basis of electronic scanning, determined by frame 
frequency, screen persistency, halation, and so on all of which result in the broad 
frequency-band which we can admit is a limitation to the general application of 
direct television. 

Reference was made to mechanical systems in England and the speeds with 
which these systems operate. Can someone throw some light on the question of 
mechanical systems vs. the electronic systems? 

MR. GOLDSMITH: The electronic systems offhand seem to be most appro- 
priate because electrons are weightless and are readily controlled in flight and 
form a sort of "air-brush" for painting pictures which can be moved rapidly and 
readily. The only mechanical system that seems to be seriously considered 
commercially today, at least in England, is the one Mr. Kaar mentioned, the 
Scophony system, in which essentially there is a storage capacity, because of a 
diffraction phenomenon of standing waves of supersonic frequency in liquid, 
actuated by a vibrating quartz crystal. In this system one may scan a half line 
at a time (about 200 picture elements) . 

This system, however, as Mr. Kaar pointed out, employs a motor running at 
some 30,375 revolutions per minute for the high-speed or line deflection of the 
spot, and a smaller motor, running at a lower speed, for the frame scanning, two 
mirror systems, the supersonic cell, some lenses, and a mercury-vapor capillary 
lamp for the light-source. The picture produced is 18 X 24 inches in size. 

The competitive devices in England are, for example, the Phillips receiver 
which produces an 18 X 24-inch picture by projection from approximately a 3-inch 
projection type cathode-ray tube. 

The prices on the British market today are $850 for the Phillips receiver pro- 
ducing the 18 X 24-inch picture, and something over $1100 for the comparable 
Scophony receiver, but nobody has given reliable data as yet as to the relative 
performance, life, and economics. 

The receivers in England run in the price range from $125 to $150 (for the pic- 
ture only) in a chair-side type. Receivers for larger pictures run up to $300 or 
$400, with top figures of $1200 for very large pictures (18 X 24 inches) with 
sound and all sorts of extra attachments, phonographs, and the like. 

MR. BEERS: If it were economically possible to use 24 frames in television it 
would be done. It is theoretically possible, but the increased amount of filtering 
and shielding necessary in the receiver to make it perfectly satisfactory from the 
standpoint of eliminating the moving images resulting from the 60-cycle power- 
supply system make it economically impracticable. 

MR. ROBERTS: When scanning 24-frame motion pictures at 60 or 30 cycles, 
do you get any time-distortion in the presentation of the picture? Would there 
be any unexpected effect as a result of seeing one frame longer than the one 
before it? 

MR. BEERS: We have noticed no more distortion than is normally noticed in 
motion pictures. 


MR. CRABTREE: Do you think the trend will be to record directly by means 
of television scanning, or that the subjects will be photographed on motion pic- 
ture film previously to scanning? What are the relative merits of the two proc- 
esses direct scanning and transmission at the scene, as against photographing 
the scene and then bringing the film to a central transmitting station? 

MR. BEERS: That is a program problem. Either can be done. The scene 
may be taken on motion picture film and then converted into television program 
material; or, as you know, we have a mobile unit, which can be taken out to the 
scene and there televise it and transmit its picture directly by relay to the trans- 
mitting station. 

MR. CRABTREE: When we met in New York we gained the impression that 
the actors hi the studios had to work under high temperatures, with fans blowing 
on them and the make-up melting on their faces. In other words, it seemed to be a 
terrible ordeal to be a television actor. Would it not be simpler to photograph 
the scene and then to transmit it? 

MR. GOLDSMITH: That condition has been markedly improved. 

MR. BEERS: The sensitivity of the electronic pick-up device is being con- 
stantly improved, and as it is improved, of course, this high-temperature condi- 
tion that you mention is reduced. From what little contact I have had with 
motion pictures, I am not sure that conditions in that respect are so vastly differ- 
ent. The advantage in motion pictures is that you can shoot a scene and then 
take time to cool off; but in television, if we wish to keep a continuous program 
on the air, the actors have to stay under the lights and suffer. However, as I 
said, as the sensitivity of the pick-up device is improved the heat to which the 
actors are subjected will decrease. 

MR. SCHLANGER: Am I to understand that the television picture is equal in 
quality to a 16-mm. picture, projected with a 250-watt lamp and of comparable 
size and vie whig distance? 

MR. BEERS: From the standpoint purely of picture detail they would be 
comparable. I stated that the film was processed to produce duplicate films. 
If you take standard home motion pictures on reversible film, you will have some- 
what better detail, but with ordinary commercial processing of duplicate films, 
I think that the picture detail of the two will be comparable. 



Summary. The binaural effect, while of great importance in our day-to-day life, 
has been an unexplored field in our conventional monaural sound motion picture 
which, despite our other technical advances, remains incapable of the quality called 
sound ' ' perspective. ' ' 

To achieve the missing quality, it is important that controllably variable perspective 
effects be attainable for the release print from an original having different perspective 
quality. This is necessary not only to make the sound recorded on a three-walled set 
simulate the sound from a six-sided room, but also to make the recorded sound corre- 
spond satisfactorily with the view portrayed by the camera. 

A new system is described that not only fulfills these fundamental requirements, but 
also is capable of controllably producing at will the various perspective and quality- 
change effects in a simple dubbing operation from a source having no perspective 
characteristics such as a conventional monaural sound-track. The new method may 
be introduced step by step into our present production system without material obsoles- 
cence of either films or equipment. 

There is a very simple test that anyone can make that should 
conclusively answer the question, "Why binaural?" As someone 
speaks to you, hold a finger to one ear so as to prevent sound from 
entering that ear. You will notice a marked difference in the sound; 
it now seems hollow, and, if you close your eyes, the voice that was 
so intimately near but a moment ago has changed and now seems to 
have a different aspect which causes it to appear indistinct; and, 
you are now somewhat confused as to the true location of the speaker. 
If, with your eyes still closed, you remove the obstructing finger so as 
to hear normally through both ears, the voice of the speaker again 
becomes distinct and takes on all the characteristics that you regard 
as natural ; and your speaker again seems human to you. 

Despite the fact that we are aware that monaural systems are 
quite incapable of that quality called perspective, all our commercial 
sound recording and reproducing systems in use in motion pictures 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 3, 

** New York, N. Y. 


140 W. H. OFFENHAUSER, JR., AND J. J. ISRAEL [j. s. M. p. E. 

today are monaural or one-eared systems. Technical development 
of monaural systems has been pushed ahead by the industry at full 
speed; the success of these efforts has been reflected in renewed 
energy in the development of the newest advance which no doubt 
will soon take its place commercially in the industry binaural 
sound recording and reproduction. Binaural recording, like stere- 
oscopic pictures, has a long history of achievement as well as dis- 
illusionment. The difficulty encountered in approaching both sub- 
jects has the same character; it is necessary for us to understand 
human reactions before we can attempt even to consider technical 
solutions. This analysis of the human phase at first glance seems 
simple ; yet, closer inspection reveals that the more we look into the 
subject, the less we appear to comprehend. 

Before any methods or apparatus can be considered, it is necessary 
to approach the problem in the manner in which we approach any 
problem of evaluation; we must first determine our hypotheses and 
our axioms; and only after these are fully decided upon may we 
approach our theorems. This must be done with fear and trem- 
bling ; every step in the formulation of the hypotheses and axioms 
must necessarily involve compromise as it will be found that no two 
workers in the field can agree completely upon either the premises or 
the objectives. 

We must leave to the psychologists the problem of evaluation of 
human reactions. In every step of our reasoning we must keep in 
mind the fact that a motion picture audience is a group of customers 
who take nothing tangible home with them despite the fact that they 
pay something tangible for what they receive. It is the purpose of 
the motion picture to create an illusion by whatever means, and the 
most successful motion picture is the one that creates the best illusion. 

Our psychologists have pointed out for centuries that reality and 
our concepts of it may have little to do with one another. We have 
been told repeatedly that only the abstract can be perfect : the more 
real (in the sense of physical reality) a thing becomes, the more notice- 
able are its flaws. The same may be said to be true of motion pic- 

This point has been amply demonstrated time and again. In the 
recording of sound, for example, we would not always care to have 
the noise of a collapsing building reproduced for us in our theaters at 
its original volume, particularly if, after the building collapsed we 
wished to hear dialog between two of our principal characters. The 

Feb., 1939] BlNAURAL RECORDING 141 

perfect picture would be one that would create the illusion of the 
falling building without causing the physical discomfort that would 
result if we were to hear the noise in all its original intensity. 

In motion pictures it is the illusion produced by the facile and 
artistic combination of both picture and sound that is the desideratum 
of a "good show." This is forcefully pointed out when we consider a 
hypothetical case that could well take place. Suppose one were to 
make a sound record, without picture, of the waves breaking on the 
beach at Atlantic City. For the sake of illustration let us boldly 
assume that we are able both to record and reproduce this sound 
without any loss of fidelity whatever. We will project this sound 
under ideal conditions for a group of Iowa Agricultural College 
students, most of whom have never been to the seashore. What will 
be the reactions of this audience after a long afternoon spent in the 
hot sun studying Japanese beetle control ? There is only one answer : 
our recording accomplished with such technical perfection is nothing 
more than a meaningless noise that is at first quite boring, and, after 
a few seconds, a plain nuisance from which our students will seek 

Binaural recording is something that we ought to have in motion 
pictures today. It will immeasurably enhance the illusion when 
properly applied, as has been indicated by the remarkable sound 
illusions produced by the engineers of the ERPI and allied groups. 
A motion picture director with an imaginative mind would revel in the 
delightful possibilities of creating illusions with even today's com- 
mercial motion picture and today's demonstrated results in binaural 
sound transmission. With stereoscopic color pictures and binaural 
recording, our director could well indulge in an artistic orgy. 

Motion pictures with binaural sound can hardly be considered 
visionary today: many years before sound was introduced com- 
mercially into our motion picture theaters, patents had been granted 
to far-seeing inventors on the combination of motion pictures with 
binaural sound. The binaural patent that is the forerunner of them 
all is that of Rosenberg, applied for in Great Britain on October 25, 
1911 (Brit. Pat. No. 23,620). Rosenberg's appreciation of the 
problem is truly remarkable and his clarity can well be considered a 
model for others to follow. 

It is doubtful that Rosenberg's reduction to practice consisted in 
much more than the filing of his patent application. Surely there 
was little that he could do at the time in making models of his in- 


vention. The vacuum tube was practically unknown outside of a 
very few research laboratories. The quality possible with existing 
microphones and loud speakers was such as to discourage any inven- 
tor with far-reaching ideas. It is indeed a tribute to the man's con- 
fidence in his ideas that he prosecuted his patent to a successful con- 
clusion, and a tribute to the British Patent Office that his patent was 
passed to issue. 

If one reviews the advance of the art since Rosenberg, it does seem 
fair to say that most inventions since then have been primarily 
adaptations of currently existing mechanisms to the art as disclosed 
by him. There has been little of theoretical value added unless it be 
the concepts of Kuechenmeister dealing with the delay effect. (Brit. 
Pat. No. 238,372; applied for Aug. 12, 1924.) This currently popu- 
lar concept as applied to binaural recording on film is shown in 
Kuechenmeister British patent 258,864, which had a convention date 
of Sept. 22, 1925. Certain other inventions may be classified as 
frequency characteristic variation; still others have shown multi- 
plicities of microphones, multiplicities of amplifiers, multiplicities of 
recording means, and multiplicities of loud speakers ; others disclose 
dummy heads and their equivalents with microphonic ears. All 
these things have been combined with motion pictures, television, 
radio, phonographs, broadcasting, as well as an almost infinite variety 
of other things worthy of passing mention. In the motion picture 
field, these have even been combined with "wandering" sound- 
tracks and other inventions of similar nature. 

The improvement that has occurred in the art of motion picture 
production since sound was first introduced commercially, can be 
summarized briefly as an improvement in technic. In the physical 
stages of production, there exist both shooting and editing, and it can 
truly be said that today a picture is made in the cutting room. The 
editing aspect is almost daily acquiring greater and greater im- 

The addition of anything new to sound motion picture production 
must consider the adaptability of the new element to the editing 
process as well as to the shooting process. If the new added element 
involves little or no added complexity in the shooting process, so 
much the better. Stage time costs money as all producers know 
only too well. If the new added element further involves but a small 
added complexity in the editing process, it can be introduced readily 
provided the scheduled editing time and expense are not unduly 

Feb., 1939] BlNAURAL RECORDING 143 

increased. This is important since the present tendency is to limit 
stage operations and to delegate more and more work to the editing 
process. H. G. Tasker's description of the production process given 
to the Society at the last Hollywood meeting points out indirectly the 
importance of editing when the procedure he described is compared 
with what we now consider the antiquated methods of 1928 and 1929 
when pictures were, for the most part, made on the shooting stage. 

At first glance, the application of binaural recording to motion 
pictures would seem to hold unknown terrors for the production 
supervisor. It would seem that there would be no assurance that the 
desired effect could be produced at all even if it were accurately de- 
fined; and, for that reason, shooting delays would seem almost 
certain to occur due to the introduction of the new technic, result- 
ing in prohibitive shooting costs. 

Let us consider such a simple scene as that of a talking actor passing 
through a doorway. Our actor performs in a three-walled set located 
on a shooting stage. It is difficult to record scientifically "perfect" 
sound for such a sequence. In the first place, the sound heard must 
correspond with the picture seen; the picture is dependent upon 
camera location and lens size. In the second place, even assuming 
that we could make the sound and picture correspond, it would still 
be impossible to produce by usual straightforward methods a sound 
record having the characteristics of a six-sided room when the record- 
ing is actually made in a three- wall set. A director would "throw 
up his hands" as soon as the actor started through the doorway; 
the extremely rapid swinging of the microphones suspended on the 
boom necessary to produce a suitable acoustic spatial effect would be 
entirely impracticable in a set of present-day construction. Under 
the circumstances, it is rather impracticable to attempt scientifically 
"perfect" recordings especially when it is an illusion that we are 
trying to produce, and we are already aware that reality and our con- 
cept of it may differ radically. 

The tricks of the sound-effects men are a case in point. It is indeed 
a revelation to the average movie-goer to view the various gadgets 
used by these artists in the production of their convincing sound 
illlusions. In spite of our innate desire for scientific truth, we do not 
exhibit to the public gaze the props that form such an important 
part of our artistic legerdemain; our attitude, rather, is to produce 
the best illusion we know how and to ignore entirely the means of its 
production. The mechanical contrivances backstage would not add 

144 W. H. OFFENHAUSER, JR., AND J. J. ISRAEL [j. s. M. P. E. 

to the illusion if they were exposed to public view; we go even so far 
as to conceal them willfully. 

Why, then, in the case of an actor going through a doorway, is it 
necessary for us to swing microphones at a prodigious rate merely to 
create a scientifically "perfect" recording, when it is possible not 
only to produce the desired illusion by far simpler means but also to 
do it without any especially serious change in shooting technic? 
This is all the more forcefully pointed out when it is realized that our 
scientifically "perfect" recording can at best produce only the wrong 
illusion, because we are recording in a three-walled set. 

Suggestions have appeared in the prior art 1 - 2 ' 3 - 4 from time to time 
that a procedure is possible for moving sound around in reproduction 
without any movement of the sound on the shooting stage. A 
typical instance is Jones in U. S. Pat. No. 1,855,146 and the various 
divisions of the invention there disclosed. In the vernacular, Jones 
may be said to disclose "the wriggling of microphonic ears in a dummy 
head." Regardless of the means, there has been little serious con- 
sideration of this feature of moving sound around artificially in test 
and other stereophonic and binaural films that have been exhibited as 
samples of the binaural art. If the binaural art is to be fitted into 
everyday sound motion picture production, it must consider for the 
release print the production of acoustic effects that were not produced 
on the shooting stage. 

Rosenberg clearly described the requirements:" the necessity for 
communicating to the spectator an impression of constant coincidence 
between the actual and the visually apparent sources of a train of 
sounds as reproduced is due to the fact that . . . the perfection of the 
illusion will be impaired unless those sounds which represent the 
voice of the performer are at each instant made to appear as if they 
actually proceeded from whatever spot the speaker is himself visually 
represented as momentarily occupying." 5 

Jones 6 has suggested that the apparent location o a sound in space 
can be shifted about by the "wriggling" of the microphonic ears in 
the dummy head that he disclosed. His theory is based on the delay 
concept that Kuechenmeister 7 has aptly described "means intended 
to convert into sound the record optically produced on the talking 
film are so arranged with respect to the said record on the film that 
the sound reproducer or reproducers connected to the said means will 
repeat the sound at a small interval of time." Kuechenmeister did 
describe this delay effect as a phase-difference and expressed his 

Feb., 1939] BlNAURAL RECORDING 145 

phase difference as "being about Vso to Vs of a second." Jones 
describes his delay effect as a phase-difference also, only he measures 
his delay in what he calls "sound-inches"; a coined term to indicate 
the time-interval required for sound to travel a distance of one inch. 

Investigators in the field are not agreed as to whether phase- 
difference has something to do with the problem or not; the point at 
issue seems to be the definition of phase-difference as applied to this 
particular problem. A number of investigators are quite definite and 
state with apparent assurance that phase-difference has nothing 
whatever to do with the case and that it is amplitude-difference that 
is the crux of the question. Other investigators state with apparently 
equal assurance that phase-difference is the crux of the question, 
despite the fact that much of the prior art has accepted the ampli- 
tude-difference theory. Still others straddle the fence and propose 
the conversion of phase-differences into amplitude-differences, 
particularly in the low-frequency portion of the audio spectrum. 
To an impartial student, such a condition is indicative of lack of 
agreement upon hypotheses. As Mark Twain put it, "An argument 
arises when people use the same words to describe different things or 
when they use different words to describe the same thing." 

It looks as if we engineers are stepping out of our field a bit at this 
stage in attempting to define phase-difference. We are not specific as 
to whether our aural impressions are air-borne through a common 
medium or whether the binaural impressions are separately conveyed. 
In the motion picture business we are of course interested in the 
former; the research man has primary interest in the latter as a step 
in the fuller understanding of the former. It is not our privilege to 
decide how the two impressions received at the two ears are integrated 
in the brain. That is the province of the physiologist and the psychol- 
ogist and we are getting ourselves into a limitless morass unless we 
approach this problem in the same scientific manner in which we 
approach our other technical problems. 

Our purpose is to create an illusion and the most successful motion 
picture is the one that creates the best illusion. Let us then put aside 
for the time being, at least, the question of phase-difference vs. ampli- 
tude-difference and do a bit of listening with our ears. When we 
have once decided what creates the illusion we want, let us then again 
attempt to analyze the means of its production, after the psychologists 
have told us what we are now in dire need of knowing. 

There are, of course, a number of points of agreement. We can 


agree that two-eared hearing as we experience it in everyday life is 
better than one-eared hearing. We can also agree that in one-eared 
hearing, reverberation plays an important part in conveying the 
depth impression. We can also agree that if we have one sound 
record and reproduce it as Kuechenmeister did through two chan- 
nels, controlling the delay of one cliannel with respect to the other, 
certain effects are produced that to many persons are pleasing. We 
can also agree that the practical demonstrations of auditory per- 
spective given by the ERPI engineers produced sound results that 
were as desirable as they were startling. All that remains is to 
apply these effects to the production of sound motion pictures in a 
practicable and economic manner. 

If we ignore for the moment reverberation effects, it can be fairly 
said that it is our present practice and a very desirable one to 
record all our sound with relatively close microphone placement. It 
is in this manner that we are able to reduce extraneous noise to a 
minimum. If, then, we can continue so to record and later produce 
in the dubbing room the desired perspective and spatial effects with- 
out any increase in noise-level other than that due to the addition of 
the usual re-recording step in the production of the final print, we 
then have a system which from an engineering viewpoint is ideal, in 
that it allows the highest signal-to-noise ratio and also the attainment 
of the desired dramatic perspective and spatial effects in the dubbing 
room, where the cost of retakes is so small relative to those of the 
shooting stage that it is possible to avoid compromise with quality in 
the sound portion of the presentation. 

With the system to be demonstrated, it is possible not only sub- 
stantially to achieve these desiderata but also to produce quite 
similar effects using only a standard single channel in recording, and 
nevertheless effecting the perspective control in the dubbing room 
much in the manner of a binaural recording. As is to be expected, 
the quasi-binaural system, as we may call it, is not quite as con- 
vincing as the full binaural system. When the illusion is aided by the 
picture, however, it is doubtful whether the average audience would 
notice the difference, particularly if the quasi-binaural films were 
released in the transition period from monaural to binaural. 

The change from monaural to binaural films in reproduction can be 
made without difficulty. In projecting binaural films, we can select 
either one track or the other or possibly mix the two by scanning 
both with the same light-beam in a conventional monaural projector. 

Feb., 1939] BlNAURAL RECORDING 147 

Thus a film printed for binaural release can be projected satisfactorily 
on a conventional projector and at the same time be suited to pro- 
jection on a binaural projector. There is no technical reason why all 
films should not be printed for binaural release. 

In the production studio, the change to binaural can be made with 
equal facility. Since it is possible to dub a monaural recording for 
binaural release, films on the shelf are not made obsolete merely 
because a new improvement in sound recording has arrived. 

The stage-shooting technic for binaural recording requires no serious 
change from the present technic since the perspective control portion 
of the process is to be effected primarily in the dubbing room. On 
the sound-stage, the sound may be recorded much as it is today with 
the possible modification that somewhat less microphone manipula- 
tion may prove desirable. As the experience gained in production 
increases, the advantageous deviations from the present procedure 
may be studied and later introduced as their peculiarities become 
better understood. The change to the new system requires no drastic 
revisions of either operating technic or apparatus other than the 
eventual introduction of the necessary second channel. 

There seems to be but little agreement upon the acoustic effects 
desired. If we consider the requirements as defined by Rosenberg 
we can, in all likelihood, agree that left-right movement is desirable ; 
that some convincing impression of the distance of a sound-source 
from the scene represented is likewise desirable; and that possibly 
some impression of the directness with which the sound is presumed 
to approach the listener is desirable. On the other side of the Atlan- 
tic, this last is known as the "round- the-corner" effect. As in the 
past, our procedures will, no doubt, best be worked out by rule of 

The system to be demonstrated is not limited to motion pictures; 
it may be applied in any field where it is desired to transmit im- 
pressions by means of sound. Some of the effects that have been 
produced with the system include variation of the apparent recording 
room size from very small, say, 1000 cubic feet, to very large, say, 
500,000 cubic feet. Also important is the simultaneous yet inde- 
pendent movement in reproduction of one sound-source with respect 
to another. Essentially independent left-right movement as well as 
close-up and distant perspective has also been attained. All these 
effects were produced in reproduction without movement of the 
actual sound-sources with respect to the microphones. In motion 

148 W. H. OFFENHAUSER, JR., AND J. J. ISRAEL [j. s. M. p. E. 

pictures, the application of such a system can appreciably increase 
editing latitude and improve dramatic effectiveness. 

The authors then proceeded to demonstrate the system. A conventional single- 
channel disk reproducing turntable was connected to the perspective-control device at 
the rear of the room. Two channels from this device fed independently to two loud 
speakers placed side by side on a platform directly before the audience. No movement 
of the speaker with respect to the microphone or the surroundings occurred when the 
record was made; the perspective or binaural effect was produced entirely by the 
manipulation of the prespective control in the rear of the room. The sounds appeared 
to move from one side of the room to the other, upward and downward, or backward and 
forward, as the controls were manipulated. 


1 BEERS, G. L.: U. S. Pat. 2,098,561 (Nov. 9, 1937). 

2 HALSTEAD, W. S. : U. S. Pat. 2,022,665 (Dec. 3, 1935). 
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4 PATTERSON, W. M.: U. S. Pat. 1,994,920 (Mar. 19, 1935). 
DOUDEN, W. L.: U. S. Pat. 2,124,030 (July 19, 1938). 

6 ROSENBERG, A.: Brit. Pat. 23,620 (Oct. 25, 1911) (application date). 

6 JONES, W. B. : U. S. Pat. 1,855,149, p. 3, line 36 et seq. 

7 KUECHENMEISTER, J. : Brit. Pat. (Aug. 12, 1924) (application date). 

(Patent dates listed are dates of issue unless otherwise specified.} 


STEWART, G. W.: "The Intensity Factors in the Binaural Localization of 
Sound," Phys. Rev., Series 1, 34 (1912), p. 76 (abstract). 

"The Significance of Intensity-Sum in Binaural Localization," Phys. Rev., 
Series 2, II (1913), No. l,p. 72. 

"The Character of Interaural Sound Conduction by Binaural Beats," Phys. 
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"Phase Relations in the Acoustic Shadow of a Rigid Sphere; Phase Difference 
at the Ears," Phys. Rev., Series 2, IV (1914), No. 3, p. 252. 

"The Intensity Factor in Binaural Localization and an Extension of Weber's 
Law," Phys. Rev., Series 2, IX (1916), No. 4, p. 338 (abstract). 

"The Functions of Intensity and Phase in the Binaural Location of Pure 
Tones. An Experimental and Theoretical Investigation of Binaural Beats," 
Phys. Rev., Series 2, IX (1917), No. 6, p. 338 (abstract). 

"Binaural Beats," Phys. Rev., Series 2, IX (1917), No. 6, p. 502. 

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IX (1917), No. 6, p. 509. 

"The Theory of Binaural Beats," Phys. Rev., Series 2, IX (1917), No. 6, p. 

Feb., 1939] BlNAURAL RECORDING 149 

"The Functions of Intensity and Phase in the Binaural Location of Pure 
Tones," Phys. Rev., Series 2, XV (1920), No. 3, p. 248 (abstract). 

"The Function of Intensity and Phase in the Binaural Location of Pure Tones," 
Phys. Rev., Series 2, XV (1920), No. 6, pp. 425, 432. 

SIMPSON, M.: "Experiments in Binaural Phase Difference Effect with Pure 
Tones," Phys. Rev., Series 2, XV (1920), No. 6, p. 421. 

HARTLEY, R. V. L. : "The Function of Phase Difference in the Binaural Loca- 
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MAXFIELD, J. P.: "Some Physical Factors Affecting the Illusion in Sound 
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FLETCHER, H.: "Auditory Perspective Basic Requirements," Electrical 
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STEINBERG, J. C., AND SNOW, W. B.: "Auditory Perspective Physical Fac- 
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MAXFIELD, J. P.: "Demonstration of Stereophonic Recording with Motion 
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"Pick-Up for Sound Motion Pictures (including Stereophonic)," /. Soc. Mot. 
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HARTLEY, R. V. L., AND FRY, T. C.: "The Binaural Location of Complex 
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MAXFIELD, J. P. : "Some Physical Factors Affecting the Illusion in Sound Mo- 
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"Auditory Perspective" (a symposium), Elect. Eng. (Jan., 1934), pp. 9, 216; 
Bell Syst. Tech. J. (April, 1934), p. 239. 

CHAPIN, E. K., AND FIRESTONE, F. A.: " The Influence of Phase on Tone 
Quality," /. Acoust. Soc. Amer., V (Jan., 1934), p. 40. 


MR. OFFENHAUSER: There is one feature in particular to which we would like 
to call your attention and that is the fact that it is now possible to make the sound 
appear to come from a point some distance beyond the physical limits of the loud 
speakers themselves. This, to the best of our knowledge, has never been accom- 
plished before and is a feature that should open up a new wealth of dramatic 
possibilities through the increase in editing latitude of which we spoke. It is 
particularly significant that this effect can be produced not only by a binaural 
(two-channel) input but also by a monaural input of the everyday variety, as 
has just been demonstrated. Another important fact is that the point from which 
the sound appears to emanate can be shifted about in space at the will of an 
operator even though the original record is of the constant-quality conventional 
monaural type. It is now possible to provide by this method variably controll- 
able perspective in binaural release-prints from any conventional sound-track 
as a source. 

MR. GOLDSMITH: Did the same sound come from each loud speaker? 

MR. OFFENHAUSER: There are two different loud speakers, one for each 
output channel. 

MR. GOLDSMITH: And you control the amplitude and phase relationships 
between them? 

MR. OFFENHAUSER: The turntable over at the left feeds into our apparatus 
at the rear of the room. From the output of the apparatus, the system becomes 

150 W. H. OFFENHAUSER, JR., AND J. J. ISRAEL [J. s. M. P. E. 

what might be termed a conventional binaural system. The particular applica- 
tion of the quasi-binaural system that we have just demonstrated is to provide 
perspective in binaural release-prints in sound that had no such perspective as 
originally recorded. 

MR. GOLDSMITH: You take monaural sound and bring it in modified form to 
two separate speakers which play it back in binaural form. 

MR. OFFENHAUSER: That is correct. The system also permits the use of a 
conventional binaural input which produces other desirable effects not attain- 
able with conventional equipment. 

MR. CARVER: Was someone varying the effects while we were listening? 

MR. OFFENHAUSER: Mr. Israel, at the back of the room. He was manipu- 
lating the controls which produce the effects. 

MR. WOLF: What is the relation between the two acoustic sources? 

MR. OFFENHAUSER: As mentioned in the paper, there appears to be a differ- 
ence of opinion as to whether the effects are a result of phase-difference or ampli- 
tude-difference or both. 

We can offer this as a clue to the answer to the question. In certain tests 
that we conducted with sounds of complex wave-form, we connected the vertical 
plates of a cathode-ray tube across the loud speaker leads of one channel and 
the horizontal plates of the tube across the loud speaker leads of the other channel, 
and then manipulated our controls as we did in the present, demonstration. The 
trace on the tube screen was a straight line which took different angular positions 
on the screen as our controls were manipulated. We obtained substantially the 
same effects demonstrated today, and throughout the variation the trace on the 
screen remained a straight line. Phase-difference would thus appear to be quite 

MR. GOLDSMITH: You are asking that we be aural "guinea pigs," and you 
want to know whether as such we got the effect of distance and of people turning 
their heads, or moving away, or moving forward, or turning toward a reflecting 
wall, and the like. It would be interesting to have the members of the audience 
express their viewpoints, as to whether they got the impression of people moving 
about and turning their heads away from the audience, and whether the effect 
approximated the binaural action. 

MR. CUTHBERT: The effect was very noticeable. There is one point, how- 
ever: How much of the effect was actually due to the directional quality of the 

MR. OFFENHAUSER: Possibly the best answer to that question is in our past 
experience. We made quite a number of extensive tests with all sorts of speakers, 
and as a result we consider it reasonable to expect that these binaural effects 
can be reproduced effectively if each of the loud speakers used will cover the 
area properly as a monaural speaker in the conventional manner. 

MR. GOLDSMITH: You mean, then, that the two speakers will operate satis- 
factorily in the overlapped areas. That would create an acoustic pattern which 
you are shifting about. I noticed a definite change in acoustic quality and a 
decided movement of the voice. I had the feeling that the control was some- 
what overdone in two or three places. There were times when it was handled 
with more care and feeling. I noticed some effects I thought were significant, 
but there were parts, of course, where you were just exaggerating the effects. 

Feb., 1939] BlNAURAL RECORDING 151 

MR. OFFENHAUSER: There is one problem that always arises in connection 
with any binaural sound transmission, and that is the orientation of the listener 
with respect to the sound being transmitted. We will admit that we tried it out 
on you. Since there was no picture, we felt that it would be a good test, because 
if we could produce the illusion with sound alone without the very material aid 
that a picture gives, there would be no question that the illusion produced by the 
combination of picture and sound would be heightened to the point where it 
would be quite satisfactory. 

MR. WOLF: There was definitely no lag between the two channels. 

MR. OFFENHAUSER: We have only one input channel. There is no electrical 
time lag in the system. 

MR. WOLF: It appears to be nothing more than a phase change. 

MR. OFFENHAUSER: Not quite. As we have explained before, it is more 
like a combination of both phase and amplitude control. 

MR. MITCHELL: What difference would it make if the loud speakers were 
separated, one on each side of the room. I think it is customary to assume that 
binaural speakers will be placed quite widely separated. 

MR. OFFENHAUSER: While wide speaker placement has been found by cut- 
and-try methods to be most satisfactory in conventional binaural systems, our 
results seem to indicate no such limitation for this system; in fact, speakers 
placed side by side, as we have placed them here, produce the most, shall we say, 
startling effects? 

MR. GOLDSMITH: Dramatic effects? 

MR. OFFENHAUSER: That is a better description. Of course, in the initial 
public demonstration of a system of this sort we must try to obtain exaggerated 
effects in order that you may leave with some lasting impressions. If we were 
to show this in its true aspect as it would be shown with a picture, the sound 
demonstration without the picture would not be as impressive. That is entirely 
psychological, as you are aware. 

MR. MACNAIR: This paper, on two channel reproduction, emphasizes again 
before the Society that our normal equipment is a one-channel system from 
the sound stage through to the theater, and as such has certain inherent limita- 

I should like to make one appeal, which may seem to many of you here to be 
a purist's appeal. This is on the use of this word "binaural." Sooner or later, 
if this type of reproduction becomes common, the Standards Committee is going 
to be up against the choice of standards and nomenclature and it will ease their 
work if we pay attention to the exact meaning of the word. Normally a bin- 
aural system refers to a system in which the sound is picked up by a dummy 
or something similar with a microphone to replace each ear. The left ear of the 
dummy hears sounds that would be heard by the left ear of an observer in that 
position, and the right ear of the dummy would hear the sound that would be 
heard by the right ear of an observer in that position. 

The word "binaural" has been used to refer to that type of system which, in 
a very strict way, transfers those two channels to a right and left ear of the 
ultimate observer. The characteristic of that system is that the sound that is 
heard by the left ear of the dummy is transmitted only to the left ear of the 


observer, and the sound that is received by the right ear of the dummy is trans- 
ferred only to the right ear of the observer. 

I think it would make our discussion easier if the word "binaural" were left 
for that unique and accurately specified system, and that these other systems, 
which give a sense of motion of the sound, were referred to by some other name. 

MR. OFFENHAUSER: In all the earlier patents and scientific publications such 
as in the Physical Review, the term "binaural" seems to have been adopted as 
descriptively generic, and we have used the word in that sense as being descrip- 
tive of certain effects rather than of certain systems. The dictionary, while not 
particularly precise, seems to lean in the same direction (binaural having or 
relating to two ears; involving the use of both ears: Merriam Webster New 
International, 1936}. 

MR. MACNAIR: I wanted to point out that from the physical and engineering 
points of view there are more than one kind of system. We ought to admit from 
the outset that there are basically different kinds of systems, and therefore they 
should be referred to with different words. 

MR. OFFENHAUSER: Until the present time it has hardly been possible to 
classify such systems since a particular effect produced in any of the previous 
systems usually had as an inseparable accompaniment other effects, usually 
undesirable, which were not independently controllable by any suitable means. 

There still remains the problem of properly classifying the effects that we do 
consider desirable. It will require a consensus of opinion to determine suitable 
and proper classifications, and in order that that may be accomplished, there is 
required a study of the individual effects of themselves. One example is room 
echo, or effect, or reverberation. 

Let us suppose that this room is an acoustically simple room, without columns 
but with very hard, flat walls, and a hard flat ceiling. When a person talks in 
such a room, a listener gets one impression of the room's size. If we block off 
one-half of the room, as with a plaster block wall, the listener has another im- 
pression merely because the size and shape of the room have changed. 

We do not at the present time have technical terms to describe accurately the 
effects that we feel. Unless the effects are segregated, it would seem to me that 
we are going to have difficulty with any classifications that we may use in analysis. 

Let us again consider our acoustically simple room. We shall now modify it 
by using some absorption material uniformly over all the exposed surfaces. 
With listener and speaker in the same places as in the "hard" room, the effects 
will be different. The effect produced when the speaker is walking about in the 
"hard" room is certainly different from the effect produced when he is walking 
about in the treated room. 

If the room is then further modified so that it becomes a room such as this is 
acoustically, with its columns and its windows and its partially treated surfaces, 
the effect produced when the speaker walks about in such a room is certainly 
different from any of the other conditions described. 

MR. GOLDSMITH: Yes, you have mobility of the speaker and you have 
sonority of the surroundings, and you mix the sonority of the surroundings and 
the mobility of the sound source and get a wide variety of acoustic effects. 

MR. OFFENHAUSER: With this arrangement, it is possible to simulate many 
of these effects in reproduction when the sound-source or sources actually remain 

Feb., 1939] BlNAURAL RECORDING 153 

stationary with respect to the microphone. It is even possible to take a small 
orchestra, set up compactly for ordinary pick up and, by the manipulation of 
our controls, cause the reproduced orchestra to appear to spread out over a large 
area of, let us say, 1000 square-feet, or to contract into the area in which such 
a group of musicians would ordinarily perform. In addition to mobility and 
sonority we also seem to have a characteristic of the apparent source itself which 
we can call source size. This, too, is a variable. 

There is a decided advantage in this particular type of reverberation effect 
inasmuch as it is synthetic and is not dependent upon the limitations of physical 

MR. CRABTREE: It was my feeling that you kept switching from one speaker 
to the other. Would not the test have been better if you had covered up the 
loud speakers? 

MR. OFFENHAUSER: That is a good point. We had considered darkening the 
room and projecting a picture or some kind of visual color pattern but decided 
against doing so in order that we might demonstrate the system to you under 
the worst possible psychological conditions. If we obtain results under these 
conditions, we can consider this an acid test. 

MR. GRIFFIN : Is the particular type of speaker that you are using of necessity 
a part of the system? 

MR. OFFENHAUSER: Definitely not. We have used flat baffle speakers, 
directional horn speakers, and all sorts of other speakers, and can, to a varying 
degree, produce the effects with commercial speakers. Loud speakers with good 
high-frequency response are preferable, however. 

MR. ENGL: As I understand it, there are two separate electrical channels 
connected to the two loud speakers. It might be an interesting experiment to 
connect both channels to one loud speaker instead of two loud speakers. As 
far as phase-differences are concerned the result on the audience should be ex- 
pected to be the same. 

MR. OFFENHAUSER: If they were connected to the same loud speaker mecha- 
nism, you would get an effect similar to mixing. 

MR. ENGL: I mean to use the same mixing system. 

MR. OFFENHAUSER: It is impracticable to try it now. 

MR. KELLOGG: I should like to second Mr. MacNair's remarks and make 
a plea for reserving the term "binaural" for a really completely separated channel 
between two microphones. I believe the use of that term in patents is not as 
good a criterion as to what is the best usage of language as the scientific writings, 
because those who write patents may have excellent ideas and a good deal of 
ingenuity, but as a class they are not as careful probably as those who come 
along afterward and reduce things to careful analysis and classification. I 
believe that "binaural" is usually used by scientific writers in the sense of sepa- 
rated channels. 

MR. OFFENHAUSER: We have substantially separated output channels here, 
but our input, as we have described, is a single channel. 

MR. KELLOGG: Still it is not a binaural channel in the sense I have just 

MR. OFFENHAUSER: That is correct; we call it quasi-binaural. We would 
like to call your attention to the fact, however, that this system is by no means 

154 W. H. OFFENHAUSER, JR., AND J. J. ISRAEL [j. s. M. p. E. 

limited to monaural input and may be used with even better results with binaural 
microphone input. What we have demonstrated is the quasi-binaural system. 

MR. KELLOGG: That may be all right. It may be of interest to you that a 
number of years ago I witnessed a number of tests at our laboratories in Camden, 
in which we resorted to changes in phase and changes in intensity to shift sound 
apparently from one source to another, and it appeared that either an advance 
in phase or an increase in intensity would serve to shift the sound from one source 
to another. Within moderate limits, phase has preference, for if the intensity is 
pretty close, the one from which the sound reaches you first is what you consider 
to be the real source. However, with further increase in the difference in level, 
you presently reach a point where the louder one seems to be the source. This 
is when it almost completely subdues the other. Apparently our ears judge, so 
far as possible, by where the first impulse of sound comes from. 

MR. DAVEE: There are one or two points in this system that we should not 
overlook. The first was mentioned by Mr. Offenhauser and I would like to 
emphasize it : the possibility of moving the sound outside the limits of the loud 

Second, if each of you should walk about the room as we did last night, you 
would realize the rather complete coverage of the effect in this auditorium. If 
you have ever worked with binaural systems before, you know that the effect 
is usually quite disappointing when you get very far from the loud speakers. 
With this system, from my observation in walking about the room, the effect is 
very startling. One can walk about the room to his heart's content and the 
binaural effect is still there. The word "binaural" appears to me to be an ad- 
jective describing an effect rather than the name of a system. 

MR. WOLF: This system is definitely not a binaural system in the way we 
are accustomed to thinking of it. With regard to the phase relations, I thought 
it was an accepted fact that they did not make any difference in the acoustic or 
subjective effect. 

MR. ENGL: Perhaps I should not have used the term phase-difference, but 
rather time-difference. In other words, the effect here in question probably 
depends upon time differences. My idea was that similar effects could be pro- 
duced with one loud speaker because you can, of course, get two sound waves 
from one loud speaker with the desired time-difference between them. With 
regard to the expression "binaural," I think one might propose the term "stereo- 

MR. GOLDSMITH: In connection with phase delay, what is generally under- 
stood is that if the various frequency components of a given sound are altered in 
phase, the effect is not noticeably detectable. But if you have two complete 
replicas of a given sound, with all the components shifted bodily, a new effect 
of an echo occurs. 

MR. MITCHELL: What is the effect of the reverberation of the auditorium, 
comparing a live room with a comparatively dead room with the present 

MR. OFFENHAUSER: With this type of system, we can go into a room where 
reproduction is practically impossible with commercial conventional equipment 
and where even direct speech from a live speaker is unsatisfactory, and obtain 
improved intelligibility ; even better in certain cases than the live speaker himself. 

Feb., 1939] BlNAURAL RECORDING 155 

There is one other effect we have found that seems to be important and we are 
going to investigate it much further than we have so far. In the application to 
public address systems, we were able to adjust our apparatus in such a manner 
that we could increase the sound level in an auditorium at the feedback point 
by some 6 or 8 db. At the present time we attribute it to a form of negative 
reaction effect between the sound projected by the loud speakers and that picked 
up by the microphone or microphones. 

MR. GOLDSMITH: That is probably acoustic degeneration between loud 
speakers and microphones. 

MR. OFFENHAUSER: Quite likely. 



Summary. In past practice, acoustics has been overlooked as a function of the 
architectural planning of motion picture theater structures. The need for and the 
extensive use of sound-absorbing devices in existing buildings have led to reliance 
upon corrective methods in the planning of new designs. 

The constructive approach to the solution of acoustical problems in new design is 
achieved only through proper determination of the basic proportions, cubic-foot 
volume per seat, and detailed form of the auditorium structure. 

The purpose of this paper is to show that acoustics can be coordinated construc- 
tively with the other primary functions of theater planning to develop a more efficient 
and more economical design and one that truly expresses modern and creative archi- 

A critical distinction of modern architecture from prior technic 
lies in a more candid evaluation of function. Because of the persis- 
tence of superficial ornamentation, however, this fundamental is fre- 
quently lost in our conception of what really constitutes modern 
design. We need not here go into the history of the modern approach 
to architectonics ; suffice it to point out that it assuredly did not have 
its real origin in ornamentation. Instead, it began as a method of 
using our standard and new materials for the creation of buildings 
better suited to our need of them. 

Despite widespread digressions, which continue to exalt the purely 
aesthetic evaluations, modernism in architecture is the offspring of 
science, not of fine art. Modern science has revised our approach to 
most things. Giving us knowledge of a thousand venerable mysteries, 
it has discouraged circumlocution and falsity in our expressions gen- 
erally. To be really modern in- architecture is to go straight to the purpose 
of a building, and to develop it in plan and structure according to an honest 
acceptance of that purpose, providing in the forms and devices that 
serve it a beauty that is inherent. 

* Presented at the 1938 Fall Meeting at Detroit, Mich.; received December 
12, 1938. 

** Electrical Research Products, Inc., New York, N. Y. 
t Theater Architect, New York, N. Y. 



When the ideal of functional efficiency and proper aesthetic quality 
becomes our guide in designing a motion picture theater, the precepts 
of sound, light, and vision supply the basis for fundamental planning. 
Fortunately, the insistence upon such a basis has lost much of its 
radicalism, for which thanks are in a great measure due this Society. 
Through the efforts of the Projection Practice Committee 1 and of 
other groups and individuals, definite advances have been made in 
many engineering phases of theater planning. Correct vision, without 
obstruction, has been provided in a number of new designs, although 
much additional work is required in this field. Lighting in the audi- 
torium, coincidental with the picture presentation, is now being 
given more study. Other provisions for the patrons' comfort and 
enjoyment, such as air-conditioning, proper seating, and general 
arrangement and appointments are also receiving much more con- 
sideration. Unfortunately, however, practically no attention has 
been given in previous design practice to the relationship that exists 
between acoustics and the fundamental plan of the theater. This 
does not mean that the acoustical problem has received no attention. 
On the contrary, it has often received thoughtful treatment, but more 
specifically from what might be termed a corrective rather than a 
constructive point of view. In other words, the usual procedure has 
been first to plan the theater from all other aspects and, in many 
cases, even to go so far as to determine the decorative treatment of 
the interior, before considering acoustics. Then, as the final step (in 
cases where the subject of acoustics is given consideration in planning) 
sound-absorbing materials are selected with a view to correcting or 
compensating for acoustical deficiencies in the design definite as- 
surance being made first that these materials will fit a predetermined 
decorative scheme. 

This corrective approach to the solution of acoustical problems has 
become common practice because: (1) the preliminary basic form of 
auditoriums has not been planned for best acoustics; (2) the total 
volume of the auditorium structure has not been held down so as 
to fall within desirable limits, as it might have been in many new 
designs; and (3) the past tendency to follow tradition in architectural 
design practice has usually made it mandatory to utilize corrective 
methods. There is one other reason that should not be overlooked. At 
the time speech and music were added to films, sound-absorbing de- 
vices were required for many existing structures having poor acousti- 
cal conditions. Perhaps from force of habit, reliance upon these de- 


vices has extended into the planning of new theaters. As a result, 
basic acoustical design has been overlooked as one of the sources of 
effective architecture. 

It is not the purpose of this paper to discourage the use of acoustical 
materials for the treatment of motion picture theaters. Such ma- 
terials may be required for the following special cases: namely, for 
new theaters having very large seating capacities ; for existing theaters 
having fixed forms that produce objectionable sound reflections ; and 
for both new and existing structures having excessive cubic-foot 
volumes per seat. 

It is proposed to show, however, that more efficient and more 
economical theater structures can be built when basic acoustical re- 
quirements are coordinated with the other primary functions of 
theater planning. There are four outstanding reasons why this con- 
structive approach will produce more successful results: (1) today 
the various elements affecting the control of sound in a design can be 
studied initially and planned correctly, with the result that very little 
or no acoustical material need be provided for the wall or ceiling sur- 
faces; (2) minimum surface treatment makes for better acoustics, 
because (a) the proper character of reverberation and absorption can 
be assured, and (b) less critical conditions need finally be met in 
balancing the frequency absorption characteristic of the theater; (3) 
in cases where little or no acoustical material is required, the architect 
is at liberty to use ordinary, every-day materials, thereby making for 
greater flexibility in design; and (4) when a theater is efficiently 
planned in this way, substantial economies can be realized not only in 
acoustical treatment but also in other phases of theater planning. 

From the architectural standpoint, planning for proper acoustical 
conditions in the initial design stage does not preclude the ability 
to obtain pleasing forms or surface finishes for the auditorium. Ac- 
tually, creative design is more readily inspired by this approach. 


Two fundamental factors that must be considered as the first step 
in the functional acoustic planning of a motion picture theater are: 
(1) the preliminary outline or basic form of the auditorium, establish- 
ing its proportions of length, width, and height; and (2) the volume 
or cubical content of the auditorium structure in its relationship 
to the seating capacity. 


Actual design practice indicates that the most efficient control of 
sound reflections and the best distribution of sound energy can 
usually be obtained in theater auditoriums where the ratios of 
width to length fall within the limits of 1 : 1.4 and 1 : 2. 2 When the 
the length becomes greater than twice the width, difficulties arise from 
a multiplicity of sound reflections occurring between the side wall 
surfaces. When the ratio of width to length is less than 1 : 1.4, the re- 
sulting design becomes an unfavorable one from the standpoints of 
proper sound distribution and vision. Furthermore, this design 
creates an unusally large rear wall, which is often a source of objec- 
tionable sound reflections. 

The limits of ratios recommended above for the floor plan are not 
meant to suggest that a strictly rectangular outline must be adopted 
for the fundamental design. These ratios also apply to the average 
dimensions for the width and length of an irregular basic outline, 
such as one having a moderate splay in the preliminary form of the 
side walls or a generally nonsymmetrical arrangement of outline 

Establishing the ceiling height in its most practicable and best 
acoustical relationship to the horizontal dimensions is the next 
element to be considered in fundamental planning. Ceiling height is 
very important because it affects both the proportions and the 
structural volume of the auditorium. 

From an architectural viewpoint, the determination of ceiling 
height is governed by three factors, namely: (1) sight-line require- 
ments; (2) width of the light-beam and its projection angle to the 
screen; and (3) the general appearance of the auditorium. 

From the acoustical standpoint, two other important factors should 
be included in the determination of ceiling height. These are: (1) 
the proper relationship of the ceiling height dimensions to the hori- 
zontal proportions; and (2) the optimum cubic-foot volume per seat 
required for a given design. 

A ceiling-height ratio can not be fixed that will be adaptable to all de- 
signs. The best ratio can be established only by a study of the hori- 
zontal dimensions and by a preliminary analysis of the cubic-foot vol- 
ume requirements for the initial control of reverberation time in a 
given design. 

Excessive ceiling heights are commonly found today in auditorium 
design practice. The large structural volume per seat and the pro- 
longed reverberation time resulting from this acoustical defect in 


theater planning have produced a need for corrective materials in 
many new designs. 

The following study will show the variations in basic proportions 
and structural volume introduced in the planning of a theater audi- 
torium seating 900 persons. This study will also show the reasons 
for these variations and how they can be minimized. 

From an acoustical standpoint, the structural volume of an audi- 
torium seating 900 persons should lie between 120 and 130 cubic- 
feet per seat. The factors affecting the determination of these limits 
are: (1) the optimum or best times of reverberation at different fre- 
quencies for reproduced sound, 3 and (2) the fixed and variable sound- 
absorption required to produce these times of reverberation. 

Fixed absorption means the absorption provided by theater chairs, 
carpets, and interior surfaces of standard furred construction, finished 
in an ordinary manner. Variable absorption is the absorption nor- 
mally provided by the audience. "Optimum" reverberation times are 
usually based on an audience condition approximating two-thirds of 
the house seating capacity. 

The chairs constitute the major part of the fixed absorption for a 
theater initially planned to be acoustically functional in design. To 
ensure that the variable absorption, that is, the audience, will not 
effect a major change in the reverberation time, it is very important 
that these chairs be of an efficient upholstered type. The type com- 
monly used for theater seating today is one having a leather-covered 
spring bottom and a fully padded mohair or tapestry-covered back. 
In the standard 20-inch width this chair has a sound absorption value 
equivalent to more than two-thirds that of the average person. The 
use of such a chair has been assumed for the following study. 


From the standpoint of vision the proportions and cubic-foot vol- 
umes of auditoriums vary for three different reasons. These are : 

(1} The type of seating arrangement used in the horizontal dimension of the 
auditorium determined by the number of seats and aisles to be arranged across 
the width of the auditorium. Types in common use are (a) 14 seats with a wall 
aisle on either side of the seating area; (6) 2 aisles separating three banks of 
seats, the middle bank being 14 seats wide and the side banks against the walls 
being 7 seats wide; (c) 2 banks of 14 seats each separated by a single aisle having, 
in addition, 2 wall aisles; and (d} three banks of 14 seats, each separated by two 
aisles having, in addition, two wall aisles. 

Feb., 1939] 



(2) The type of seating arrangement employed in the vertical dimension of 
the auditorium, such as (a) all seats on a single level; (&) a single general level 
of seats with the rear portion of the seating area somewhat elevated, with a 
cross-over separating the raised portion from the remainder, this type being 
commonly called a stadium design; (c) a modified stadium design in which the 
raised portion of seats in the rear is placed high enough so as to cover the cross- 
over mentioned in the b type; and (d) use of upper seating levels partially over- 
hanging the seating area of the level below. 4 

(5) The inclination or inclinations of the floor for the main or orchestra level, 
such as (a) a steep downward inclination toward the screen; (6) a modified 
downward inclination toward the screen; (c) a modified downward and then up- 
ward inclination toward the screen; and (d) only a slight downward and then 
upward inclination toward the screen. 


VOLUME 136* e*,, t PI* SIM 


120i cu r, fft SEAT 

FIG. 1. Longitudinal sections for five values of cu.-ft. volumes per seat. 

The degree of inclination of the floor in all cases is affected by the 
manner in which the seats are placed behind each other. When these 
seats are arranged in staggered fashion so that the center of any seat 
is always directly behind the dividing armblock of the preceding 
seat, the inclination of the floor may be reduced by almost one-half. 
Variations in floor inclination directly affect the height and inclina- 
tion of the upper seating levels and the placing of the projection 
room, thereby the total height of the auditorium. 



The study presented in Fig. 1 has been made to investigate which 
of the various possible auditorium designs would prove most efficient 
from both the visual and auditory standpoints, keeping in mind that 
economy in construction and architectural appearance are also im- 
portant guiding factors. An auditorium seating 900 persons was 
selected for this study because this capacity has been found to answer 
the needs of the average motion picture theater and because a large 
proportion of the theaters now being erected approximate this 
capacity. 5 

It is interesting to note in the five theater designs shown that the 
structural volumes of the auditoriums vary from 108,450 to 134,100 
cu.-ft. Furthermore, the required screen width varies from a mini- 
mum of lQ l /z ft. to a maximum of 22 ft. due to the increases in maxi- 
mum viewing distance. Such variations in design are not justified 
when the seating capacity is the same in all cases, as it is in all the 
designs here shown. 


Cu.-Ft. of Max. Viewing 

Design Vol. per Seat Distance Screen Width 

A 151 104ft. 20ft. 

B 148 119 22 

C 130 105 20 

D 136V2 89 16 6 in. 

120 1 /* 89 16 6 

Ceiling heights have been kept down to a minimum in all five de- 
signs, and the seating arrangement in the horizontal dimension is the 
same in all cases, using the type having two aisles separating three 
banks of seats, the middle bank being fourteen seats wide and the 
side banks against the walls being seven seats wide. This arrange- 
ment in the horizontal dimension was selected for these studies be- 
cause it is the most efficient plan for capacities of approximately 900 
seats, requiring the least amount of aisle space and thereby effec- 
tively reducing the total volume for all the design studies. 

Table I shows the resulting characteristics of the five designs shown 
in Fig. 1. 

In the design types A, B, and D shown in Fig. 1, the slope of the 
orchestra floor is approximately what has been commonly used in 
past practice. This slope ordinarily does not afford a sufficiently 
unobstructed vision of the screen. To correct this defect, an increase 

Feb., 1939] 



in the slope in these types would result in a slight increase in the total 
volume where the volume is already excessive. However, visibility 
could also be improved in these designs by the use of a stagger system 
of seating which would effect a slight reduction in the total volume. 
This reduction would benefit design D only. Designs A and B would 
still provide excessive volume. 

In designs C and E the staggered system of seating has been used 
for the lower seating areas. However, a non-staggered plan could also 
be used which would result in a floor that would pitch downward 
toward the screen approximately one foot more and pitch upward 
toward the screen in the front half of the floor to a point about level 
with the floor behind the seats farthest from the screen. The volume 


/ ^ 




45 cu 

:E VA 































O 1 








O M 




FIG. 2. Volume of 100 theaters seating 800-1000 persons. 

added to designs C and E due to using a non-staggered plan would 
raise the total volume only a negligible amount. 

The designs shown here have horizontal shape ratios varying from 
1 : 1.65 in designs D and E to 1 : 2 in design B. Although all these 
horizontal ratios come within the acoustical limits heretofore recom- 
mended, it is particularly significant from the analyses that the proper 
vertical solution of a design not only results in good basic form but in 
most cases is the primary factor determining the efficient control of 
structural volume. 

The data given in Fig. 2 provide an interesting parallel to this study 
and show the variations in volume per seat for one hundred theaters 
built recently, seating between 800 and 1000 persons. Seventy-one 
of this number are theaters of the balcony type, whereas only twenty- 


nine are single-floor houses. It is important to note that the peak of 
this curve for volume per seat vs. the number of cases lies between 
140 and 160 cu.-ft., and that the net average value for the 100 cases 
is 145 cu.-ft. per seat. These data suggest that the greater percentage 
of present-day theater structures have excessive volumes per seat. 
This fact is in turn a direct indication of the lack of thought given to 
coordinating the auditory and visual requirements in fundamental 
planning, particularly since in the majority of these cases excessive 
volume was a result of excessive ceiling height. 

The advantages to be gained from providing lower ceiling heights 
than have heretofore been found in general practice are: (1) a lower 
initial time of reverberation, resulting from a smaller volume per 
seat, (2) reduced surface areas to be treated acoustically, permitting 
more efficient control of sound by shaping the interior surfaces, and 
(3) economies realized in construction costs through the elimination, 
or reduction in quantity, of acoustic materials usually required, as 
well as through the use of smaller quantities of ordinary building 

Two additional advantages result from the proper control of ceiling 
height and structural volume that should not be overlooked. One is 
that economies in the size and capacity of sound-reproducing systems 
are frequently made possible in theater auditoriums having reduced 
volumes per seat. The other advantage is that excessive power output 
is not required to compensate for high energy losses frequently caused 
by the use of acoustic materials on wall or ceiling surfaces. 


The final phase of theater planning influencing both the acoustical 
condition and the architectural treatment is the detailed shaping or 
styling of the surfaces within the auditorium. This phase of planning 
is also very important because it functions with the proper determina- 
tion of basic outline and structural volume to control the character 
of sound and the destination of sound reflections. 

When an auditorium is to be used principally for direct speech or 
musical presentations it is desirable to plan and arrange the interior 
surfaces so as to aid in reinforcing the sound produced on the stage. 
In the motion picture theater, however, where sound is reproduced 
and adequate power can be provided electrically, the acoustical 
problem is not one of designing surfaces to gain reinforcement. 
Rather, the interior surfaces of this auditorium should be shaped and 

Feb., 1939] 



arranged so that they function to break up or disperse sound energy. 
This result can be accomplished most successfully in cases where 
favorable basic proportions are maintained and where the initial time 
of reverberation is efficiently controlled by the structural volume of 
the auditorium. 

Irregularity of surfaces arranged to break up or disperse sound 
energy may take the form of angular or sloping sections, nonsym- 
metrical broken offsets, or convex projections. The size of each sur- 
face unit, its position and arrangement on a wall or ceiling, and its 



FIG. 3. Theater form showing angular surfaces for controlling sound reflection. 

degree of projection from a horizontal or vertical line will depend 
upon the requirements for control of the destination and dispersion 
of sound reflections in the individual design. The surface of a major 
angular or convex projection may in turn be broken into smaller in- 
crements if required in special cases for dispersion of the very high 


Fig. 3 shows the longitudinal and cross-sectional views of a motion 
picture theater planned to seat 900 persons. This theater was 
recently designed in accordance with the principles outlined in this 


paper and is now under construction. The horizontal proportions 
of the auditorium are in the ratio of 1 : 1.79 and the structural volume 
is 123 cu.-ft. per seat. No sound-absorbing materials are used on 
either the wall or ceiling surfaces of this auditorium. 

These surfaces are of furred construction and are finished in ordi- 
nary hard plaster. The side walls are composed of a series of horizontal 
angular or sloping sections which vary not only in width but also in 
their degree of projection from a vertical line. The rear wall area 
exposed to the incidence of sound is reduced to a minimum and a 
convex projection is incorporated in the design of the balcony rear 
wall. The ceiling surface, which takes the form of sloping planes 
joined by convex sections, is also designed, as are the wall surfaces, 
to control the destination and dispersion of sound reflections. 


The authors have attempted to show in this paper that through the 
proper coordination of auditory, visual, and esthetic requirements, 
it is possible to plan more efficient and more economical theater 
structures than have in most cases been designed in the past. 

In viewing the various outline forms presented in the foregoing 
study of typical designs, much is to be said in favor of plans having 
an upper level of seating. Such a plan usually offers the most 
efficient solution to the control of horizontal proportions, ceiling 
height, and volume per seat, assuming that the requirements for 
correct vision are properly incorporated in fundamental planning. 
This form of design also introduces a structural break-up at the 
rear of the auditorium that is initially helpful in controlling sound 

The planning of detailed acoustical forms for the wall and ceiling 
surfaces offers unusual possibilities for the creation of new modes or 
styles in the esthetic treatment of the theater auditorium. 6 ' 7 Un- 
questionably, many highly interesting and altogether unique designs 
will develop in future planning when the functions of the motion 
picture theater are in reality adopted as the inspiration for creative 
and efficient architecture. 


1 Report of the Projection Practice Committee, /. Soc. Mot. Pict. Eng., XXX 
(June, 1938), p. 636. 

2 POTWIN, C. C.: "Theater Acoustics," Architectural Record (Building Types 
Section) (July, 1938), p. 119. 


3 POTWIN, C. C.: "Theater Acoustics Today, "Better Theaters (Aug., 1937), 
p. 36. 

4 SCHLANGER, B.: "Motion Picture Theater Shape and Effective Visual 
Reception," J. Soc. Mot. Pict. Eng., XXVI (Feb., 1936), p. 128. 

5 SCHLANGER, B.: "Cinemas," Architectural Record (Building Types Section), 
(July, 1938), p. 113. 

6 "Acoustical Forms as Decoration," Architectural Rev. (London), LXXXIII 
(April, 1938), p. 207. 

7 BAGENAL, H., AND WOOD, A.: "Planning for Good Acoustics," E. P. Dutton 
fir Co. (New York, N. Y.). ( Vide Chapt. 3, Sec. 15, p. 82.) 


MR. CRABTREE: This has been an ideal demonstration of a collaboration 
paper, and likewise, a demonstration of collaboration in presentation. I have 
long had in mind the idea that the Society should make definite recommenda- 
tions for architects in regard to (1} architectural, (2) acoustical, and (3) optical 
features of motion picture theaters. It would seem to be in order to suggest 
that our President appoint a Theater Construction Committee, which could 
draw up definite recommendations. We already have the assurance of the 
architectural societies that after such recommendations have been fully discussed 
by our own organization they would then publish them and discuss them in 
their organizations, after which modifications could be made and the recom- 
mendations finally drawn up and circulated. 

Where is this theater being constructed? If I am in that vicinity I will 
certainly make a point of going to see it. 

MR. SCHLANGER: At Hamden, Conn. 

MR. CRABTREE : Are there any in the vicinity of New York City that in any 
way approach or simulate this one? 

MR. SCHLANGER: A theater recently completed in New York and similar in 
appearance to the small theater on the French Liner Normandie has a minimum 
auditorium height and a floor shape designed in accordance with the latest 

MR. POTWIN: In duplicating the architectural treatment of the original 
Normandie theater, the limitations placed on form made the acoustical design 
somewhat less flexible than the Hamden project. Nevertheless, it was possible 
to establish a favorable relationship between the structural volume and total 
seating of the auditorium and to shape and arrange wall and ceiling splays to 
promote the efficient control of sound reflections. On this basis a minimum 
amount of acoustical material was used, this material being confined to a very 
limited portion of the rear wall area. 

MR. CRABTREE : In some theaters it is the practice to have intermissions and 
throw on the lights so one can see the beauty of the decorations; when the show 
is over they put on the lights again. In this style of theater it would seem almost 
imperative that the lights never be thrown on, unless a decorative system of 
color or spotlighting is provided. In other words, there is no question that if 
the white lights are thrown on, such a theater will appear somewhat like a barn. 

MR. SCHLANGER: The simple architectural forms proposed would lend them- 
selves effectively to color lighting. 


MR. GREENE : Would it not be possible to use a very simple projected design 
upon the side walls between pictures, particularly if you are not going to raise 
the level of illumination high? 

MR. SCHLANGER: That is an excellent idea and has been done successfully. 
Certain types of cut outs can be made and placed in front of the light-sources. 
Variations in the images would make it possible to create more designs per year 
than could be achieved with any fixed forms of decoration. It can be done 
from the fascia of the mezzanine, from the projection room, or from hidden spots. 

MR. CRABTREE: Perhaps kaleidoscopic changes could be used. 

MR. SCHLANGER: Yes, that has been thought of. 

MR. CRABTREE : With regard to the aisle seats, when the seats are staggered, 
why is not the end seat in every alternate row made a little wider so the edges 
of the aisles will be straight? 

MR. SCHLANGER: If the seats are staggered there is a 10-inch difference be- 
tween the seat and the aisle line. 

MR. CRABTREE: Why not make the end seat about ten inches wider? 

MR. SCHLANGER: It would be out of proportion. However, we could com- 
promise by making the seat three or four inches wider, so that the indentation 
would not be so obvious and the width of its arm block could also be increased. 

MR. CRABTREE: Some theaters furnish seats for the hard-of -hearing. Why 
not reserve those seats for the corpulent? 

MR. SCHLANGER: No doubt those seats would be more comfortable for the 
extremely corpulent persons. 

MR. CRABTREE: Do you think, Mr. Schlanger, that the data are sufficiently 
far along that the Society would be in position to make definite recommendations 
if we had a committee as suggested? 

MR. SCHLANGER: The committee could be formed, but it would have to work 
in close collaboration with the Projection Practice Committee and the Sound 

MR. CRABTREE: The committees have been assembling data for some time 
past. Do we have enough data now, or do we have to do more experimental 

MR. SCHLANGER: Naturally, more research work is always in order. How- 
ever, the new committee could compile its own data and report to the other 
committees as to what additional data are required from them in order to arrive 
at the proper conclusions. 

MR. POTWIN: Unquestionably with the data now available it should be 
possible to arrive at definite standards for a number of phases of theater design 
and construction. 

MR. CRABTREE: If the committee did nothing more than prevent the archi- 
tects from placing lights right under one's nose, I think the effort would be well 
worth while. 



Summary. An analysis of sound-picture reproducing-system characteristics, in- 
cluding electrical and acoustical response data collected in the interest of determining 
the possibilities involved in obtaining an average characteristic for reproducing vari- 
ous film products with uniform response over several combinations of loud speaker 
equipment. With the aid of a curve tracer having a long-persistent cathode-ray 
screen, a photographic record was made of the characteristics, starting with various 
forms and amounts of equalization and exploring their relationship to the power- 
handling capacity of amplifiers. Following through the system, this record shows the 
characteristics of dividing networks under various conditions of load, and finally the 
acoustical response curves taken for comparison of the loud speaker equipments under 

The measurements of loud speaker combinations included various types of units, 
both permanent-magnet and energized, low-frequency horns ranging from open back 
baffles to folded horns with specially designed rear-loading compartmsnt, and high- 
' frequency multicellular horns of various configurations and constructional details. 

After establishing the natural characteristics of the various equipments involved, 
careful listening tests were made over an extended period with samples of commercial 
prints and other recordings. A description follows of the difficulties and problems 
involved in an effort to obtain one overall chiracteristic, which would give satisfactory 
reproduction for all types of material. The final results are shown, with a short dis- 
cussion of the methods for duplication in other equipment combinations, and con~ 
elude with recommendations for future designs and ratings. 

Our interpretation of the goal of all organizations concerned with 
sound in the motion picture industry is to produce in every theater 
throughout the world the sounds considered desirable by the director 
or whoever is responsible for the production. In order to achieve 
this goal, it is obvious that the performance of the equipment must be 
so well understood, and so well standardized, that the director in 
his review room can hear his product as his customers will hear it. 

It would be very convenient if we could standardize the perform- 
ance of theater equipment by specifying that it should have a flat 

*Presented at the 1938 Fall Meeting at Detroit, Mich.; received November 
18, 1938. 

* International Projector Corp., New York, N. Y. 




[J. S. M. p. E. 




gain-frequency characteristic ; that it should introduce no non-linear 
distortion at any and all levels; and that the distribution should be 
uniform to every seat in the theater. To adhere even approximately 
to such a standard would, however, work a hardship on both the 
theater owner and the producer. It would make the theater owner 
pay more than is necessary or desirable for him to pay for his equip- 
ment, and the best product that the producer could turn out would 
suffer in signal-to-noise ratio and the general acceptability of the 

By using film as a recording method, we accept a medium in which 
most of the annoyance from noise is concentrated in the high-fre- 
quency end of the spectrum. Most of the unpleasant distortion 
experienced in film reproduction also occurs at the same end of the 
frequency characteristic. Overall performance can, therefore, be 
improved by utilizing a reproducing system characteristic in which 
the response falls off at the high frequencies. If the producer is to 
use noise-reduction of the type most generally available, the low- 
frequency response of the reproducing system should be limited so 
that the listener will not be annoyed by hearing the operation of the 
noise-reduction device. With this objective in mind, it appears that 
the reproducing system characteristic should be standardized in such 
a way as to derive the maximum benefit in signal-to-noise ratio and in 
the reduction of undesirable distortion, considering at the same time 
the theater owner's interest in reduced cost of equipment. The 
Research Council of the Academy of Motion Picture Arts and 
Sciences, through the work of its Committee on Standardization, has 
established a basis for the desired attainment. It has brought out 
the desirability of certain characteristics that must be carefully con- 
sidered from every angle. In certain instances, some of these charac- 
teristics might be misinterpreted unless proper consideration is 
given to the variable factors involved. 

In Fig. 1 an effort has been made to indicate diagrammatically the 
various steps of the overall recording and reproducing process. It 
will be noted that variations exist throughout the entire chain. In 
the recording, consideration must be given to the acoustics of every 
set. Microphone placement has not only been a point of con- 
troversy, but has always been a factor of adjustment in the overall 
characteristic. The technic of mixing is another vital point which is 
entirely an adjustable feature. Determination of the proper amount 
of equalization and the general amplifier characteristics are additional 



[j. s. M. p. E. 


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* MOTf:- OfFfaeNCf, F. t. HOtPfff: 'flftr&CAl ttfriVOaKS FOP SOUNO BfCO0DING, ' J S M P.f. /I/Of. 1936 

Fic f 2. Flexibility and limitations in recording and reproducing. 


tools by which the recording personnel may adjust the final film 
characteristic to afford the most pleasing and dramatic reproduction 
in the theater. 

In the laboratory is found a situation that contributes further to 
the variations in film characteristics. It is understood that for 
extreme conditions high-frequency losses may range from to 8 db. 
at 8000 cycles. While a considerable proportion of this may be 
anticipated in the adjustment of recording characteristics, the power 
ratios for unanticipated variations are important, as they occur in 
the high-frequency range. Minimizing printer slippage is a very 
pertinent factor in any attempt to obtain clean and smooth high-end 
reproduction free from harshness. 

The principal variables in reproducing systems may be grouped 
under the headings of flutter, electrical characteristics, loud speaker 
characteristics, and theater acoustical conditions. While the 
electrical characteristics have heretofore been established as extend- 
ing from film input, including the optical system, to a resistance 
termination at the output of the amplifier, it is proposed to show 
here the inadequacy of such standards. Even measurements to voice- 
coil terminations are not a true indication of the influence of the horn 
equipment and the acoustical coupling on the aural response that is 
sold to our customers. 

In our interest of standardization in the theater, extensive tests 
were made with various types of reproducing equipment. If systems 
generally are manufactured to conform to specified requirements, it 
must follow that similar results should be expected in the same 
acoustical environments. The differences actually encountered, and 
the reasons therefor, were indicative of the present necessity for most 
careful consideration of the entire program of standardization. 
While it was disturbing to note the large amount of variation existing 
in the characteristics of film products today, it is believed that the 
hope of remedying this situation lies in the establishment of specific 
end results to which recording, laboratory, and reproducing groups 
may work. 

Fig. 2 shows a tabulation of an outline wherein desirable elements 
of flexibility are maintained for recording, in direct contrast to the 
present imposed limitations in the reproducing group. 1 In order 
to establish a coordinated program for overall betterment, each 
group must assume its rightful share of responsibility, and be per- 
mitted complete control over matters within its own jurisdiction. 



[J. S. M. P. E. 

In the laboratory, it is suggested that further studies be made, par- 
ticularly in the interest of reducing the ill effects of printer slippage 
and of maintaining closer control of high-frequency losses. In the 
theater field, it is desirable, in the interest of our customers, to be 

S 30 fOO 300 fKc fOKC 


FIG. 3. Overall acoustic characteristic. (Adjusted for 
most pleasing response.) 

allowed freedom from component or sectionalized specifications. 
End results, not details, are the logical basis for performance 

As a general arrangement, our own tests indicated that a flat 
overall acoustic characteristic was not always the best. Fig. 3 

\ \ + 
5 * o o, 
















tOO 300 /AC 


FIG. 4. Overall acoustic characteristic. (Showing acous- 
tic and electrical modifications.) 

shows the acoustic characteristic found to be most desirable in this 
particular theater. 

When comparison was made with similar curves, obtained from a 
number of widely scattered theaters wherein the quality of reproduc- 
tion has been approved by various technical groups, it was noted that 


a flat overall acoustic response did not qualify as giving the most 
pleasing reproduction. It was observed in general that the level 
in the region of 250 cycles was approximately 6 db. lower than the 
balance of the characteristics. 

Upon analysis it was found that such a characteristic as shown in 
Fig. 2 creates an impression of roundness or fullness of the bass notes 
without causing too much heaviness in the region where chest tones 
become objectionable. From this the natural deductions would 
point to insufficient dialog equalization in recording, but such con- 
clusions can not be established until the studio review room acoustic 
characteristics are known. Our analysis was made by direct A-B 
comparison with a system whose overall acoustical response was 
intentionally made flat through this region, as shown in Fig. 4. 
This figure shows also the effect of acoustic and electrical networks 
that may be used to alter the characteristic. In passing, it may be 
pointed out that the electrical network offers considerable advantage 
in that it can be made adjustable at very low cost. 

It is interesting to observe how this "sway-back" characteristic 
has been obtained by using component parts which in themselves all 
have straight lines in the "sway-back" region. A study of these 
conditions was made, using the RCA curve tracer 2 provided through 
the courtesy of Mr. L. C. Hollands of the Radiotron Division of RCA 
in Harrison, N. J. Figs. 5, 6, and 7 show the measured acoustical 
characteristic of a system wherein the straight-line elements were 
connected together, each in a different manner. In each case a 
dividing network, 3 designed to operate between equal impedances, 
was used, and the high-frequency branch terminated by a load of the 
proper value. The measured electrical characteristics of this net- 
work have been plotted on each curve. 

In Fig. 5 the low-frequency units were arranged to provide a 
matched impedance termination. In Fig. 6 the low-frequency load 
was changed so that the impedance ratio between the network and the 
load was 12 to 6. In Fig. 7 the low-frequency units were arranged 
so that the impedance ratio was 12 to 1.5. These figures show the 
effect of impedance mis-matching of the network and the loud 
speakers, and indicate the importance of impedance relationships 
and the definite necessity of providing standards that are more in- 
clusive than the present form of electrical characteristics which are 
measured across resistance terminations at the amplifier output. 
The same overall response can be obtained by redesigns of the net- 



[J. S. M. P. E. 

60 200 400 IKC 



FIG. 5. Overall acoustic characteristic. (Network 
output 12 ohms, l.-f. load 12 ohms.) 

o eo 200 400 me tone 


FIG. 6. Overall acoustic characteristic. (Network 
output 12 ohms, l.-f. load 6 ohms.) 

^oo 400 we 



FIG. 7- Overall acoustic characteristic. (Network 
output 12 ohms, l.-f. load 1.5 ohms.) 


work wherein the low-frequency branch is purposely made to have a 
higher impedance than the load into which it will work, or by reduc- 
ing the voice-coil impedance of the low-frequency units. 

In reviewing numerous acoustical response characteristics, varia- 
tions in the upper end of the frequency spectrum were noted. The 
degree of tolerance for highs, the acoustical condition of the theater, 
the efficiency and response characteristics of the horns and loud 
speaker units, the effect of printer slippage, flutter, transient distor- 
tion resulting from too sharp cut-off niters, resonance conditions, or 
phase displacements may all have been contributing factors. Our 
tests disclosed positive differences in the response characteristics of 
various types of horn equipment. 

A substantially flat system 4 is probably the most desirable type 
to use in the theater for reasons of economy of construction and 
simplification of general maintenance and tuning-up procedures. 
It is believed that specifications should not require complicated, 
costly, or critical designs in theater systems, particularly in view of 
the flexibility at present available in recording equipment. Further- 
more, the cost of modifying recording systems to insert therein any 
desired characteristics and so maintain a desirable response in the 
theater would appear to be more economical for the industry as a 
whole due to the relative number of equipments involved. 

Mention has previously been made of the necessity for maintain- 
ing the desired characteristic in the theater at any and all sound 
levels. It will be readily appreciated that this problem lies beyond 
the scope of this paper as it must include data on various types of 
amplifier design, involving triodes, beam power tubes, pentodes, with 
and without feed-back, and various types of feed-back circuits. 

With regard to the relationship between power output and fre- 
quency response, a composite picture (Fig. 8) was made to show how 
a given amplifier characteristic was altered when that amplifier was 
pushed to its maximum output. In this particular instance, both 
ends of the frequency spectrum were initially raised about 6 db. 
above the 1000-cycle level. It will be noted that as the output of 
this amplifier was increased, the characteristic approached a "ceiling" 
and finally flattened out. 

Fig. 9 shows the overdrive characteristic of the same amplifiei 
for various frequencies. It will be observed that in this particular 
case the various curves show very little departure from each other 
Overdrive characteristics of another amplifier are shown in Fig. 10. 



[J. S. M. P. E. 





rf 1? 








s s 

5 * 

^ x ^" 1 *-^ 



O $ 

K>0 300 IKC 


FIG. 8. Frequency response characteristic. (For various 
output levels.) 


Z 00 

O / 2 3 4 S 67 S 9 to ft Ig 13 


FIG. 9. Overdrive power-frequency character- 
istics. (Feed-back type.) Abscissas represent 
input increase in db. above rated load. 


<OO-l\)lM4tlxOi vi 















r ^- 











) i 2 j 4 s e 7 a 9 to ft tz a 


FIG. 10. Overdrive power-frequency charac- 
teristics. (Other types of theater amplifiers.) 
Abscissas represent input increase in db. above 
rated load. 


Here it will be noted that as the input level is increased the low- 
frequency power output will not increase beyond its compression 
point, but at the higher frequencies it will continue to deliver more 
and more power. Under conditions of extreme overdrive, it may be 
expected that the power delivered by such an amplifier to the high- 
frequency units may be two to three times the amount that can be 
delivered to the low-frequency units. With this situation it would 
be particularly difficult to maintain any predetermined character- 
istic in a theater at all levels. With demands for increased power 
output to be provided in order to obtain the proper dramatic effect 
for various types of recordings, the tendency to overdrive amplifiers 
will inevitably grow. It appears, therefore, that standards for elec- 
trical power must give these factors further consideration. 

With respect to power ratings and requirements, 5 attention is 
called to the block diagram of power amplifiers shown in Fig. 1. 
In the upper grouping, the amplifiers are paralleled ahead of the divid- 
ing network. The total wattage available would naturally be the 
algebraic sum of the individual amplifiers, and if no attenuation is 
provided in the dividing network both high- and low-frequency 
units will obtain that same total amount of power in their respective 
frequency ranges. In the lower group, where the dividing network is 
inserted ahead of the power amplifiers, it is common practice to use 
less power in the high-frequency branch by reason of the relative 
efficiencies of the high- and low-frequency loud speaker units. It 
has come to our attention that in discussions of power ratings for 
volume or seating requirements the total power in these two branches 
has been used, while in reality the maximum power does not exceed 
the amount that is diverted in the low-frequency branch alone. 
This illustration is made as further proof of the possibilities of mis- 
interpretation of standards, and at the same time to indicate addi- 
tional reasons for adopting acoustical standards throughout. 
Without a doubt the feeling exists that acoustical measurements 
e meaningless, and that adequate test equipment is not now 
ailable. Comparison of our own work with the results obtained 
y others prevent our subscription to this theory in its entirety 
Improvements can and always will be made, but our work in this 
field has led us to believe that the present facilities provide a far more 
accurate indication of comparative response characteristics than any 
electrical measurements, particularly those of the spot-frequency 



180 F. DURST AND E. J. SHORTT [j. s. M. p. E. 

In conclusion, it is evident that if our goal of standardized repro- 
duction is to be achieved, investigations should be continued con- 
cerning the overall characteristics of reproducing systems. It is 
firmly believed that to carry this out completely, and to avoid the 
pitfalls of misinterpreting component part specifications, overall 
acoustical performance characteristics must be the criteria, and final 
acceptance tests and tune-up procedure must be based upon the use 
of the warble film and acoustical measurements, rather than sec- 
tionalized response tests. It is believed, in this connection, that 
the manufacturer should be allowed to decide the methods by which 
he will provide this final characteristic. Basically, the problem 
resolves into determining the best overall acoustical characteristic 
to which film producers can most readily and consistently adjust 
their product, at the same time keeping the cost to exhibitors at a 
minimum. Last but not least, it is essential that the listening 
facilities of both patrons in the theaters and the producers in their 
review rooms be made equivalent in order that they may obtain the 
same reactions. 

Appreciation for his cooperation is expressed to Mr. J. B. Sherman 
of the RCA Radio tron Division, Harrison, N. J. 


1 HOPPER, F. L.: "Electrical Networks for Sound Recording," /. Soc. Mot. 
Pict. Eng., XXXI (Nov., 1938), p. 443. 

2 SHERMAN, J. B.: "An Audio-Frequency Curve Tracer," Proc. I.R.E., 26 
(June, 1938), No. 6, p. 700 

3 "Dividing Networks for Loud Speakers," Technical Bulletin (March 3, 1936), 
Academy of Motion Picture Arts & Sciences, Hollywood, Calif. (cf. Fig. d, p. 

4 "Standard Electrical Characteristics," Technical Bulletin (June 8, 1937), 
Academy of Motion Picture Arts & Sciences, Hollywood, Calif, (cf. p. 3). 

6 "Procedure for Projecting 'Hi-Range' Prints in the Theater," Technical 
Bulletin (Nov. 24, 1937), Academy of Motion Picture Arts & Sciences, Hollywood, 
Calif, (cf. p. 5). 


MR. GOLDSMITH : It is very obvious from these interesting curves which have 
been presented with unusual completeness that engineering compromises must 
be made in reproducing-equipment design in order to give reasonably uniform 
results in the theater for all types of product and on an economic basis. If the 
engineer were to specify "perfect" acoustics from zero cycles to the highest fre- 
quency which we hear, it would require that the theater be correct architecturally 
and acoustically, that the film be kept in immaculate condition to eliminate all 

Feb., 1939] 



film noises, and that other ideal conditions must hold. Inasmuch as the condi- 
tions which are encountered in actual practice can not approach the ideal, broad 
compromises must be made. It would be interesting to know whether these 
performance curves have been selected as a matter of engineering judgment, in 



X s 



300 //rc 



FIG. 11. Overall system acoustic characteristic. 

Lview of economic conditions and considering what studios, theaters, and a vail - 
i able recording and reproducing equipment could and would do, and what quality 
| of sound film can reproduce without excessive maintenance. 

MR. FRIEDL. Yes, it is true that these curves have been established with 
that practical consideration. In continuing this study of overall performance, the 





FIG. 12. Overall system acoustic characteristic. 


end result that is, bringing to the patron in the theater a better record or re- 
production of the original we urge more sincere cooperation of the recording, 
processing, and reproducing-equipment groups. 

Just as the "Recommendations on Theater Sound Reproducing Equipment" 
(prepared by the Research Council of the Academy of Motion Picture Arts and 
Sciences), as read before the Society in Washington, outlined many desirable con- 
trol factors, we would like to follow up and urge control factors in other links of 

182 F. DURST AND E. J. SHORTT [j. s. M. P. E. 

the chain. At the present time the manufacturer of the theater equipment 
bears the responsibility of making acceptable to the patron the product delivered 
to the projection room in the film can. There is a certain latitude and limit to how 
much the projectionist or the sound reproducing equipment can compensate for 
recording and processing variations, particularly inasmuch as economies are re- 
garded more consciously at the theater end of the chain than any place else in the 
industry. The composite chart that you saw at the beginning of the paper con- 
tains many more factors than we are able to discuss at this time. 

MR GOLDSMITH: Referring to Fig. 1, what is meant by the "lens characteris- 
tic"? Do you mean the high-frequency loss which results from the relationship 
between the slit width and the length of the recorded wave on the film? 

MR. DURST: Yes. This is a fixed loss. In addition, there are a number of 
other variables in most recording and reproducing systems. I have itemized a 
number of them in Fig. 2. 

MR. GOLDSMITH: This is a paper of a helpful type because it shows how much 
work remains to be done in system improvement, and frankly gives details. 

MR. DURST : It is an appeal in one respect to the industry to determine what 
type of characteristic is best, accept it as such, and lay it down in such a fashion 
that all concerned may work to it to their best advantage. It is very disturbing to 
find the very great differences that we do experience in the field. When a system 
is carefully tuned up for one picture, the quality of reproduction alters materially 
when the program is changed. 

MR. ROBERTS: I am interested in the small column in Fig. 1 entitled "Labora- 
tory." I would like a little more information on that one variation in high fre- 
quency. What does the 8-db. loss represent? 

MR. DURST: The variations that may occur in attention of the high-frequency 
response characteristic range anywhere from to 8 db. 

MR. ROBERTS: From laboratory to laboratory? 

MR. DURST: Yes, from laboratory to laboratory; or it is possible that it may 
vary to that extent in any one laboratory. 

MR. ROBERTS: In any one reel? 

MR. DURST: Not necessarily any one reel, but from one picture to another, 
or from one product to another. 

MR. WOLF: I was shocked that there was such an overall variation, and that 
the system had so much response in the low end. I would like to know a little 
more about the theater where this response was measured. I assume you con- 
sider the response curve about as fine a one as you know of in your practical ex- 
perience in the theater. Referring to the first curve, Fig. 3, the overall character- 
istic indicated rather uniform response except around the 150- to 400-cycle region, 
where it took a very decided dip for 4 or 5 db. and then went up again. 

That is, I take it, an overall acoustic characteristic, measuring the output 
acoustically in the theater. Is that right? 

MR. DURST: Yes. 

MR. KELLOGG : It is theoretically impossible to make up by choice of frequency 
characteristic, for such factors as monaural pick-up, difference between micro- 
phone distance, and the impression of distance that the theater patron gets, 
and the fact that most sound is reproduced at unnaturally high levels. Neverthe- 
less, there is unquestionably a frequency characteristic which on the average gives 

Feb., 1939] 



the best illusion, or, shall we say, makes the unnaturalness least conspicuous. 
This optimum characteristic no doubt depends on the factors just mentioned and 
others, but we do not know enough to figure it out. We must determine it by 
trial. It is simply a matter of taste. 


FIG. 13. Overall system acoustic characteristic. 

MR. DURST: That is very true. In this instance a single microphone was 
used and the nodal points were explored to obtain readings of maximum intensity. 
It is, for purposes of comparison, approximately equivalent to what might other- 
wise have been obtained with a warble frequency and fixed microphones. The 
measurements were made hi the auditorium approximately 40 feet from the 
speaker system. 

+ 3 

- 5 















*N X^*^ 













300 fKC 



FIG. 14. Overall system acoustic characteristic (Paramount Theater, Los 
Angeles, Calif., ERPI Mirrophonic system; one 86 amplifier and two 87 
amplifiers). Tests made by the Sound Department of Paramount Studio. 

MR. WOLF: How did you integrate the sound without a warble tone or 
multiple microphones? 

MR. DURST: By exploration of the wave pattern. 

MR. WOLF: You picked one point that did not seem to have any low points? 

MR. DURST: No, the microphone was moved until a maximum reading was 
obtained for each frequency reproduced from a standard constant-frequency film. 

184 F. DURST AND E. J. SHORTT [j. s. M. P. E. 

MR. WOLF: It was the average of several positions? 

MR. DURST: No; it was the maximum reading obtained at any point in that 
vicinity. It was not a predetermined position, but the wave was explored for the 
maximum peak or signal. 

MR. FRIEDL: As a matter of general interest, Figs. 11-16* show measure- 
ments in various theaters and also in a listening room, which were taken with 
a warble film and which would give comparable results. You will note a wide 
divergence of "end results," yet each of these represents a listening condition 
that is approved by a competent group of technical people. 

MR. WOLF: I never saw a group that agreed. 

MR. FRIEDL: A significant thing is the dip hi the region of 200 to 400 cycles, 
because it is in this band that various levels of energy might make dialog as pres- 
ently recorded sound very heavy. Such heaviness of dialog spoils naturalness 
and intelligibility. 

MR. GOLDSMITH: A "booming" effect may result if the energy is not attenuated 
in that region. 

MR. FRIEDL: These are all two-way systems. An interesting thing to note 
as you review dissertations and presentations on filter designs, is that they all 
refer to ideal designs. As a practical application, the designs are seldom used 
under the premises of the design, particularly with respect to impedance matching. 

MR. DEPUE: How was the laboratory work checked up on these tests? 

MR. DURST: Regular commercial prints were used for listening tests. Fre- 
quency measurements were taken with calibrated constant-frequency films 
and a warble film; also, oscillators were coupled to the input of the amplifier 

In the last illustration you will notice the absence of this dip of 250 cycles, 
that is, to the same extent as it appears in the other illustrations. This happens 
to be a studio listening room. The point I wish to bring out in this connection 
is that I believe it is important to the best interests of all concerned that the manu- 
facturers of theater equipment know what type of characteristic the producers 
are using in listening to their products. If we ever hope to make it possible for 
theater customers to hear the same things that the producers hear in their review 
rooms, we must have the same type of characteristic. The example given shows a 
decided difference from measured theater characteristics. If that is a desired 
characteristic or a necessary one for recording purposes, then all theaters should 
have the same. However, we find it quite the contrary in reproducing a wide 
number of film products. Filling in this dip does not give a most pleasing result. 

MR. HOVEY: Is that caused by acoustic conditions in the theater? I should 
think the first step would be to correct that. 

MR. DURST: The necessity of a dip in the region of 250 cycles is general, 
because of variations in recording practice with respect to dialog equalization. 
It is usually created in the reproducing characteristic by impedance mismatching 
or in the design of the low-frequency horns. It may be corrected by acoustical 
networks within certain limits. 

* With respect to Figs. 14, 15, and 16, appreciation for his cooperation is ex- 
pressed to Mr. L. Ryder, Director of Recording, Paramount Pictures, Inc., Holly- 
wood, Calif. 

Feb., 1939] 



MR. FRIEDL: It can also be done electrically with more flexibility, pro- 
vided we agree on what we are trying to achieve. There are several ways of 
doing it. We are all striving for uniformity in the presentation of our product. 

teumve SOUND wrfNsirr /N OB 
i t i i + 

01 8 5; S o, o o> 











\ , 











RCA #MBL fffeQ. FILM #^)e-l 





500 fffC 



FIG. 15. Overall system acoustic characteristic (Paramount Studio Sound 
Theater) . Tests made by the Sound Department of Paramount Studio. 

If we agree on what we want in the end, the studios will work cooperatively, and 
we should achieve the uniformity we desire. 

MR. HOVEY : The statement was made several times that this or that sound 
was satisfactory or good. I can not help wondering to what extent a state of 


























fOO 3CO fKC 



FIG. 16. Overall system acoustic characteristic (Paramount Studio Projection 
Room) . Tests made by the Sound Department of Paramount Studios. 

tone paralysis may enter into that. It has been my experience that when an in- 
stallation is made, those who are hi contact with it daily become, after a month or 
so, so sound paralyzed that even the most terrible sound seems all right to them. 
I wonder whether that is the experience of other engineers. 

186 F. DURST AND E. J. SHORTT [j. s. M. p. E. 

MR. FRANK: I might explain that by a story I have heard often about the 
Board of Directors of the old Victor Talking Machine Company. When the or- 
thophonic phonograph was demonstrated to them, they said, "That is wonderful, 
but it does not sound like a phonograph." It certainly has been our experience 
in theater work that the longer we listen to sound quality, irrespective of what 
the quality is, the better we think it is, and it is only by direct comparison and 
technical analysis that we begin to tell whether we are hearing what is supposed to 
be "good" sound or not. 

MR. HOVEY: Recently I witnessed an installation of what I considered un- 
usually good sound, and the theater manager ordered it out and replaced it with 
an outfit about five years old because, he said, it sounded better. It would be 
interesting to know whether that is an unusual case or whether other engineers run 
into the same thing. 

MR. GOLDSMITH: That is an unfortunately frequent case. In the early days 
of radio, there was once a controversy between the advocates of long horns and 
short horns, respectively, for loud speakers, the "long horns" stating that the 
loud booming response with practically no high frequency was admirable and that 
it was what they termed mellow and soothing; whereas the other group, the 
"short horns," insisted on suppression of low frequencies and emphasis on high 
frequencies until the result was a thin squeak. No agreement was ever reached 
between those two groups because each became confirmed in its conviction that 
its customary preference constituted ideal reproduction. There was no major 
progress until response curves were used as a guide to design. 

MR. FRIEDL: Another analogy might be that although there are some really 
good radios on the market today and high-quality radio programs are broadcast, 
the reproduction in the average home is poor because the sound is unbalanced by 
inaccurate adjustment of the tone control. 

We all desire to standardize theater equipment for high-quality reproduction. 
The companies interested in the production of films spend a lot of money to this 
end. It is their desire to control the quality without recommending the use of 
variable adjustments that would permit the projectionist to distort the balance 
of the frequency range with an adjustable tone control. Unless we can agree 
on a certain quality of performance and consistently control the variables that 
would disturb that quality, we are forced to admit that "good quality" is a matter 
of personal judgment. Thus: If a man who is running that theater wants to 
have it sound a certain way, a way that he feels satisfies his patrons, he will de- 
mand the same facilities as he uses in his home with his radio. After all, in the 
dubbing of a film there is a man who sits in a room where he listens and judges 
what he thinks is good reproduction. He might satisfy the directors; he might 
satisfy the producer and the studio personnel that he has done a good job. At 
the same time the deadline of the picture might be approaching or the budget 
running out, and that picture is going out to make money. The people in the 
theater end of the chain are supposed to correct all those ills. We hope the studio 
recording can be perfected to the point where we can eliminate that variable. 

MR. WOLF: The only criticism I would have to the overall response curve is 
that it shows too many factors, represents so many things that you do not know 
what is at fault. 


Where do you think the weakest link now exists? Is it in the theater acoustics 
or in the electrical system? Or is it still in the loud speaker system? 

MR. DURST: I believe that by careful manipulation of the characteristics, a 
given theater can be made to sound fairly satisfactory. Granted there are acousti- 
cal conditions that can not be compensated for electrically, as a general average one 
can make equipment sound right. But, if what is put on the film is not designed 
to be reproduced over that characteristic, it never will sound right. If a given 
theater is adjusted so that it sounds right for one film, the next one that comes 
into that house may be altogether different, and the service engineer has to go 
back and readjust or re tune the entire system to satisfy his customers. 

MR. WOLF: I still believe in the theory of the uniform characteristic in every 
element of the circuit from the microphone all the way through. A great many 
are getting away from that, thinking perhaps they can have compensating in- 
fluences in each element of the system, but I still think we will not get a uniform 
response until in the theater, we have uniformity in every piece of equipment. 

MR. DURST: I do not believe that is altogether desirable from the recording 
standpoint. Producers have such diversity of story material, and in their effort 
to reproduce the true dramatic effect, it would be rather difficult for them to have 
any fixed characterics, but I do believe that they must all work to an established 
end result. In like manner, I think the manufacturer of reproducing equipment 
should work to that same end result. It should be up to him to decide whether 
he wants to taper off his horn or whether he wants to change his slit size. If he 
can obtain a better signal-to-noise ratio and better overall compensation by one 
means or the other, I think it should be left to his discretion. 

MR. STROCK: I should like to say one word about all these variables that enter 
into the problem. In our own particular case, and I know it to be true in several 
of the other studios, what we do shows up only in what comes out of the horn 
in the theater, and we are continually checking the product that we listen to in our 
own theater from day to day against what it sounds like in the field. Of course, 
you have to define a "representative theater," but nevertheless it is a good theater 
that is generally accepted as giving good sound. After all, when you come down 
to saying whether sound is good or whether it is bad, our own definition of good 
sound is sound that comes out of a loud speaker that is natural and tempered by 
the perspective of what is going on in the picture; meaning that if you have a full 
head close-up of somebody saying some very touching and endearing words, you 
have to temper that by the size of the picture and the dramatics of the story. 
Nevertheless, good sound is natural sound. 

MR. WOLF : What you are after is a facsimile of the original in most cases. 

MR. STROCK: Not forgetting the picture. 



Summary. The addition of practical operational accessories to standard recording 
channels as purchased expedites operation and saves time. At the Eastern Service 
Studios a number of such accessories have been designed and are described briefly. 
It is the purpose of this paper to show what has been done at one studio in the hope that 
it may be of some interest and help to others who are engaged in recording work. 

Included in the equipment are the following items: A small collapsible, portable 
microphone boom for location work; a special microphone suspension to prevent me- 
chanical noises from getting into the recording system; a small mixer console for stage 
work, to permit the mixer man to operate close to the scene of action; an accurate 
illumination meter, using a microammeter, for setting and checking the recording 
machine exposure; a compact re-recording mixer console equipped with equalizers, 
effect filters, amplifiers, and attenuators; a projected volume indicator and footage 
counter for use in re-recording rooms; a film playback adapter for use on a Western 
Electric film machine for location use; playback horns for stage and location use; 
and an air-brush adaptation for blooping re-recording tracks. 

When recording channels are purchased they usually consist of 
several separate units following the general order and layout of the 
electrical schematic. The addition of certain practical operational 
accessories to these standard recording channels expedites operation 
and saves time. At the Eastern Service Studios a number of such 
accessories have been designed which are briefly described and illus- 
trated herein. It is the purpose of this paper to show what has been 
done in this studio in the hope that it may be of some interest and 
help to others engaged in recording. 

Portable Microphone Booms. The first unit to be described is a 
small portable, collapsible microphone boom. For regular studio use 
we have the standard, medium, and large types of Mole-Richardson 
booms. There are many instances where a small microphone suspen- 
sion is needed such as in pick-ups from a theater stage, small attic 
rooms, narrow hallways, etc. We have two types, one a very simple 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 17, 

** Eastern Service Studios, Long Island City, N. Y. 






[J. S. M. P. E. 

one and the other a bit more versatile but not complicated. The 
smaller one (Fig. 1) consists merely of two telescoping duralumin rods 
mounted on a yoke which is equipped to fit in a standard light stand. 

This is, of course, useful only for 
stationary shots. The general 
purpose small boom is shown in 
Fig. 2. It may be extended or 
retracted, lowered or raised noise- 
lessly at will, and it is easily 
moved for trucking shots. It 
may be locked in any position by 
friction by the handle. It is 
easily dismantled for packing in 
the location trucks. Its total 
weight is about fifty pounds. 

Microphone Suspensions. 
Most microphones are subject 
to the disadvantage of convert- 
ing mechanical shocks into elec- 
trical noises in the recording sys- 
tems. The standard mountings 
(Fig. 3) for either the Western 
Electric 630 or 618 microphones 
do not provide for any shock 
absorbing medium between the 
microphone and the boom or 
support. Such an absorbing 
medium is necessary when mov- 
ing the microphone rapidly dur- 
ing the recording. Microphone 
noise is largely due to mechani- 
cal noises within the boom being 
transmitted directly into the 
microphone. To help eliminate 
this direct transmission, a short 
flexible lead (Fig. 4) is provided 
between the boom cable and the microphone. This connector is 
usually made from telephone tinsel or other very flexible stranded 
wire and has proved very satisfactory. A retaining cord must be 
provided to avoid excess strain on the fragile tinsel leads. 

FIG. 3. ( Upper] Standard microphone 

FIG. 4. (Lou'er) Showing flexible 
lead between microphone boom cable 
and the microphone. 

Feb., 1939] 



The microphones are supported in several different types of mount- 
ings all of which are satisfactory from a noise standpoint. Shown in 
Fig. 4 is the mounting for the 630 microphone. Note that the mi- 
crophone is held in a yoke which is supported by standard Lord rub- 
ber mountings for reducing mechanical shock to the microphone 

FIG. 5. (Upper) Mounting for 618 microphone. 

FIG. 6. (Lower) Mounting for 618 or 630 


proper. In Fig. 5 is the mounting for the 618 microphone. In this 
mounting the shock is absorbed by supporting the microphone in a 
ring held by elastic. In Fig. 6 is shown a mounting which may be 
adapted to either the 618 or the 630 microphone. All these mount- 
ings, when used in conjunction with the flexible connector, prevent 
mechanical noise from being transferred to the electrical recording 

192 R. O. STROCK [j. s. M. P. E. 

Mixer Consoles. Most present-day motion picture voice recording 
is monitored and mixed from a small mixing console which can be 
placed close to the set or scene of action, as shown in Fig. 7. The 
advantages of the mixer man's being in close contact with the director 
and the cameraman and in such a position that he can at all times 
watch the action far outweighs the disadvantages, if any, of head- 
phone monitoring. No loud speaker in a small monitor booth can 
equal theater characteristics. The mixer man must make a personal 
judgment between what he is hearing when recording and what he 

FIG. 7. Small mixing console on set. 

will hear in the finished sound in a theater. Therefore, he might just 
as well make his judgment between what he hears in the loud speaker 
compared to the theater horns as between a booth loud speaker and 
the theater horns. 

Mixer consoles, as used at Eastern Service Studios, are as shown in 
Fig. 7. They are small and can be moved easily when the company 
moves to another set. A three-position mixer is used and has been 
found adequate for most ordinary picture work. The mixer is con- 
nected to an amplifier, and the combination is known as an ERPI RA- 
150, which is battery operated and uses electronic mixing. 

Feb., 1939] 



The mixer is so connected that if it is necessary to move quickly to 
a nearby set for a pick-up shot, the mixer panel can be easily removed 
and carried to the location without moving the console. It is pos- 
sible to work the mixer 300 feet away from its amplifier. 

On the panel board (Fig. 7) are shown the mixer, the telephone for 
interstage communication, and the signal lights for the recording 
system. The amplifier is housed in one end of the console and the 
battery equipment in the other. In the rear is space for storing the 
microphone cable. 

FIG. 8. General layout of re-recording mixer 

Projected Volume Indicator and Footage Counter for Use in Re-Re- 
cording. The next unit to be described is the re-recording mixer con- 
sole. This is very similar to the stage pick-up unit but is used for the 
re-recording process and is a bit more complicated. Fig. 8 shows its 
general layout. The circuits are brought from the re-recording 
machines through the jack field on the end of the table and then 
through the mixer and into a main amplifier. The amplifier is a-c. 
operated and is mounted on a swinging hinge so it may be swung out- 
ward for changing tubes or for servicing. Equalizers, attenuators, 
telephone effect filters, high- and low-pass cut-off filters, and a uni- 
versal high- and low-frequency equalizer are provided so they may 
be inserted in any desired mixer position for changing the circuit fre- 

194 R. O. STROCK [j. s. M. p. E. 

quency characteristics. A level control is provided on the output of 
the amplifier for controlling general level into the recording rooms. 
Re-recording mixer men must first be artists, and second engineers, 

FIG. 9. Projected volume indicator and footage counter. 

FIG. 10. Showing arrangement of volume indicator and 
footage counter. 

for in the mixing of many sound-tracks into a composite effect, recog- 
nition must be made of cueing, levels, artistic effect required by the 
director, perspective, and geography of the scene at hand. In order 


to aid the mixer man in doing so many things at one time, and in addi- 
tion, not divert his attention from the picture, a projected volume in- 
dicator and footage counter has been built. As can be seen in Fig. 9, 

FIG. 11. Footage counter. 

the volume indicator and footage counter images are projected to a 

considerable size directly below the picture, so it is possible for the 

mixer to see with ease the footage for spotting cues, the sound volume, 

and the picture, all at the same time. 

If the volume indicator is used on the 

re-recording table it is very difficult and 

tiring to try to change the line of sight 

between the picture and the volume 

indicator rapidly. This unit has been a 

great help in re-recording. 

Fig. 10 shows how simply this has 
been accomplished. The volume indica- 
tor is placed on the rear of a standard 
Keystone postcard projector and its 
image projected upon the screen. Two 
100- watt lamps are used to illuminate 
the meter and no difficulty from heating 
is experienced, the lamps remaining on 

for several days at a time during long 

J 6 FIG 12. Illumination meter, 

re-recording sessions. 

The footage counter also is shown in Fig. 10. A special Veeder 
counter, with the numbers upside down, was mounted on an inter- 
locked motor which is electrically connected to the recording dis- 



[J. S. M. P. E. 

FIG. 13. Recording machine with illumination meter attached. 

FIG. 14. Recording machine before being adapted for 

Feb., 1939] 



tributor system the same as the recording and projection motors. 
The counter (Fig. 11) is illuminated by a 100- watt screw-base lamp 
with a condenser lens, and its image is projected upon a screen directly 

FIG. 15. Playback adapter. 

FIG. 16. Playback adapter unit mounted on the machine. 

below the volume indicator image (Fig. 10). The counter is easily 
reset and the volume indicator meter can be removed easily for re- 
placement if necessary. 

Illumination Meter for Checking Recording Machine Exposure. In 
order to control the quality of sound recording it is necessary to main- 



(J. vS. M. P. E. 

tain the recording machine exposures very accurately. Ordinary 
ammeters in the lamp circuit can not be read accurately enough to 
control the illumination within the necessary limits. Our standards 

require that the negative expo- 
sure be held within 0.05 in 
visual diffuse density. In order 
to hold the exposure within 
this rather narrow limit an ac- 
curate illumination meter was 
designed, as shown in Fig. 12. 
It consists of a plate which can 
be clamped quickly on the re- 
cording machine (Fig. 13). On 
the plate is mounted a metal- 
lic mirror which intercepts the 
light-beam just in front of the film and reflects the light into a 
photoelectric cell mounted in the round container on the front 
of the plate. The photoelectric cell has low sensitivity and 

FIG. 17. Blooper. 

FIG. 18. Another design of blooper. 

is operated in the very stable portion of its sensitivity curve. It is 
connected to a 0-2jia Rawson microammeter and a normal current of 
approximately 0.75 microampere flows through the photoelectric cell. 
An exposure test is made for the particular emulsion in use and the 


correct density is determined in the usual manner from the negative 
H&D curve, after which a curve is made plotting density against 
microammeter readings, and the correct reading obtained. The il- 
lumination can be checked very rapidly by the use of this instrument 
and it is the usual procedure to check the exposure after every five 
takes. The instrument has been in use for several years and has 
proved very satisfactory, showing that the exposure can be main- 
tained within the 0.05 density limits for months at a time. 

Film Playbacks for Location Trucks. It is often necessary to use 
film playbacks on location. The standard D 867 15 Western Electric 
recording machine for location trucks is not equipped for playbacks. 
One of our machines in a location truck has been modified so that it 
can be used for either recording or playback purposes. In Fig. 14 
is shown the recording machine before adapting it to playback. In 
Fig. 15 is shown the adapter. It consists of two arms for holding the 
supply and take-up reels and a means of driving it. In Fig. 16 the 
unit is shown mounted on the machine. A photoelectric cell is placed 
inside the recording sprocket and its ______ _~ 

output fed through a low-capacity 
cable to the regular split-beam 
monitoring unit, whose output is 
fed through the recording amplifiers 
and then into a playback horn. The 
unit can be removed and the ma- 
chine returned to the recording FlG - 19 - Blooper of Fig 18 with 

plate in place over film, 
condition in only a few minutes by 

removing two thumb-screws and removing the drive belt. The film 
can be rewound without removing the reels from the machine. 

Air-Brush for Blooping. In re-recording it is very necessary that 
bloops caused by splices be entirely eliminated. We use two types of 
"bloopers." One is as shown in Fig. 17, described by E. I. Sponable 
some time ago. This unit does the job very well. We have designed 
another unit that does the job equally well and is shown in Fig. 18. 
It consists of a block and template with centering pins and an air- 
brush for spraying the blooping ink on the template and the splice. 
Rapid drying ink is used. In Fig. 19 is shown the plate in place over 
the film. The template provides assurance that the edges of the 
bloop are sharp and, because the back of the film is pressed against 
rubber, good contact can be obtained between the template and the 
film. The design of the bloop patch is the same as the one described 

200 R. O. STROCK 

by Sponable. This unit can be constructed very easily, and a stand- 
ard air-brush and tank are used. 

The accessories described above have been a great help to this 
studio in its operation. It is hoped that others engaged in recording 
work will describe their many operational accessories from time to 
time in the JOURNAL. 

Credit for the design and suggestions on the units just described is 
given to our recording staff in general and in particular to Dan Don- 
caster, our mechanic, who built and suggested many of the items. 



Summary. Here and there a theater is planned with lighting features utilizing the 
fundamental principles that have been expounded on many occasions. In too many 
cases, however, interior lighting has lagged far behind exterior lighting for advertising, 
and owner and public alike have suffered. In too many cases, also, the theater falls 
far short of complementing the attractive scenes so well projected upon the screen. 

This paper reiterates the aims and advantages of proper lighting, and outlines the 
problem of locating, and controlling the lighting properly so that it will be comfort- 
able and pleasing and an aid, psychologically. 

Because of the almost infinite variation in design for theater audi- 
toriums, with influences all the way from cave-dwellers to the ultra- 
modern, and from the bottom of the sea to the sky above, practically 
every conceivable lighting method or idea has been called into play. 
Unquestionably architectural influence and decorative character have 
played a far more important part than the provision of light for com- 
fortable and safe seeing. 

The purposes of auditorium lighting are several and varied. In 
this investigation we are chiefly concerned from the viewpoint of com- 
fortable vision and how to provide for it while serving these other re- 
quirements as well. This paper presents experimental data applying 
to a limited range of auditorium conditions. Although by no means a 
comprehensive treatment, it does offer a little additional information 
in a field where quantitative studies have been badly needed. 

In order to visualize the complete picture of the objectives of audi- 
torium lighting as set forth on previous occasions li2 ' 3 - 4 they are re- 
peated here : 

(1) Comfortable Vision. Eyes should be aided in their adjustment to darkened 
interiors and made comfortable by adhering to brightness standards. 

(2) Convenience. People must see quickly and easily to locate seats, without 
annoyance to others and without individual usher service which is expensive. 

*Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 
19, 1938. 
**General Electric Company, Cleveland, Ohio. 




[J. S. M. P. E. 

(3) Safety. Light dispels the fears that patrons may feel in darkened theaters. 
Accidents and accident costs are also reduced. 

(4) Program Appreciation. Decorative lighting provides a "plus" value that 
secures a favorable psychological reaction, and is of aid in counteracting seasonal 
temperature complexes. It aids special programs or holiday celebrations and 
creates a mood that aids program appreciation. It makes people look better and 
feel better. 

(5) Cleanliness. Light reveals a clean theater. 

As previously stated, it is desirable to give consideration to all 
these factors in lighting an auditorium, but this paper will deal pri- 
marily with the one factor of ocular comfort as affected by the quan- 
tity and direction of light and the location of sources, their brightness 
and that of the several parts of the visual field. 

c o 

i ii ii ii ii inn 




















oo r o >> o 






/ ^ 



O Q^ o 13 0*0 









FIG. 1. Auditorium layout with illumination systems used in tests. Letters 
refer to locations measured for brightness. 

In the past we were handicapped by the lack of a convenient and in- 
expensive brightness meter that would permit ready recording and 
analysis of brightness conditions throughout an auditorium as viewed 
from any given seat. Some years ago the SMPE Theater Lighting 
Committee 10 devoted much study to the characteristics of such an 
instrument. This need has been expressed in many Committee re- 
ports from time to time. Today, this need is met by the Luckiesh- 
Taylor brightness meter. 5 It is possible to focus the instrument on a 
very small spot, and accurately determine the brightness of that spot 
over a range exceeding that found in theaters. The brightness is 
read directly in candle-power per square-inch, or in the more readily 
comprehended foot-lambert. 


The foot-lambert may be defined simply as the brightness of a 
perfect diffuser emitting one lumen per square-foot. Or, assuming 
perfect diffusion, the foot-lambert is the brightness resulting from the 
product of foot-candles illuminating a surface multiplied by the re- 
flection or transmission factor of the surface. Hence it is sometimes 
referred to as foot-candle on white. 

The tests conducted by the authors were made with six experienced 
observers in the auditorium of the Lighting Institute of Nela Park. 
The dimensions of this auditorium are 46 feet by 34 feet and the seat- 
ing capacity is 250. Fig. 1 illustrates the auditorium layout and loca- 
tion of test positions. The small size of the theater will, of necessity, 
serve as a limit in the application of results to large theaters. 

The lighting systems used in the tests and located in this audi- 
torium have adequate thyratron and resistance control. They in- 
clude : 

(1) Six suspended indirect type luminaires. 

(2} Six luminous windows at each upper side wall with lighting directed toward 
the front part of the auditorium. 

(3} Six pin-hole objective-lens downlights directed at an angle of 20 degrees 
toward the front of the auditorium. 

(4) Stage borderlighting to light screen surroundings. 

(5) Aisle lights. 

To fix the test conditions as much as possible, tests were first made 
with a slide picture having light and dark regions fairly evenly dis- 
tributed. The picture was 71 inches wide by 51 inches high. The 
brightness of screen without picture averaged 14 foot-lamberts and 
the whites in the picture averaged 9 foot-lamberts. The principal 
test position was a side seat in the rear row which offered the most 
severe visual condition as far as ceiling and side-wall brightness was 

It is readily apparent that a still picture would become monotonous 
and distractions would be more in evidence than with a moving pic- 
ture. Some of the tests were accordingly re-run with a motion pic- 
ture, with a height of 46 inches and a width of 65 inches. At the 
principal test positions, 43 feet from the screen, the angle subtended 
by the screen was 7 degrees. The average brightness of the blank 
screen with projector lighted and shutter operating was 4 foot-lam- 
berts. With a picture the brightest whites were 3 foot-lamberts. 
The small size and low brightness of the screen are two of the limita- 
tions mentioned. 

204 F. M. FALGE AND W. D. RIDDLE [j. s. M. P. E. 

Experienced observers were selected and the objectives made known 
to them because this test was purely a visual one. It was interesting 
to note, however, how positive reactions were to visual discomfort, 
how close the reactions of various observers checked, and how close 
an agreement was had to earlier tests by others. 

Test No. 1 Lighting from Picture Alone. (Fig. 2) Observers con- 
cluded that a lighted screen alone was definitely uncomfortable due 
to glare, and very fatiguing, a conclusion supported by general ex- 
perience. 1 - 4 ' 6 Aisle lights did not aid appreciably in relieving this 

FIG. 2. Test No. 1 : Lighting from picture alone. 

condition. It was not possible in this test to evaluate the discomfort 
factor of entering such a darkened auditorium from regions of higher 
brightness, but experience in theaters lighted in this manner indi- 
cates that it is definitely uncomfortable and annoying. This is sub- 
stantiated also by previous investigations. In this case it is usually 
necessary to accompany patrons to seats with a flashlight, a procedure 
that is a rather poor seeing compromise and an expensive one. Aisle 
lights were of some help, due primarily to identification of aisles. 

It was noted that variations in screen brightness due to unequal 
distribution of blacks and whites caused wide fluctuation of illumina- 
tion on the ceiling and side walls that was distinctly annoying. This 


condition is accentuated when patrons wear light-colored summer 

Test No. 2 Illumination of Screen Surroundings. Previous in- 
vestigations have concluded that screen surroundings should pre- 
sent some brightness. Jones 4 arrived at the conclusion that the 
contrast with the immediate surroundings should be less than 1 to 
500 as compared with the brightest parts of the picture. O'Brien 
and Tuttle 7 concluded that the highest desirable brightness of the 
immediate surroundings is 0.8 foot-lambert and that the preferred 
brightness lay between 0.05 to 0.20. This provides a contrast range of 
Vioo to J /26 of the bright parts of the picture. Wolf 8 concluded that a 
border brightness of 0.047, providing a ratio of 1 to 100 with the 
brightest parts of the screen, was desirable. Schlanger 6 proposed a 
method of automatically varying this brightness with the picture. 

In their tests the authors wished to determine the desirable bright- 
ness of the field surrounding the screen rather than just the frame for 
the picture. Observers agreed that as surrounding illumination of 
fairly uniform brightness increased glare was relieved. With the slide 
on the screen, a brightness of surroundings was soon reached in which 
it was felt that the background began to compete with the screen it- 
self for attention. The unlighted border around the screen first be- 
came objectionable because of its extreme contrast with both screen 
and surroundings. When the screen was arranged so as to be im- 
mediately adjacent to the illuminated background this condition 
was relieved and a higher brightness of background was satisfactory. 
A brightness of background of l / Z6 to Vw of that of the screen was 
found satisfactory. However, although relieving the screen glare, 
little illumination was added to the auditorium to provide the com- 
plete comfort condition desired. 

Test No. 3 Upper Value of Desirable Illumination. It was felt 
that this upper limit might be set as the point at which the move- 
ments of other observers became disturbing and that, before deter- 
mining the quality or quantity of light desirable for comfort, it was 
necessary to determine this upper limit. This value was determined 
with a fairly comfortable system of lighting combining background 
illumination and indirect illumination from the suspended luminaires. 
With the slide, this value lay between 0.1 and 0.2 foot-candle. How- 
ever, the animation of the motion pictures tended to render less con- 
spicuous the movements of others, and values of 0.2 to 0.5 foot- 
candle were found to be satisfactory. 

206 F. M. FALGE AND W. D. RIDDLE [j. s. M. P. E. 

This condition was affected to a great extent by the color of clothes 
worn. At 0.5 foot-candle, medium or dark clothes were not readily 
noticed but light clothes were. The brightness of white clothes in this 
case was 0.35 foot-lambert. It can be concluded, therefore, that in 
the south, and during the summer when light-colored clothes are 
worn, levels of illumination should be somewhat lower. 

Test No. 4 Lower Value of Desirable Illumination. Determination 
of this lower value was more difficult and the factor of eye adapta- 
tion caused by entering the auditorium from regions of higher bright- 
ness had to be disregarded. The indirect lighting system was selected 

FIG. 3. Test No. 7: Downlighting. 

for this purpose. Starting with only the motion picture on the screen 
and gradually raising the level of illumination, it was found that re- 
lief from the glare of the screen came when the auditorium illumina- 
tion ranged from 0.05 to 0.1 foot-candle. Measurements were made 
in foot-lamberts with the brightness meter and the corresponding 
illumination values were calculated. 

Test No. 5 Indirect Lighting (Suspended Luminaires). With the 
screen surroundings having a brightness of 1 /w of the screen whites, 
several levels of indirect lighting were investigated. 

Feb., 1939] 



With 0.5 foot-candle in the auditorium, the upper limit reached in 
test No. 3, the lighting was fairly comfortable but with the following 
shortcomings : 

(1) The light falling on the screen measured 0.35 foot-lambert, which was 
enough to harm the picture contrasts seriously. 

(2} The brightness on the upper part of the proscenium due to the close 
proximity of the two front luminaires became somewhat disturbing. This 
brightness was 1.8 foot-lamberts. 

Objection No. 1 might be relieved somewhat by a shadow-box ar- 
rangement, and objection No. 2 by relocating the front luminaires. 

A second test was made with this 
same indirect system providing 0.25 foot- 
candle in the auditorium. Objection 
No. 2 was now overcome but the light 
spilled on the screen was still objection- 
able, as it measured 0.18 foot-lambert. 

Test No. 6 Luminous Elements (Win- 
dows) at Upper Side Walls. Because the 
junction of ceiling and side walls is farthest 
from the line of vision when viewing the 
picture, it was thought that it would be 
found that highest brightnesses would be 
acceptable here. Tests with the lighted 
windows substantiated this fact. How- 
ever, it was apparent that there was a 
decided distraction from a concentration 
of illumination at these positions which 
conflicted definitely with the screen. As 
a result, even though higher brightnesses 
did not appear glaring here, it was con- 
cluded that a low order of brightness, especially at the front of the 
auditorium, no higher than a brightness of 3 foot-lamberts should be 
used, which is in accord with the findings of Jones. 4 However, this 
brightness may be gradually increased toward the rear of the audi- 
torium as the subtended angle at the eye of screen and light-source 
becomes greater. Many theaters have as their sole source of 
illumination shaded side- wall brackets. With a good combination 
having two 10- watt amber lamps the brightest point measured 21 
foot-lamberts. Two 15- watt lamps gave a measurement of 65 foot- 
lamberts. The light oak background measured 8 foot-lamberts and 

FIG. 4. The downlight- 
ing system used in Test 
No. 7, which affords one of 
the best methods now 
available of directing and 
controlling light for audi- 
torium purposes. 

208 F. M. FALGE AND W. D. RIDDLE [j. s. M. P. E. 

with a white 31 foot-lamberts. These values are all above the one 
for comfort, indicating that this method of lighting is in general 

Test No. 7 Downlighting. (Fig. 3) As previously pointed out, 
the downlighting system in this auditorium was of the objective-lens 
type, and it was so directed as to direct light forward of the vertical 
(Fig. 4) . Brightness at the ceiling openings was low. 

With downlighting alone, illumination could be raised to a point 
providing 0.08 foot-candle in the auditorium before the brightness 
on the heads of persons in the beams directly beneath the units be- 
came disturbing. At other locations values of 0.2 to 0.25 foot-candle 
were satisfactory. At no point did illumination fall upon the screen 
so as to be discernible, and ceiling or side- walls were not lighted so that 
there was no objectionable brightness here. 

Test No. 8 Downlighting and Indirect Lighting. By adding 0.04 
foot-candle of indirect lighting the brightness of the direct downward 
light was relieved and the system was then quite comfortable. 

An additional test was made by adding 0.25 foot-candle of down- 
lighting to 0.25 foot-candle of indirect lighting to provide the maxi- 
mum of 0.5 foot-candle, and this system was very comfortable. Pic- 
ture quality was, however, impaired by spilled light on the screen 
from the indirect lighting. 

Conclusions as a result of these tests and others cited were as fol- 
lows for the given auditorium conditions : 

(1) A picture viewed without any auditorium illumination is definitely un- 

(2) A minimum illumination of 0.05 to 0.1 foot-candle is required to soften 
picture contrast with background. Variation of picture size and brightness, and 
auditorium size would doubtless influence this figure. Jones 4 found that an il- 
lumination of 0.1 foot -candle at the front and 0.2 at the rear of the auditorium 
is desirable, and this is checked by the report before the International Com- 
mission of Illumination. 9 

(5) A maximum illumination of 0.5 foot-candle is permissible from the stand- 
point only of distraction caused by the movements of other persons. 

(4) Some illumination x /25 to Vso of screen brightness is desirable for the 
immediate screen surroundings. Higher relative brightnesses were satisfactory 
at greater angles from the screen. At the outer edges of the proscenium, values 
of 2 to 3 foot-lamberts were permissible, and approaching the rear of the audi- 
torium considerably higher values are acceptable, depending upon their height 
above eye level. 

(5) Indirect lighting has many advantages for auditorium lighting because 
the light is spread so as to be low in brightness and because an illuminated ceiling 
adds to comfort. But it is desirable to control the light at the front of the audi- 


torium so that the brightness at points near the junction of ceiling and proscenium 
is below 2 to 3 foot-lamberts and the screen brightness contributed by spilled 
light is below 0.05 foot-lambert. 

(6) Concentration of light at the front side walls is distracting. Such sources 
should be kept below 3 foot-lamberts. Side- wall brackets are in general too bright 
for comfortable vision. 

(7) Downlighting by controlled beams of light needs to be supplemented by 
some indirect lighting. The combination of the two systems affords the best see- 
ing conditions of any investigated, minimizing, as it does, bright conflicting sources 
and spilled light on screen. 


1 LUCKIESH, M., AND Moss, F. K., "The Motion Picture Screen as a Lighting 
Problem," /. Soc. Mot. Pict. Eng., XXVI (May, 1936), p. 578 

2 FALGE, F. M., AND WEITZ, C. E.: "Theatre Lighting," Bulletin, Nela Park 
Engineering Department, General Electric Company. 

3 CAMBRIA, F., AND FALGE, F. M.: "Theatre Lighting, Its Tragedies, Its 
Virtues," Trans. Ilium. Eng. Soc., XXIV (Nov., 1929), p. 890. 

4 JONES, L. A.: "The Interior Illumination of the Motion Picture Theater," 
Trans. Soc. Mot. Pict. Eng., IV (1920), No. 10. 

6 LUCKIESH, M., AND TAYLOR, A. H.: "A Brightness Meter," J. Opt. Soc. 
Amer., 27 (March, 1937), p. 132. 

6 SCHLANGER, B.: "A Method of Enlarging the Visual Field of the Motion 
Picture," /. Soc. Mot. Pict. Eng., XXX (May, 1938), p. 503. 

7 O'BRIEN, B., AND TUTTLE, C. M.: "An Experimental Investigation of Pro- 
jection Screen Brightness," /. Soc. Mot. Pict. Eng., XXVI (May, 1936), p. 505. 

8 WOLF, S. K.: "An Analysis of Theater and Screen Illumination Data," 
J. Soc. Mot. Pic. Eng., XXVI (May, 1936), p. 532. 

9 Report of the (Japanese) Secretariat Committee, Proc. Internal. Comm. 
Ilium., Cambridge (England), 8th Session (Sept., 1931). 

10 Report of the Theater Lighting Committee, /. Soc. Mot. Pict. Eng., XIV 
(Feb., 1931), p. 239. 


MR. CRABTREE : The spots on the ceiling were somewhat annoying to me. 

MR. FALGE: The picture does seem to give that impression. In the actual 
condition you would not see the spots or would not be conscious of them 
because they are well located. When there is a vertical cut-off and the eyes are 
not in the beam of the light the result would not be glaring. The illustrations 
do not give the proper impression. 

MR. SCHLANGER: It is unfortunate that so careful a study was not made in a 
room having more suitable lighting arrangements. The direct-indirect type of 
lighting fixtures suspended from the ceiling are glare spots in the patrons' field 
of vision. The glass panel on the underside of the suspended fixtures in the direct 
lighting portion is the most disturbing element; however, the indirect light com- 
ing from the tops of these isolated and suspended fixtures is also objectionable. 

210 F. M. FALGE AND W. D. RIDDLE [j. s. M. P. E. 

Apparently the authors used these fixtures merely to help determine illumina- 
tion levels, and they were not intended for recommended use. There are systems 
of indirect lighting that are more adaptable to this use; however, the use of 
secondary illumination of any kind during a screen presentation is debatable. 
The elimination of glare spots and contrasting levels of illumination during the 
screen presentation are exceedingly important. I have found that the general 
level of illumination can be increased to a surprising degree when the surfaces 
presented to the eyes are uniformly illuminated and devoid of all patterns caused 
by highlights, shadows, or contrasting decorations. 

Secondary illumination of the auditorium surfaces during the screen presenta- 
tion is most costly if carried out properly because the surfaces are usually dark 
enough to absorb screen light, thereby diminishing the efficiency of other forms 
of lighting. It seems that for greatest economy and simplicity, light surfaces 
reflecting the screen light would be efficient provided the reflections were con- 
trolled by the texture or angularity of the surfaces. Mr. Falge, what are the in- 
tensity and color of the walls of the auditorium where the tests were made? 

MR. FALGE: Light ceiling and side walls, and a very light oak panelling on 
the lower side wall. The color: light oak finish, a sort of tan. 

MR. SCHLANGER: I have had experience with theaters where the walls were 
pure white as well as where they were darker. Surprisingly enough, in some of 
the theaters where the walls were pure white the effect was not as objectionable 
as might be expected. If all the screen light reflected from surfaces is returned 
to the viewers' eyes an annoying flicker would result. To avoid this the texture 
or angularity of the surfaces could be such as to reflect a greater part of the light 
so that it falls upon the heads and sides of the viewers, leaving a small percentage 
of the light to reflect to the eyes. This would provide desirable diffuse lighting 
of the audience, and would also light up the wall and ceiling surfaces enough to 
avoid sharp contrast between the picture and the auditorium surface light. 

A certain amount of secondary light can be used in addition to reflected screen 
light. Such secondary light-sources must be located on wall or ceiling surfaces 
that do not fall within the field of vision of the audience. The type of secondary 
lighting so employed would be optional, only efficiency and appearance being the 
important considerations. Direct lighting sources more efficient than the indirect 
can be successfully used. The secondary lighting serves also as emergency light- 
ing in the event of a break in the screen light. 

Motion picture theater auditoriums have been and are being designed ac 
cording to Spanish, Aztec, or Modernistic inspirations. Such forms are unsuited 
to the purpose of the motion picture theater for two basic reasons. First, such 
decorations, which necessarily consist of forms creating shadows and highlights 
and differences in color and intensity in paint design, create the disturbing con- 
trasts referred to before; second, such decoration quite often becomes an 
unsuitable setting for the subjects of the films. 

It is possible to create an abstract form of decoration, using as inspiration such 
textures and angularities of surfaces as will properly react to screen light. 

It should be pointed out that the screen size in relation to the auditorium size 
referred to in these tests was rather small, and therefore the factor of screen light 
was not fully accounted for. 

MR. FRANK: Has any study been given to the color of light most desirable in 


a theater, or the use of fluorescent lights in auditoriums? Also, have any studies 
been made as to desirable aisle lighting? 

MR. FALGE: With regard to Mr. Schlanger's questions, the under surface 
of the suspended luminaires was a source of annoyance and should have been 
omitted. The system was not the best one for indirect lighting, and much im- 
provement could be made on it. As to the current consumption, there is consider- 
able misunderstanding on the part of many theater operators as to what consti- 
tutes current consumption. I have visited theaters that had side-wall brackets 
with one bulb in each bracket and a total of about 100 watts for the auditorium 
lighting, and have been told, "I want my lighting improved, but I do not want 
to use any more current." Theater operators are inclined to think of their 
lighting bill as their projection bill. They forget that perhaps the greater por- 
tion of the bill goes into projection and that the few lamps mentioned above 
amount to very little. 

With systems such as downlighting, and with better application of color and 
more efficient light-sources and equipment, it is feasible to light an auditorium 
economically to the low levels about which we are talking. It is the higher levels 
needed for intermission lighting that require more current, and yet the lights are 
used for such a short space of time that they are not excessively costly. 

Mr. Schlanger's suggestion of reflecting the screen light from the side walls is 
worth considerable study. The light can be utilized as he suggests, and it would 
be interesting to see whether it could be done practically. 

As to the suggestion that the theater auditorium should be entirely simple, 
with no special decorations at all, there is some question on that score. I listed 
other factors that are still of importance to the theater manager and owner. 
The patrons react to lighted interiors in other ways, even though our study was 
devoted primarily to seeing. 

Referring to Mr. Frank's question, we could not go into the study of color 
this time. It is a difficult study to make, the conditions are difficult to stabilize, 
and reactions are very difficult to get. That is a problem for the future, and an 
important one. However, we have studied the color of light as it relates to the 
efficiency of systems. Fluorescent lighting has great possibilities for theater 
interiors because of the extremely high efficiency that is attainable. With the 
green, for instance, we get 60 lumens per watt, whereas with the regular green 
lamp only one lumen per watt. We can get efficiencies up to 100 times as much 
as with the usual colored light-sources. 

Aisle lighting was included in our study. With little lighting in the auditorium, 
aisle lighting does help to identify the aisles, which seems to be its primary aim. 
However, with some of these other systems, well planned downlighting is 
used over the aisles, and in that case the aisle lighting is brought out very ex- 
cellently through that means. 

MR. CRABTREE : I think the keynote of this paper and discussion is to avoid 
distraction. If we could only get that idea over to the architects and publicize 
it to the same extent that the report of the Projection Practice Committee is being 
publicized, we would really be getting somewhere. In Rochester one of the 
principal theaters has just been redecorated, and apparently the management is 
highly pleased with it; but when you go downstairs and sit under the balcony 
there are glaring lights almost as intense as those from the side walls blazing into 


your eyes, so that enjoyment of the picture is impossible. It is quite apparent 
therefore that some architects are absolutely ignorant of the fundamentals in- 

As I have said before, to me the ideal condition is a completely darkened room. 
Experiments have shown, however, that the general level can be raised tre- 
mendously before the visibility of the picture is impaired, and under those 
conditions I do not think you need aisle lighting. In the rear-projection theaters, 
the general level is tremendously high, but the contrast of the picture is pleasing 
and adequate. 

MR. FALGE: I think Mr. Crabtree's comments are absolutely right. That 
is the keynote of everything we have found. Eliminate distraction and you are 
much nearer a condition of comfort. 

MR. WOLF: It is impracticable, however, to have complete darkness. 

MR. FALGE : I think it is. 

MR. CARLSON : I agree with Mr. Crabtree that the elimination of distracting 
influences is certainly necessary. Another way of expressing it would be that we 
are interested primarily in maintaining low differences in brightness. In other 
words, as in rear-projection theaters, a relatively high general level of illumination 
may be not only acceptable but actually pleasing, so long as there are no sources 
of excessive brightness in the field of view. 

MR. SCHLANGER: I have tried out some fairly successful indirect systems in 
theaters, for use during the screen performances, that have not proved distracting. 
Unfortunately, these systems are used only during intermissions, because the 
theater operators have found them expensive for continuous operation. For 
best results, indirect lighting must be continuous and uninterrupted. Indirect 
lighting is inefficient because of the amount of light that must necessarily be 
trapped. For these reasons, it is too costly for daily operating periods of ap- 
proximately eleven hours. 

The special holiday or other decorative lighting effects to which Mr. Falge 
refers are desirable, and can be incorporated in a built-in manner in any lighting 
scheme, but such lighting is intended purely for intermissions and would be 
highly distracting during screen performances. 

With regard to Mr. Crabtree's statement about the rear-projection theaters, 
I have found that regular front-projection theaters can be illuminated to levels 
as high as or higher than the levels found in the rear-projection theaters. 



(As a result of additional tests and consideration of field operating conditions, 
these Revised Specifications are recommended to supersede the original Specifications 
of March 31, 1937, and the subsequent Specifications of June 8, 1937.) 

Systems to Which These Specifications Apply: The two-way repro- 
ducing systems for which these characteristics are recommended, are : 

Type 7 ERPI Mirrophonic Systems M-101, M-l, M-2, and M-3 
using 594-A loud-speaker units (metal diaphragm) and TA-4181-A 
low-frequency units, M-4 using 555 loud-speaker units (metal dia- 
phragm) and TA-4181-A low-frequency units, and M-5 using 555 
loud-speaker units (metal diaphragm) and T A -4194 low-frequency 

Type II RCA system using M. I. -143 5 (metal diaphragm) and 
MJ.-1432-A low-frequency mechanisms. 

Type III Lansing equipped system using 284 or 285 (metal 
diaphragm) and 15X low-frequency mechanisms. 

Type IV RCA system using M.I.-1428-B or M.I.-1443 (non- 
metallic diaphragm) and MJ.-1432-A or M.I. -1444 low-frequency 

Measurement Point: These characteristics are valid for measure- 
ments made at the output of the power amplifier, including the 
low-pass filter, with a resistance equivalent to the speaker load, 
using the Academy Research Council Standard Multi-Frequency 
Test Reel (corrected),! and are subject to modifications to fit special 
acoustic conditions which exist in many theaters, due to the fact 
that the reverberation time or other acoustic characteristics are not 

* Reprinted from Technical Bulletin, Research Council, Academy of Motion 
Picture Arts & Sciences, October 10, 1938. 
** Hollywood, Calif. 

f The correction factors indicate the deviation from constant percentage 
modulation for each frequency. 



The above Academy Research Council Test Reels have been com- 
pared to both the Altec ED -20 (corrected),* and the RCA test film 
(Catalogue No. 26571), and all these reels should give approximately 
the same characteristic on any one equipment. 

Extensive field tests indicate that equipment set to these Standard 
Electrical Characteristics will give optimum reproduction of current 
studio recordings under all conditions. 

It has also been found that the calibration of individual frequency 
reels in use in the field varies in some instances. In case results 
obtained from any of these reels are obviously in error, the calibra- 
tion of the test reel used in making the run should be checked. 

Acoustic Correction: Whenever such conditions exist that the 
particular characteristic recommended does not give satisfactory 
results (after the calibration of the reel used for the frequency run 
has been checked), it is recommended that the acoustic characteristics 
of the auditorium be corrected. 

Mechanism Adjustment: With the available equipment as specified, 
operating with the Standard Electrical Characteristic, it is necessary 
in some instances that the sensitivity of the high- and low-frequency 
band be relatively adjusted to obtain a flat acoustic response on 
both sides of the cross-over. This adjustment usually takes the form 
of attenuating the high-frequency band, the amount of this attenua- 
tion depending upon the relative efficiency of both low- and high- 
frequency units and the specific properties of the auditorium involved. 

Typical values are as follows : 

Type I ERPI Mirrophonic systems, M-101, M-l, M-2, M-3, and 
M-5, attenuate the high-frequency band 2 to 4 db. 

Type I ERPI Mirrophonic system, M-4, attenuates the high- 
frequency band to 2 db. 

Type //RCA systems, M. I. -1435 and M.I.-1432-A, attenuate 
the high-frequency band to 2 db. 

Type III Lansing equipped systems attenuate the high-frequency 
band to 2 db. 

Type IV RCA systems, M.I.-1428-B, M.I.-1432-A, M.L-1443, 
and M.I.-1444, attenuate the low-frequency band to 2 db. 

Note: It should be remembered that the type and condition of 
screen used in the theater will in a measure affect the high-frequency 
response of the reproducing system. 

Tolerance: A tolerance of ==1 db up to 3000 cycles, increasing 
progressively with frequency to ==2 db at 7000 cycles, is the maxi- 
mum permitted for the following gain-frequency measurements. 



S S 3 Si 


FIG. 1. Revised Standard Electrical Characteristic for two-way reproduc- 
ing systems using metal diaphragms; Types I (M-101, M-l, M-2 Systems), 
II, and III. For optimum results with current studio sound recordings Type 
I, II, and III Systems equipped with metal diaphragm speakers should be 
adjusted to this Revised Standard Electrical Characteristic. 

S S 3 Si 

i ! S i S Mil 

FIG. 2. Standard Electrical Characteristic for two-way reproducing systems 
using metal diaphragms ; Type I (M-3 Systems) . This characteristic for Type 
I equipments (M-3 Systems) has not been changed, and remains as specified 
in the original publication of March 31, 1937, and the subsequent publication 
of June 8, 1937. 

Electrical Runs, Measured at the Output of the Power Amplifier with a Resistance 
Equivalent to the Speaker Load Using the Academy Research Council Standard 
Multi-Frequency Test Reel (Corrected), Altec Test Film (ED-20, Corrected), or 

RCA Test Film (Catalogue No. 26571) 

The tolerances of 1 db. up to 3000 cycles, increasing progressively with fre- 
quency to a maximum of =*=2 db. at 7000 cycles, should be rigidly maintained in 
adjusting equipment to these specifications. 

Electrical Runs, Measured at the Output of the Power Amplifier with a 
Resistance Equivalent to the Speaker Load Using the Academy Research 
Council Standard Multi-Frequency Test Reel (Corrected), Altec Test Film 
(ED-20, Corrected) , or RCA Test Film (Catalogue No. 26571) 

The tolerances of 1 db. up to 3000 cycles, increasing progressively with 
frequency to a maximum of =*=2 db. at 7000 cycles, should be rigidly main- 
tained in adjusting equipment to these specifications. 



II ill 

S 8 I 

i i i nil 

FIG. 3. Revised Standard Electrical Characteristic for two-way repro- 
ducing systems using metal diaphragms; Type I (M-4, M-5 Systems). For 
optimum results with current studio sound recordings, Type I systems 
equipped with metal diaphragm speakers should be adjusted to this revised 
Standard Electrical Characteristic. 

I i i tiiil 

IN srcn PCX tccow 

FIG. 4. Revised Standard Electrical Characteristic for two-way repro- 
ducing systems using RCA non-metallic diaphragms; Type IV. For 
optimum results with current studio sound recordings, those two-way repro- 
ducing systems equipped with non-metallic diaphragm speakers (Type IV) 
should be adjusted to this revised Standard Electrical Characteristic. 

Electrical Runs, Measured at the Output of the Power Amplifier with a Resistance 
Equivalent to the Speaker Load Using the Academy Research Council Standard 
Multi-Frequency Test Reel (Corrected), Altec Test Film (ED-20, Corrected), or 

RCA Test Film (Catalogue No. 26571) 

The tolerances of 1 db. up to 3000 cycles, increasing progressively with 
frequency to a maximum of 2 db. at 7000 cycles, should be rigidly maintained 
in adjusting equipment to these specifications. 

Electrical Runs, Measured at the Output of the Power Amplifier with a 
Resistance Equivalent to the Speaker Load Using the Academy Research 
Council Standard Multi-Frequency Test Reel (Corrected), Altec Test Film 
(ED-20, Corrected), or RCA Test Film (Catalogue No. 26571) 

The tolerances of 1 db. up to 3000 cycles, increasing progressively with 
frequency to a maximum of 2 db at 7000 cycles, should be rigidly main- 
tained in adjusting equipment to these specifications. 


Since a new committee Chairman will be appointed for the year 
1939, the present Chairman has considered it desirable to place on 
record, for the guidance of future chairmen, a somewhat detailed 
account of the procedures involved in preparing the papers programs 
for our Semi- Annual Conventions, as follows. 

Committee Personnel. Experience has shown that an increasing 
number of the papers in our JOURNAL are being written by technicians 
in the studios and laboratories on the West Coast. In February, 1937, 
at the suggestion of H. G. Tasker, Past- President of the Society, a 
sub-committee of the Papers Committee was formed on the West 
Coast with W. A. Mueller as Chairman and L. A. Aicholtz as Secre- 
tary. Each of the major studios and laboratories was represented. 
This plan centralized the work of paper solicitation on the West 
Coast and has proved a very practicable arrangement. It is strongly 
urged, therefore, that future chairmen adopt a similar plan, so that 
there will always be an active and representative sub-committee on 
the West Coast. 

Other members of the general Papers Committee should be chosen 
from the leading industrial firms in the East and Middle West in order 
that a direct relationship will be established with the principal labora- 
tories and branches of the industry. Members should also be selected 
in Europe in those countries where cinematographic research programs 
are known to be in progress. Since the work of the Committee must 
be carried on largely by correspondence, the personnel should not be 
too large. 


Details of the work may be classified as follows in the order of time 
before, during, and after a meeting : 

(1) Copy for Journal Notice of the Meeting. The copy for a request 
for papers should be published in each issue of the JOURNAL for four 
months before the meeting. This copy should be prepared about one 
month after the close of one meeting. A typical notice is the follow- 

* Received December 28, 1938, 



ing one used for the 1938 Fall Meeting (Detroit, Mich., Oct. 31-Nov. 
2, 1938). This notice was printed on the inside cover of the JOURNAL 
for June, July, August, and September, 1938. 


Manuscripts of papers received by September 1st will be given immediate 
consideration by the Papers Committee and the Board of Editors, and the best 
will be selected and given preferred positions on the program of the Convention, 
with ample time for presentation and discussion, or about 30 minutes to one 

Titles and abstracts of all papers must be received by September 15th to be con- 
sidered for listing on the Preliminary Program. 

Two complete copies of each manuscript must be sent to the Chairman of the 
Papers Committee by October 1st, in order that the paper be listed on the Final 
Program for presentation. Manuscripts arriving after October 1st may, at the 
discretion of the Papers Committee, be scheduled on the Program to be read by 
title or substituted for other papers in the event of cancellations. 

(2) Preliminary Letters. (a) About three months before the meet- 
ing, all members of the Committee should be circularized by letter, 
giving dates of meeting, closing dates for titles, abstracts, and manu- 
scripts. Previous Committee correspondence should be studied and 
a summary given in each letter of any papers which have been held 
over from previous meetings. 

(b) A prospect file should be kept for each meeting and every pros- 
pect should be sent a letter of inquiry on the status of a paper for the 
next meeting. 

(c) The condition of the industry should be analyzed and letters 
sent to possible authors of papers on subjects of current interest. 

(d) A letter should be sent to each of the Vice-Presidents of the 
Society inquiring as to the possibility of reports from the Committees 
under their supervision. 

(3) Preparation of Authors' Form. This form may be mimeo- 
graphed. Copies should be sent to each member of the Committee 
about two weeks after the first letter with a letter of reminder. A 
typical form is attached to this report. As favorable replies are re- 
ceived from the letters sent to prospective authors, an Authors' Form 
should be sent out accompanied by a reprint of the Regulations of 
the SMPE Related to the Preparation of Papers for Presentation and 
Publication (J. Soc. Mot. Pict. Eng., 31, 215, Aug., 1938). Each com- 
mittee member and author should be informed of the necessity that 
abstracts be sent in by the date specified and that two copies of each 
manuscript must be delivered by the date indicated. 


(4) Abstracts of the Papers to Journal Editor. It is usually neces- 
sary to revise some of the abstracts as received from the authors, and 
all abstracts should preferably be retyped to give a desirable uni- 
formity of copy for the printer. Some abstracts are too long; some 
are written poorly as to sentence construction; and occasionally one 
is received that is advertising copy rather than an informative, con- 
cise statement of the author's paper. It is important, therefore, that 
every abstract be read carefully before release for printing in the 
JOURNAL. Abstract copy should be sent to the editor in time to ap- 
pear in the JOURNAL issued prior to the meeting. 

Galley proof of abstracts should also be read to pick up printing 
errors, especially with regard to names of authors and their company 
affiliations. Extra sets of galleys of the abstracts should be supplied 
the Chairman of the Publicity Committee for the use of the trade 
publications. These should not be released, however, until publica- 
tion has been made in the JOURNAL. Arrangements for these details 
can be made with the Editorial Office. 

(5) Preparation of Preliminary Program. The preparation of the 
program requires a careful study of the abstract of each paper before 
a suitable arrangement can be made of the papers under various 
special headings. These "sessions" or "symposiums" have proved 
an effective and popular scheme for concentrating the interest and 
stimulating discussion at our semi-annual meetings. It is recom- 
mended that this plan be continued. 

The arrangement of the papers should also be planned with regard 
to the work of the Publicity Committee. For example, papers of 
news value should preferably be scheduled on the first and second 
days of the meeting and distributed to bring at least one such paper 
in each morning and afternoon session. 

When meetings are held in the East, it is recommended that the 
technical paper sessions be restricted to the daytime and held in the 
evening only if the subject matter is very outstanding and is accom- 
panied by a demonstration. Examples of such evening sessions are: 
The paper on "Color Photography" by C. E. K. Mees at the Rochester 
meeting, October- 12, 1936; the "Television Demonstration" by the 
Radio Corporation of America at the New York meeting, October 14, 
1937; and the paper on "The Transmission of Motion Pictures over 
a Coaxial Cable" by H. E. Ives at the Washington meeting, April 25, 

When the meetings are held on the West Coast, however, evening 


sessions should be planned because many of the technical workers in 
the studios find it difficult to get away from production during the day 
but can attend an evening session. Studio visits or open mornings 
should be arranged to permit members from the East to see actual 
production conditions. 

It is recommended that an approximate time allotment be given 
each paper on the preliminary program so the author will know the 
time that has been allowed for his presentation and the discussion of 

The preliminary program copy should be sent in to the editor suffi- 
ciently in advance of the meeting to permit correction of proof and 
mailing of the program at least three weeks before ike meeting, 

(6) Mail Preliminary Program to Each Author. A copy of the pre- 
liminary program accompanied by a letter should be mailed to every 
author. This letter should urge the author to condense his paper and 
rehearse its presentation to keep within the time limits specified. 
It should repeat the request for two copies of the manuscript by a 
specified date. A sample letter is appended to this report. A colored 
paper stock helps to insure that the recipient reads the letter. 

(7) Check All Manuscripts. Every manuscript should be examined 
as received to determine whether (1) two copies have been sent in; 
(2) all figures are included; and (3) whether drawings and graphs 
have been prepared according to regulations, etc. If some of these 
requirements have not been met, the author should be infoimed at 

Authors who have failed to send their manuscripts in by the final 
date specified for receipt of manuscripts should be informed by letter 
that the Papers Committee desire the manuscript at the earliest con- 
venience of the author. Papers arriving late may, at the discretion 
of the Committee, be scheduled on the final program to be read by 
title or substituted for other papers in the event of cancellations. 

It should also be pointed out to authors that although two com- 
plete copies of their manuscript are desired, it is agreeable to supply 
preliminary copies requiring further slight alterations in text or com- 
pletion of illustrations before final release. Such changes should be 
made within two weeks after the meeting. 

(8) Preparation of Final Program. Copy for the final program 
should be prepared about one week before the meeting. The time 
for delivery of each paper should be printed along the left margin. 
This plan has several advantages, namely, (1) the author is informed 


of his starting time and total time for delivery and discussion; (2) 
those members and guests attending the meeting know approxi- 
mately which paper is being read at any given time ; and (3} the chair- 
man of the meeting has the time schedule as a guide. Whenever 
possible the arrangement of the papers on the final program should 
not be changed from that of the preliminary program. Cancellations 
or the offer of a paper on a very timely subject may make a rearrange- 
ment necessary. 

In general, papers whose authors will not be present should usually be 
placed on the last afternoon or at the end of the session on other days. 
Such papers should be marked with asterisks with the explanation 
printed that papers so marked will be restricted to ten minutes for 
presentation, or may be requested to be read by title if the time is 
greatly limited. A request should be made of the author that he 
assign someone to give a digest of his paper and inform the Papers 
Committee several days before the meeting. 

Apparatus papers and manufacturers' announcements of new prod- 
ucts should generally be restricted to ten minutes for presentation. 

The proof of the final program should be checked by the Chairman 
on Saturday morning before the Convention opens on Monday. A 
request should be made for sufficient copies to be delivered Saturday 
afternoon or evening so that they may be distributed to the Board 
of Governors the next day and to the Publicity Committee. 

(9) Final Check- Up at Meeting. It is important that the Chairman 
of the Papers Committee get in touch with every author and any 
other individuals who have been assigned to read papers in the absence 
of the authors, to determine whether all their arrangements are com- 
plete and that they are ready to present their paper at and for the 
time specified on the final program. Good showmanship requires that 
every author be ready when called upon in order that each paper will 
be read as scheduled on the program. 

The question of undelivered manuscripts, missing illustrations, 
corrections on manuscripts, and other details should be discussed 
with the author or his designee at the meeting as this is the best op- 
portunity for the Chairman of the Committee to get such information. 

It is also suggested that the question of papers for the next meeting 
of the Society be kept in mind and that suggestions and offers for 
papers be recorded. 

(10) Examination of Manuscripts Preparatory to Submission to the 
Board of Editors. A final check should be made of every manuscript, 


preferably by reading the manuscript before it is turned over to the 
Chairman of the Board of Editors for consideration for acceptance for 
publication. Notation should be made on the manuscript of any 
special requests made by the author relative to publication. 

General Suggestions. The work of the Papers Committee is not an 
easy task because most individuals in this industry, whether in re- 
search, manufacture, production, or exhibition, are so busy with 
their daily problems that they seldom wish to take the time to write 
up the results of their work. The most interesting papers, however, 
are often those dealing with current developments and, if the Papers 
Committee is alert to its responsibilities, such papers can only be 
secured by approaching those individuals who are working in the 
fields in question. It is necessary, therefore, that the members of this 
Committee establish a cordial working relationship with the leaders 
in various centers of activity in the industry. When these leaders 
have suitable material for papers for our Society, they are more 
likely to offer it to us for consideration. These leaders should be cir- 
cularized at intervals as to the possibility of papers by themselves or- 
their staffs. 

It is realized that it is not possible to lay down any set of rules for 
the most satisfactory organization of the work of any Committee 
but it is hoped that the suggestions given herein may prove of some 
value to those individuals who accept the responsibility of chair- 
manship of the Papers Committee in the future. 

Chairman, Papers Committee 


Oct. 31-Nov. 2, 1938 Detroit, Michigan. 

Please fill in and return at once to Chairman, Papers Com- 
mittee, SMPE, Kodak Park, Rochester, N. Y. 

1. Title of Paper 

(Give exact wording) 

2. Author (s) Name (s) 

(Give initials) 

3. Company Affiliation and Address 


4. Abstract. A complete abstract (about 200 words) is required by Sept. 15th 
for publication in the October number of the Journal. 

5. Manuscript. It is requested that the complete manuscript be sent in to the 
chairman of the Papers Committee not later than Sept. 15th if preferred listing 
on the program is desired. Two copies of each manuscript must be received by October 
1st or the paper may be listed to be read by title on the final program. 

6. Do you expect to present the paper in person? Yes No 

If not, who will present the paper? 

(Time will be restricted if author (s) not present) 

7. Time required for presentation Minutes 

(Usually 15-20 Min.) 

8. Do you expect to show lantern slides? Yes No 

(Facilities will be provided) 

9. Do you plan to show films with your papers? Yes No 

Are they sound or silent ? Length? 35 mm.? 

(Ft.) 16mm.? 

10. Special Requirements. State in detail any special requirements as to dem- 
onstrations, electrical power supply, projection, etc. Facilities will be provided 
for the projection of lantern slides, 16-mm. and 35-mm. motion picture films. 

Rulings on Publicity on Papers and Acceptance of Papers for Publication. 

(1) Acceptance of papers by the Papers Committee does not imply agreement to 
publish. The Board of Editors reserve the right to decline to publish even though 
the paper may have been presented at the convention, unless the manuscript is 
received and accepted one month before the convention. 

(2) Publicity incident to the presentation of papers at conventions is the re- 
sponsibility solely of the Papers and Publicity Committees of the Society and 
should not be undertaken by the authors or their representatives. 

(3) For further details on rules for papers, see the reprint Regulations of the 
SMPE Related to the Preparation of Papers for Presentation and Publication. 




Name and Address of Author 

Dear Mr 

A preliminary program for the (Place) meeting is enclosed for your informa- 
tion. Please note the date and time specified for your paper. It is requested that 
you condense your paper for presentation at the meeting and time it carefully to 


fit in with the specified time requirements. This can be done only by actual re- 
hearsal. Papers for the Apparatus Symposium will be restricted to 10 minutes 
for presentation. 

Papers must be given on the dates specified, unless a change is approved by 
motion of the convention delegates at the proposal of the chairman. 

Papers designated with an asterisk (*) will, in the absence of the author (s) 
generally be restricted to 10 minutes for presentation or may be requested to be 
read by title, if the time is greatly limited. 

The full manuscript should be submitted for publication but is subject to 
final approval by the Board of Editors. Please check over your manuscript 
carefully and see that it conforms with the regulations governing papers. 

Two copies of your manuscript must be in my hands by (Date) in order that 
he paper be listed on the final program. 

Yours cordially, 

Chairman, Papers Committee 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, N. Y. Micro copies of articles, in maga- 
zines that are available may be obtained from the Bibliofilm Service, Department of 
Agriculture, Washington, D. C. 

Educational Screen 

17 (Nov., 1938), No. 9 
Motion Pictures Not for Theaters III (pp. 291-294). 


11 (Nov., 1938), No. 11 
Television Synchronization (pp. 18-20) 

An Automatic Remote Amplifier (p. 21). 
Selecting Loud Speakers for Special Operating Condi- 
tions (pp. 22-24). 
Light and Sound (p. 25). 

A Laboratory Television Receiver V (pp. 26-29). 
Advanced Disc Recording (pp. 34-36, 82). 
International Photographer 

10 (Nov., 1938), No. 10 
New Stereoscopic Method (pp. 10-11). 
Projection Symposium (pp. 24-27). 
International Projectionist 

13 (Nov., 1938), No. 11 

Advance Preparations Minimize Sound System Emer- 
gencies (pp. 7-10). 
Mechanics of Motion Picture Projection (pp. 10-11, 


Theater Structure, Screen Light and Revised Projection 
Room Plans (pp. 12-15). 

Kinematograph Weekly 

261 (Nov. 3, 1938), No. 1646 
Sound-Tracks on Ozaphane Film Stock (p. 29). 
Motion Picture Herald, Better Theatres 

133 (Nov. 12, 1938), No. 7 

Lighting the Theater Interior with the New Fluorescent 
Lamps (pp. 17-19, 25-26). 







Report of the SMPE 
Projection Practice 





Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice-President 

W. C. KUNZMANN. Convention Vice-F 'resident 

J.I. CRABTREE, Editorial V ice-President 

L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 

J. HABER, Chairman, Publicity Committee 

Pacific Coast Papers Committee 

L. A. AICHOLTZ, Chairman 





Reception and Local Arrangements 

H. G. TASKER, Chairman 







Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation 

G. A. CHAMBERS, Chairman 






Convention Projection 

H. GRIFFIN, Chairman 






Officers and Members of Los Angeles Projectionists Local No. 150 

Banquet and Dance 

N. LEVINSON, Chairman 






Ladies 9 Reception Committee 

MRS. N. LEVINSON, Hostess 

assisted by 







J. HABER, Chairman 



New Equipment Exhibit 

J. G. FRAYNE, Chairman 



O. F. NEV 


Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Special hotel rates, guaranteed to SMPE delegates, European plan, will be as 
follows : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8 . 00 

Parlor suite and bath, 2 persons 12.00 

228 1939 SPRING CONVENTION fj. s. M. P. E. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available 
to those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately 
upon arriving at the Hotel. Convention badges and identification cards will 
be supplied which will be required for admittance to the various sessions, the 
studios, and several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges : 


Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 147.50 23.65 

Detroit 106.75 19.20 

New York 139.75 22.85 

Rochester 124.05 20.50 

Cleveland 110.00 19.20 

Philadelphia 135.50 22.35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips, sixty-day limits. Arrange- 
ments may be made with the railroads to take different routes going and coming, 
if so desired, but once the choice is made it must be adhered to, as changes in the 
itinerary may be effected only with considerable difficulty and formality. Dele- 
gates should consult their local passenger agents as to schedules, rates, and stop- 
over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems, and 
arrangements will be made to visit several of the studios. The Local Papers 
Committee under the chairmanship of Mr. L. A. Aicholtz is collaborating closely 
with the General Papers Committee in arranging the details of the program. 
Complete details of the program will be published in a later issue of the JOURNAL. 

Semi- Annual Banquet and Dance 

The Semi- Annual Banquet of the Society will be held at the Hotel on Thursday, 
April 20th. Addresses will be delivered by prominent members of the industry, 
followed by dancing and entertainment. Tables reserved for 8, 10, or 12 persons; 
tickets obtainable at the registration desk. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the general office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Feb., 1939] 1939 SPRING CONVENTION 229 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Inspection Tours and Diversions 

Arrangements are under way to visit one or more of the prominent Hollywood 
studios, and passes will be available to registered members to several Hollywood 
motion picture theaters. Arrangements may be made for golfing and for special 
trips to points of interest in and about Hollywood. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. N. Levinson, hostess, and the Ladies' Committee. A 
suite will be provided in the Hotel, where the ladies will register and meet for 
the various events upon their program. Further details will be published in a 
succeeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Li- 
brary and Art Gallery (by appointment only); Palm Springs, Calif.; Beaches at 
Ocean Park and Venice, Calif.; famous old Spanish missions; Los Angeles Mu- 
seum (housing the SMPE motion picture exhibit); Mexican village and street, 
Los Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, 
and Palm Springs, and special tours may be made throughout the Hollywood 
area, visiting the motion picture and radio studios. 

On February 18, 1939, the Golden Gate International Exposition will open 
at San Francisco, an overnight trip from Hollywood. The Exposition will last 
throughout the summer so that opportunity will be afforded the eastern members 
to take in this attraction on their convention trip. 



As a result of recent elections, announced at the meeting of the Section on 
January llth, the following members constitute the Board of Managers for 1939: 

*D. E. HYNDMAN, Chairman 

G. FRIEDL, JR., Past-Chairman **H. GRIFFIN, Manager 

*P. J. LARSEN, Sec.-Treas. *R. O. STROCK, Manager 

*Term expires December 31, 1939 
**Term expires December 31, 1940 

The meeting of January llth was held at the Hotel Pennsylvania, New York, 
N. Y., and was devoted to a celebration of the centenary of the announcement to 
the French Academy of Sciences in January, 1839, by Arago, of the contributions 
of Daguerre to the art of photography. Two papers were presented as follows: 

"The Early History of Photography," by Edward Epstean. 
"Daguerre's Contribution to Photography," by Beaumont Newhall. 

The joint presentation told the story of how the world was awakened in 1839 to 
the idea of photography and how, as the result of the divulgation of Daguerre's 
method, scientists were stimulated to perfect their independent processes, notably 
John Fox Talbot in England, whose work was concerned with a positive-negative 
process admitting of duplication by printing, whereas Daguerre's was a "one-shot" 

The details of the birth of photography and the early technics were also de- 
scribed, and Mr. Newhall's lecture was illustrated by several lantern-slide copies 
of original Daguerreotypes. The meeting was well attended and considerable 
interest was shown in the presentations. 


As outlined in the preceding section of this issue, and also as announced on the 
inside front cover, the next convention of the Society will be held on April 17th- 
21st, inclusive, at Hollywood, Calif., with headquarters at the Hollywood Roose- 
velt Hotel. 




Balance, Dec. 31, 1937 
Receipts during 1938 
Membership dues 
Sustaining Membership 
Publication (Journal sales, reprints, 

subscriptions, advertising, etc.} 
Other income (membership certifi- 
cates, Journal binders, test-films, 
interest, etc.} 


Disbursements during 1938 

Publication (Journal, reprints, bind- 
ers, etc.} 

Office expenses, rent, and salaries 

Officers' expenses 

Local Sections 

Other expenses (dues and fees, test- 
films, misc.) 














Balance, December 31, 1938 

$24,223. J 
L. W. DAVEE, Treasurer 



Prior to January, 1930, the Transactions of the Society were published quar- 
terly. A limited number of these Transactions are still available and will be 
sold at the prices listed below. Those who wish to avail themselves of the op- 
portunity of acquiring these back numbers should do so quickly, as the supply 
will soon be exhausted, especially of the earlier numbers. It will be impossible 
to secure them later on as they will not be reprinted. 






















Beginning with the January, 1930, issue, the JOURNAL of the Society has been 
issued monthly, in two volumes per year, of six issues each. Back numbers of 
all issues are available at the price of $1.00 each, a complete yearly issue totalling 
$12.00. Single copies of the current issue may be obtained for $1.00 each. 
Orders for back numbers of Transactions and JOURNALS should be placed through 
the General Office of the Society and should be accompanied by check or 


The following are available from the General Office of the Society, at the prices 
noted. Orders should be accompanied by remittances. 

Aims and Accomplishments. An index of the Transactions from October, 
1916, to December, 1929, containing summaries of all articles, and author and 
classified indexes. One dollar each. 

Journal Index. An index of the JOURNAL from January, 1930, to December, 
1935, containing author and classified indexes. One dollar each. 

SMPE Standards. The revised edition of the SMPE Standards and Recom- 
mended Practice was published in the March, 1938, issue of the JOURNAL, copies 
of which may be obtained for one dollar each. 

Membership Certificates. Engrossed, for framing, containing member's name, 
grade of membership, and date of admission. One dollar each. 

Lapel Buttons. The insignia of the Society, gold filled, with safety screw back. 
One dollar each. 

Journal Binders. Black fabrikoid binders, lettered in gold, holding a year's 
issue of the JOURNAL. Two dollars each. Member's name and the volume 
number lettered in gold upon the backbone at an additional charge of fifty cents 

Test- Films. See advertisement in this issue of the JOURNAL. 




Volume XXXII March, 1939 



Latest Developments in Variable- Area Processing 


Improving the Fidelity of Disk Records for Direct Playback . . 


The Centenary of Photography and the Motion Picture 


The Surface of the Nearest Star R. R. McMATH 264 

The Electrical Production of Musical Tones S. T. FISHER 280 

A Color-Temperature Meter 


Chemical Analysis of an MQ Developer 


An Opacimeter Used in Chemical Analysis 


A New Projector Mechanism H. GRIFFIN 325 

1939 Spring Convention at Hollywood, Calif 336 

Society Announcements 341 

Constitution and By-Laws of the Society 344 





Board of Editors 
J. I. CRABTREE, Chairman 




Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 


** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 
** Past-President: S. K. WOLF, RKO Building, New York, N. Y. 
** Executive Vice-P resident: N. Levinson, Burbank, Calif. 

* Engineering Vice-P resident: L. A. JONES, Kodak Park, Rochester, N. Y. 
** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 
** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 

* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. J. 

** M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

* H. GRIFFIN, 90 Gold St., New York, N. Y. 

* D. E. HYNDMAN, 350 Madison Ave., New York, N. Y. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

* A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 

** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys Calif. 

* Term expires December 31, 1939. 
** Term expires December 31, 1940. 



Summary. The purpose of this paper is to present a series of curves showing the 
photographic control oj variable-area sound-tracks in commercial production at 
Warner Bros. Studio, and to show the wide tolerances in film processing permissible 
with Class A push-pull recording, a factor that is of especial interest in daily produc- 

The results of a study of the technic involved in fine-grain photographic duplicating 
of variable-area sound-track, for foreign release are also discussed. 

The photographic control of variable-area sound-tracks in com- 
mercial laboratories has been satisfactorily established by the use of 
modulated high-frequency test recordings. The nature of these tests 
has been previously described by Baker and Robinson r 1 

The quality of variable-width sound records depends to a great extent upon 
image definition. The requirements for a perfect sound-track are complete 
transparency in the clear portion, complete opacity in the dark portions, an 
extremely sharp boundary between the clear and dark portions, and exact dupli- 
cation of the wave traced upon the track by the galvanometer. 

Distortion is introduced by any change in average transmission in recording 
high-frequency waves. At high densities the average transmission is reduced, 
and at very low densities is increased by the presence of the high-frequency waves. 
The average transmission is compared to the transmission through the film for a 
50-per cent exposed track without signal. 

It is possible to find a density at which there is little, if any, change in average 
transmission, and this density corresponds to most nearly perfect image defini- 
tion and least distortion .... 

A modulated high-frequency recording affords an extremely accurate means of 
determining correct negative and print densities for given conditions of labora- 
tory processing. An oscillator, designed for several carrier frequencies, is pro- 
vided with a 400-cycle modulator for recording. The modulated carrier is 
recorded for several values or lamp current, and processed to several negative 
densities. Prints are then proceeded to various values of density, and the 400- 

*Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 
10, 1938. 

**RCA Manufacturing Co., Hollywood, Calif. 
fWarner Bros Pictures, Inc., Burbank, Calif. 




[J. S. M. P. E. 


J: f 

: * H 

I -8 

Q- hfi 

I .fH 


oij.v-\oaow SSOSD do 



FIG. 1. Cancellation curves for standard bi- 
iteral and Class A push-pull tracks, plotted 
gainst negative density. 



"a. \^ 











, * 







? ? ? a a s is ? 


cycle output measured on suitable reproducing equipment. The combination of 
negative and print densities that gives least 400-cycle output indicates the con- 
dition for best image definition and least distortion .... 

This method of test was used to determine the data presented in 
this paper. 

In the daily production of sound-tracks, certain variations in track 
density are always present. These variations are due to a number 
of causes, such as emulsion speed, exposure, development, retrogres- 
sion, temperature, etc. While these variations may be held to a 
minimum, they become apparent when the final film is assembled for 
re-recording. Such variations require accurate measurement of track 
density, the use of a card-index system for indexing the densities of 
the several hundred scenes of each production, and the timing of the 
cut negative when prints for re-recording purposes are made. This 
procedure involves clerical expense, extra handling of the negative, 
and a considerable loss of time in preparing the re-recording prints. 

Such variations are practically eliminated by the use of Class A 
push-pull for the original daily production. The advantage of the 
Class A track is primarily due to cancellation of even-harmonic dis- 
tortions which may arise from daily variations in the process. Thus 
the daily track, recorded push-pull, provides a higher average and 
more uniform quality than the standard track. Accurate timing of 
the negative is unnecessary when making the print for re-recording, 
as variations in negative density within reasonable limits produce so 
little change in the relative level of cross-modulation products that 
they can be disregarded. 

Fig. 1 shows the comparative cancellation curves for standard 
bilateral and Class A push-pull tracks plotted against negative den- 
sity. These data are established by frequency tests consisting of (1) 
1000 cycles for reference level, (2) modulated 9000 cycles for distor- 
tion test. It has been found by practical experience that a cancella- 
tion of 30 db. is satisfactory for all types of material; therefore den- 
sity tolerances may be established at this value of cancellation. Thus 
from Fig. 1 the negative density tolerance for the standard track 
at a print density of 1.59 is from 1.93 to 2.10, while for the push-pull 
track the density latitude is almost unlimited. It can be readily seen 
from this that variations in negative density present in the daily pro- 
duction become relatively unimportant when using the push-pull 
system, and that only very erratic conditions would necessitate special 
timing of the negative. 

240 A. C. BLANEY AND G. M. BEST [j. s. M. p. E. 

Fig. 2 shows the same comparison, plotted against print density. 
Here the optimum negative density as indicated in Fig. 1 is made into 
a loop and printed to a number of densities within the range of the 
printer. Again the latitude in print density for the standard track 
is somewhat limited, being within the range of 1.53 to 1.70, whereas 
the push-pull is almost unlimited. While the latitude of the standard 
track is sufficiently broad to cover variations in the re-recorded nega- 
tive and release printing, the use of push-pull tremendously simplifies 
the daily production routine. 

Due to theater limitations, it is necessary to make all re-recorded 
tracks standard for release. However, since the re-recording is ac- 
complished in a comparatively short period of time, is done in large 
sections, and is subject to better control than the daily production, 
the variations are much less. The density tolerances on the 
standard track are sufficiently wide to accommodate all normal 
variations that exist during the re-recording process. 

Photographic Dupes. Most producing companies retain the original 
sound-track and picture negatives in the United States, preferring to 
send photographic dupes to the foreign market rather than risk having 
the original negative cut by censors or damaged in transit. For eco- 
nomic reasons, most photographic dupes for foreign release are made 
with the picture and sound-track on the same film. Since consider- 
able emphasis has been placed on the necessity, of having a gamma 
of 2.00 or over for variable-area tracks, there has been much skep- 
ticism as to the possibility of making high-quality composite dupes 
by following the picture process, which requires the use of relatively 
low gammas. It must be pointed out that high gamma is necessary 
only when it must be used as a means to increase sharpness; if the 
emulsion and development produce the necessary contrast and sharp- 
ness, the actual gamma is unimportant. 

With fine-grain duplicating positive and negative emulsions of 
great resolving power now available, experiments were first carried 
out in the RCA engineering laboratory at Camden to determine what 
degree of sound quality could be reproduced in a composite photo- 
graphic dupe. Frequency measurements indicated the losses to be 
very small, and duplicate prints of speech and music compared very 
favorably with prints from the original negative. Production work 
at the Warner Hollywood laboratory proved conclusively the satis- 
factory operation of the process. All data for this paper were taken 
from production work at the Warner Bros, laboratory. 


Since the picture specifications control the development character- 
istic of each step of the duplicating process, there is left only the 
quality and intensity of the printing light to be controlled in printing 
the track. 

The frequency negative for the duplicating tests is made on the 
same recorder and at the same time as the re-recorded negative, so 
that it will exactly represent the conditions of the release negative. 
This negative is also used for control of the domestic release prints. 

Fig. 3 shows the cancellation curve for the Eastman fine-grain du- 
plicating positive stock type 1365 developed to a gamma of 1.26 in 
D-76 developer, printed from the release negative test having a dens- 
ity of 2.05. This print is exposed with white light because there is 
very little sharpness to be gained by using filtered light on this emul- 
sion. It is seen that the greatest cancellation occurs at a positive 
density of 1.45, which, if the print was to be used for theater reproduc- 
tion, would be the correct print density. However, it is not desirable 
to use this print density for making the duplicate negative. Due to 
picture specifications, the dupe negative is developed to a low gamma 
and will thus have a comparatively large amount of image spread. 
Therefore, to cancel some of this, it is desirable to use a master 
positive having image spread in the opposite direction. A density of 
1.9 on the type 1365 fine-grain positive has considerable image spread 
and is about the highest density contrast that can be obtained on the 
track at this gamma, so a print density of this value is used for the 
master positive. 

Fig. 4 is the cancellation curve of the dupe negative printed from 
the 1.9-derisity master. The stock used is the Eastman fine-grain 
duplicating negative type 1203 developed in D-76 developer to a 
gamma of 0.58. This stock is panchromatic in its sensitivity, and 
considerable gain in sharpness can be obtained by the use of a filter. 
A Corning No. 556 filter 5 mm. thick restricts the actinic light to 
wavelengths shorter than 5000 A and procures most of the possible 
advantage. Also, the total amount of light required for printing this 
stock with the filter is no more than is required for the type 1365 stock. 

The curve shows that the maximum cancellation occurs at the 
same density as the maximum density contrast; therefore a density 
of 1.33 is indicated for making the final prints. However, it has been 
found from experience with a number of pictures put through the 
duping process, that it is advisable to work within a density range on 
the dark side of the indicated maximum cancellation point, so that 



[J. S. M. P. E. 

t.o I.I I.Z I.S 1.4 1-5 > 1-7 

FIG. 4. Cancellation curve of dupe negative 
printed from the 1.9-density master: fine-grain 
duplicating negative type 1203, D-76 developer, 
gamma 0.58. 

NI Cl^X'Bd 



r * 3 s*5 







-- -^ 


, T7r7?rr ^. 

a a NI sa.:>oaoa<i Noirvioaow SSOSD jo naA'ai aAu.vra* 


I.I 1.2. i.5 14 i.S 1.6 1.7 1.6 )<* z. 

M*ftR. PoeiTWt OtKlSlTV 

FIG. 3. Cancellation curve of EK fine-grain 
duplicating positive stock type 1365 (gamma 1.26, 
D-76 developer), release negative test density 2.05. 










- > 




Dtnoin in o in o io 

i 77 y 1 jj*>*>^->- 

a a NI siooaottd Noii.vif\aow csoaa ^o TIAIT -jAu>n 

Mar., 1939] 



in commercial practice this range is from 1.33 to 1.40. Negatives that 
are below the 1.33 optimum density quickly become excessively sibi- 
lant, and those that are kept within the range from 1.33 to 1.40 suffer 
no impairment of frequency characteristic and no sibilants are intro- 
duced in excess of those already existent in the recording. 

Fig. 5 shows the cancellation curve for the positive type 1301 
prints made from the dupe negative. These prints are made accord- 









I.O I.I l.Z 1.3 1.4 IS 


FIG. 5. Cancellation curve for positive type prints 
made from the dupe negative. 

ing to the standard release practice restricting the exposing light to a 
wavelength shorter than 4000 A by a Corning 584 filter and developed 
to a gamma of 2.28. The maximum cancellation value as indicated 
by the curve at a track density of 1.35 is used for the final prints from 
the duplicate negative. The curve also indicates a possible 0.1 
density variation without serious effect. 

Frequency response tests indicate an overall level loss of 1 db. due 
to the printed-in fog on the dupe prints, and an attenuation at 7000 
cycles of 1 db., as compared with an original print. 

244 A. C. BLANEY AND G. M. BEST [j. s. M. P. E. 

The sound quality that can be obtained in a print is largely depend- 
ent upon the performance of the printer. Slippage must either be 
eliminated or reduced to a minimum and held constant. And, most 
important of all, the films must be maintained in absolute contact. 
The benefit of these factors can be appreciated only by experiencing 
the results produced by such a printer. 

It is advisable to carry the frequency test through the duping proc- 
ess along with the production material. This test becomes useful in 
two ways : first, it is a check on the duping process, and second, the 
test dupe negative is sent to the foreign laboratory so that the proper 
printing conditions may be established for that particular production. 

A number of pictures have been satisfactorily duped by this process 
at the Warner Hollywood laboratory. It is their practice to make 
one master positive from which two dupe negatives are made. All 
these films are exported to foreign markets. However, in order to 
check the process a complete composite release print is made from 
each dupe negative. As evidence of the quality obtained, these prints 
compare so favorable with those made direct from the original nega- 
tive that they are used in the domestic release. 


1 BAKER, J. O., AND ROBINSON, D. H.: "Modulated High-Frequency Record- 
ing as a Means of Determining Conditions for Optimal Processing," /. Soc. Mot. 
PicL Eng., XXX (Jan., 1938), p. 3. 


MR. ROBERTS: Why in all these curves did the authors obtain optima on both 
negative and positive processes? It is my understanding of cross-modulation 
theory that a certain fill occurs in the negative process, and then a certain amount 
of fill of the opposite kind in the positive process, which causes a dip in the curve 
forming an optimum position which we try to print. 

In this process the authors apparently get an optimum on 1365 positive film. 
One would expect that, because the fill of the negative is being cancelled. Now, 
they pick a point above the optimum, where the cancellation is greater than is 
needed. Therefore, one would expect that the negative on 1203 film would give 
an optimum; but the authors apparently pick the optimum point on the 1203 
negative curve and make their prints from that. 

It would seem to me that one would be finished once he had picked an optimum 
for the negative, and not expect an optimum on the final 1301 print, but just get a 
sort of rising curve. 

MR. WOLFE: No matter what the image-spread may be on the negative with 
which we start, there is an optimum print from that negative. It may not always 
be the same. We do normally try to select the density of the original negative at a 


point that will bring the cancellation at a desired density on the print, but if we 
use a different negative density there would still be an optimum print density, but 
not at the same point. 

MR. ROBERTS: In using a negative and print we have a combination. In 
general, we get optima on, say, print processes, but why is it you get optima in both 
negative and positive? I regard the negative and positive as a unit, and we get a 
family of curves for every negative and positive. But if we plotted the cross- 
modulation products of the original negative, as it is taken from the developing 
machine, we would not get a minimum. Why, then, should we get a minimum in 
a duplicate negative process? 

MR. WOLFE: If you take a negative and vary the exposure you will get a 
minimum. We sometimes make use of that fact when we wish to play the nega- 
tive. For example, if we know in advance that a particular piece of film is being 
made for play-back purposes only, it will not be printed, and it is exposed differ- 
ently from the way in which it would be exposed if we expected to print it ; so the 
variable is exposure on the negative. Again I think the point is quite definite, 
that there is a minimum in every case, and where that minimum occurs depends 
entirely upon the preceding process. 

MR. ROBERTS : I had the idea that in one process we got only one sort of effect ; 
that is, in the negative we have only the fill of the valley; and in the print we fill 
the valley corresponding to the peak of the negative, so as to equalize and make 
the sound-wave symmetrical. 

MR. WOLFE: What we are talking about here is image-spread, and it must be 
clear that in every photographic process there is an exposure and a development 
condition that results in a minimum amount of image-spread. It so happens that 
for the normal practical process we expose and develop the negative in a manner 
that does not give the negative minimum image-spread. 

That is done in order that the image-spread may be used to cancel the image- 
spread of the print that results when the print is at a density value desirable from 
the standpoint of the level of sound reproduced. 



Summary. Recent advances in design, and in materals of which the recording 
disks are composed, have resulted in improved fidelity. Both the volume range ob- 
tainable, and the frequency range, have been extended, satisfying present-day require- 
ments of motion picture and broadcast applications. 

For reproduction, there is provided a new light-weight lateral pick-up having high 
sensitivity and equipped with a permanent diamond point. This reproducer, in 
combination with its associated circuit, is suitable for use on all lateral cut disk 

Pre- and post-equalization are employed in making high-fidelity records, insuring 
a low noise level. This reduction of background noise together with the wide frequency 
range and low distortion create an illusion of realism or "presence" during reproduc- 

Usually a large number of playings is not required from direct playback disks. 
However, because of the low mechanical impedance of the new RCA pick-up and the 
improved composition of the disks, it is possible to reproduce many times without 
appreciable increase in noise or distortion. 

Constant demand for better direct playback recordings has resulted 
in the development of equipment and disks of improved quality. 
These advances have opened new fields and today the applications 
for direct playback recording are numerous. 

The art has advanced well past an experimental state and is now 
used on a production scale for sound motion pictures, radio broad- 
casting, schools, industrial advertising, musical education, auditions, 
government activities, and aviation. 

RCA has developed direct playback equipment having improved 
performance characteristics. A typical studio installation is shown 
in Fig. 1. Here may be seen the feed-screw mechanism with record- 
ing head and the new light-weight lateral reproducer. 

Lateral or "push-pull" modulation was adopted because of its low 
distortion characteristics. A frequency range of 50 to 10,000 cps. is 

*Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 24, 

**RCA Manufacturing Co., Camden, N. J. 




covered with reasonable uniformity. A volume range of approxi- 
mately 55 db. is obtainable using the frequency range specified. The 
records have sufficient life for most purposes and when protected 
from dust, finger prints, and oxidation may be played seventy-five 

FIG. 1. 

Recording and reproducing system for broadcast 
studio use. 

or more times using the light-weight flexible pick-up shown. Usually 
a large number of playings is not required and no special care in han- 
dling the disks is ordinarily demanded. 

The MI 4887 recording head consists of a mechanical band-pass 
network terminated by a special mechanical resistance material. The 


III 4 

ft o u o (j 


















FIG. 2. Frequency response recorder head (MI-4887} optical measurement, 
lateral stylus velocity. 

impedance of the moving system is such that the motion of the cutting 
stylus is practically unaffected by the impedance of the record com- 
position. This permits a free-space microscopic measurement of 
the performance of the head, which is duplicated almost exactly when 
cutting a record. The frequency response characteristics of two types 



[J. S. M. p. E. 

of recorder heads are shown in Fig. 2. It will be seen that frequen- 
cies below 800 cps. are controlled so as to hold the amplitudes about 
constant, the stylus velocity diminishing as the frequency is reduced. 

FIG. 3. Construction] of recording cutter and equivalent 
electrical circuit. 

This practice is followed generally in disk recording to avoid cutting 
through to adjacent grooves at low frequencies. The loss is made by 
suitable compensation in the reproducing circuit. 

The construction of the recording cutter and the equivalent elec- 
trical circuit are shown in Fig. 
3. Since for constant current 
in the recorder winding, the 
armature receives a constant 
force, the electrical circuit is 
shown working from a con- 
stant-voltage source. The out- 
put of the mechanical system 
is represented by the lateral 
stylus velocity and is equiva- 
lent to current through the 
second inductance of the elec- 
trical network. This circuit has 
















FIG. 4. Total distortion (rms.) to be 
expected at 400 cps. 

a rising characteristic with increasing frequency, compensating for 
diminishing current through the recorder winding due to inductance. 
The merits of lateral recording have been discussed at length. Of 
chief importance is the cancellation of even harmonic distortion. 1 

Mar., 1939] 



Under normal operating conditions, the overall distortion of the 
combined recording and playback operations is less than 5 percent. 
The rms. total distortion to be expected at 400 cps. at varying de- 
grees of modulation is indicated in Fig. 4. These observations were 
made at a record speed of 33.3 rpm. and a diameter of 12 inches. 

15 14 13 12 II 10 9 8 


FIG. 5. Average losses at various record diameters at 
33.3 rpm. 

All disk systems suffer from high-frequency transfer losses and in- 
creased distortion when the record diameter or linear surface speed 
becomes too small. The average losses encountered at various record 
diameters at 33.3 rpm. are shown in Fig. 5. These are for soft com- 
position blanks used in direct playback work. The losses are less 
serious on standard records pressed from harder material. 

</) Ul 


a z-15 



5000 10,000 

FIG. 6. 

500 1000 

Reproducer characteristic with standard 12-inch pressing at 33.3 rpm. 

These losses are caused by a combination of the finite size of the 
reproducing point, the wavelength of the recorded sound, the weight 
of the pick-up, and the compliance of the record stock. It is possible 
to compensate to some extent for the losses but it has not been found 
practicable to attempt full compensation above 6000 to 7000 cps. 
because of the serious attenuation in the upper register. Therefore, 
in making high-fidelity records where quality is of paramount im- 
portance, the best results are obtained by dividing the time into two 
or more disks and confining the recording to reasonably high linear 



[J. S. M. P. E. 

Some reduction in transfer loss can be effected by departing from 
standard groove dimensions, for example, by reducing the radius 
from 0.0023 inch to 0.001 inch. A further reduction could be made by 
increasing average record speed. In view of the extensive duplication 
of equipment neither solution appears to be economical. 

The MI-4856 reproducer is intended primarily for use on non- 
abrasive high-fidelity records but may be used on all lateral records 
having standard groove dimensions, including composition coated 
disks used for immediate playback. It is equipped with a permanent 
diamond point, the radius of which corresponds to the 0.0023-inch 
standard. This radius is held to limits not exceeding plus or minus 
0.0001 inch to insure an even distribution of pressure over the bottom 
of a standard groove. 

The frequency response characteristic of the reproducer from a 
standard test pressing twelve inches in diameter and running at 33.3 


50 IOO 500 1000 5000 10,000 

FIG. 7. Recording and reproducing amplifier charcteristics. 

rpm. is shown in Fig. 6. The internal construction of the pick-up is 
shown schematically in Fig. 8. The armature is of the clamped reed 
type. The two upper air-gaps are inactive, being filled by non- 
magnetic spacers. Since the armature impedance is too high to be 
directly coupled to the record a linkage having a 6 to 1 leverage ratio 
or a 36 to 1 impedance ratio, is employed. The diamond point is 
secured in the lower end of an extremely light pivot arm spring 
supported vertically but rigid laterally. Thus, the pivot arm is per- 
mitted to rise, as during "pinching," without lifting the entire pick- 
up. In the direction of useful motion being transmitted to the arma- 
ture, the linkage has a minimum of compliance and the upper cut-off 
is high or about 9000 cps. This peak is reduced by means of a block 
of loaded rubber arranged as a selective damper tuned approximately 
to the peak frequency. 

The response of the pick-up working into a resistance load would 
droop at high frequencies because of the inductance of its winding 

Mar., 1939] 



unless the winding were kept small. This is not consistent with high 
output. Therefore a shunt capacity is connected across the pick-up 
which, by reacting broadly with the inductance, increases the re- 
sponse through a portion of the upper range. The reproducer has a 
slightly rising characteristic at the upper end, enough to offset high- 
frequency needle or transfer losses encountered at a mean record 
diameter of twelve inches at 33.3 rpm. 

In making high-fidelity records, including disks for immediate play- 
back, use is made of what is known as pre- and post-equalization or 
complementary compensation . Because of the energy distribution in 
most speech and music, it is 
possible to accentuate the higher 
frequencies when making a record 
and attenuate them in reproduc- 
tion, thereby reducing the sur- 
face or ground-noise due to the 
record stock. 

Fig. 7 shows the recording and 
reproducing amplifier characteris- 
tics and the ideal overall to which 
must be added the characteris- 
tics of the reproducer. This 
method of reducing surface noise 
can be used successfully in most cases without adding appreciable 

Tests indicate negligible wear of the diamond stylus on non- 
abrasive records. On shellac composition records there is sufficient 
wear after 5000 ten-inch faces to justify replacement of the point. 
This is considerably longer life than so-called permanent points of 
iridium or sapphire, when used on abrasive records with the same 
pressure of two ounces. 

An improvement in pick-up tracking has been made by offsetting 
the head with respect to the arm. This angle, which is about ten 
degrees, results in two positions of tangency with the groove, one near 
the center of the record and the second near the outer edge. The 
error in tracking angle between these positions is less than 5 degrees. 



FIG. 8. Construction of pick-up. 

1 PIERCE, J. A., AND HUNT, F. V.: "Distortion in Sound Reproduction from 
Phonograph Records," /. Soc. Mot. Pict. Eng., XXXI (Aug., 1938), p. 157. 



MR. WOLF : Is this a conventional form of acetate ? 

MR. HASBROUCK: Yes. The response was equalized to 9500 or 10,000 cps. 
There was no limitation below that either in recording or reproduction. 

MR. WOLF: Are any of the studios now making use of it for playback? 

MR. HASBROUCK: Yes, many of them, both motion picture and broadcast 

MR. CARVER: When you say the "conventional type acetate" I suppose you 
mean nitrate. All I have ever seen was nitrate. 

MR. HASBROUCK: That word "acetate" is misused. It is a nitrate base. 
There are other ingredients. 

MR. CRABTREE : What are the merits of this lateral system as against the hill- 

MR. HASBROUCK: That has been discussed at great length in many publica- 
tions. The chief advantage is the cancellation of even-harmonic distortion in the 
lateral system. It is similar to a "push-pull" amplifier. 

MR. JOHNSON: The hill-and-dale controversy is like an automobile running 
over a rough road, compared to an engine on a wavy track. The best contact 
between the needle and the groove will, of course, be in the lateral cut track. 
When the stylus digs deeper the drag is greater, and there is likely to be chattering. 

MR. CRABTREE : Many years ago we had demonstrations at these meetings of 
hill-and-dale records which, to me, were quite pleasing. It is unfortunate that the 
author did not bring along his recorder and actually record in the room and 
reproduce, say, a speech by our President. I wish we could arrange at the next 
meeting for someone to put on such a demonstration. It means so much more 
when we hear the original and then the reproduction, than to hear merely the 

MR. WOLF: Is this system used in Hollywood to the exclusion of other play- 
back methods? Is the Miller system being used at all for immediate playback: 

MR. WOLFE : To the best of my knowledge, the Miller system is not being used 
in the studios, but this method is certainly not the only one in use for playback 

Again, so far as I know, variable-density negative is not being played back in 
the studios, but R.K.O. does play back variable-area negative in certain cases. 
Two methods of playing back are used : either acetate disk, some of it lateral and 
some hill-and-dale, or by reproduction from film. 

MR. WOLF: I think before long electromagnetic recording will probably be in 
the studios. The Bell Laboratory has been working for a number of years on that 
method of recording. I think you will see at the New York World's Fair, if not 
before, a quality of magnetic recording comparable with the best playbacks most 
of us have ever heard. That medium will also be very useful for certain kinds of 
playback and editing. 



January 7, 1939, marked the centenary of the day when Arago communicated to 
the French Academy of Sciences news of the invention by Daguerre of what was to be 
known as the daguerreotype. 

At the suggestion of the Societe Fran$aise de Photographie that ceremonies and meet- 
ings be held by scientific and engineering bodies throughout the world to commemorate 
this Centenary, the Atlantic Coast Section of the SMPE devoted its January, 1939, 
meeting to two presentations: the one that follows, by Edward Epstean, describing 
the historical background of Daguerre' s time, as related to photography, or "light 
writing"] and the second by Beaumont Newhall, describing more in detail the work 
of Daguerre and his process. 

The erroneous popular idea that engineers are mechanics, with no 
interest in the history or philosophy of their profession is, I am sure, 
not held by the members of this Society. I do not hesitate, therefore, 
on this Centenary of the "Discovery of Photography," to address 
you on this subject, tracing the history and progress of the art lead- 
ing to your specialized science of motion picture engineering. 

Motion pictures, as we know them today, were originally called 
"animated photographs" and later "moving pictures." 

Robert Hunt, the English professor of physical science, wrote in 
1854 : "The progress of discovery is ordinarily slow, and it often hap- 
pens that a great fact is allowed to lie dormant for years, or for ages, 
which, when eventually revived, is found to render a fine interpreta- 
tion of some of Nature's harmonious phenomena and to minister to 
the wants or the pleasures of existence. Of this position, Photography 
is peculiarly illustrative." 

The universal application of photography, which ranges from the 
hobby of the amateur on through the wide fields of science and in- 
dustry, might suffice to arouse in any one the desire for a short study 
of its antecedents and its early development. This year is extremely 

*Presented at a meeting of the Atlantic Coast Section, January 11, 1939. 
** New York. N. Y. 


254 E. EPSTEAN [j. s. M. p. E. 

appropriate, because January 7, 1939, marks the Centenary of the 
day when the French scientist, Arago, member of the Chamber of 
Deputies and of the Academy of Sciences, communicated the first 
news of this new discovery to the members of the Academy. After 
a few months of necessary political procedure, the French Govern- 
ment, through Arago, published the details of the process not of 
photography, but of the daguerreotype. 

To give a full history of what today is called photography with its 
background, development, and innumerable applications would re- 
quire many volumes. The word photography, from its derivation, 
implies primarily a study of light, and early in Genesis the word is 
mentioned in its very first verses. Ever since, philosophy and science 
have attempted without success to define and explain Light. Dr. 
Woodbridge, of Columbia University, writes in his chapter on the 
subject that: "it is a paradox" and it probably will remain so, in 
saecula saeculorum. We know little of its action and you will easily 
understand my meaning when I call your attention to the use of the 
phrase: "seeing the sun, the moon, the stars." What we see, of 
course, is only the radiation of their light and not its source. Dis- 
tance, time and space, its brilliancy, and its movement, our imperfect 
optical apparatus all make it impossible to see that essence which 
we include in the term "the light." I have read that stars which have 
been extinct for 400 years still impress our vision with their light. 

Resuming our study of photography we find the camera obscura. 
Some historians have tried to trace its origin to the Arabs. Astrologers 
were attached to the courts of their rulers, whose lives, fortunes, and 
wars were influenced by the astrological studies of the planets, based 
on the day and hour of the ruler's birth. In order to study them 
apart from the myriads of other stars surrounding them, the seers 
built observation huts where no light could enter save through a hole 
in the roof of the "dark room." 

Leonardo da Vinci in his notes on optics states : "... if the front of 
a building . . . which is illuminated by the sun has a dwelling over 
against it, and in that part of the front which does not face the sun 
you make a small round hole, all the objects which are lighted by the 
sun will transmit their images through this hole, and will be visible in- 
side the dwelling on the opposite wall which should be made white. 
And they will be there exactly but inverted; and if in different parts 
of the same wall you make similar holes you will produce the same 
effect in each." And thus we have "light" writing through a so-called 


"pinhole lens" on a white wall or on white paper fastened opposite 
the hole. 

Cameras, front boards, bellows, and plate holders have since been 
constantly improved. From the beginnings of photography the cam- 
era obscura was equipped with a single lens, but soon thereafter came 
the periscopic lens, the meniscus prism, and double objectives. 

Astrologers were displaced, largely through the greed for precious 
metals, by the alchemists, forerunners of the chemist in our special- 
ized field the photochemist. 

Northern Italy, which provided colored ribbons and fabrics for 
Europe during the eighteenth century, was naturally interested in 
the action of dyes and colors, and to Beccarius is ascribed the priority 
of discovery of the light sensitivity of chloride of silver. An earlier 
work, in Latin, by Agricola (1490-1555) deals with silver ores. This 
work was translated into English by President and Mrs. Hoover. 
Here is one of the examples of a comatose condition, because a closer 
study of this work might have hastened an understanding of the 
action of light on the silver salts. It is quite certain that the al- 
chemists of the sixteenth century knew of the aqueous production of 
silver chloride. 

Again we see a dormant period in the progress of the discovery of 
photography, which extends to the end of the eighteenth century. One 
of the men to whom great credit is due in this celebration, dis- 
covered again not photography but as he named it heliography. 
Joseph Nicephore Niepce (1765-1833), educated for the priesthood, 
therefore equipped with a knowledge of the humanities and a training 
in elementary science, was drawn into the vortex of the wars of the 
French Revolution. He was discharged from the army at his request, 
being debilitated by a fever which at the time raged both in the 
army and among the civilian population. 

Niepce's part in the invention of photography is best stated in his 
own words. He described his process as "automatically fixing by 
the action of light the image formed in the camera obscura and the 
reproduction by printing with the aid of known processes of engrav- 
ing." Niepce experimenting with lithography (1813-1815), then 
new in the reproductive process, attempted to obtain designs on stone 
and metal by the action of light instead of by manual drawing, and 
thus produced etched intaglio plates. He used diaphragms in his lens 
and added bellows to his camera. His first camera images were ob- 
tained in 1816, at the end of which year, being unable to fix his paper 

256 E. EPSTEAN [J. S. M. P. E. 

negatives, he abandoned the use of silver chloride and began experi- 
ments with asphaltum. While successful in the copying of engravings 
by contact, he turned back in 1826, substituting glass for metal and 
paper, to intaglio etching of images obtained in the camera. But he 
did not succeed in reproducing the middle tones, and in that year 
1826 Daguerre heard of Niepce through the Paris optician Chevalier, 
and in 1829 we find Niepce sending to Daguerre "a view from nature 
engraved on a silvered pewter plate." He met Daguerre personally 
in August, 1827, on a trip through Paris. At that time Daguerre's 
progress had resulted in nothing but fantastic experiments, without 
any significance in obtaining images by the action of light, while 
Niepce had achieved actual results before the end of 1822. Toward 
the end of 1827, while visiting his dying brother in England, Niepce 
presented to the Royal Society a short memoir entitled "Heliog- 
raphie, dessins et gravures." Since, however, he did not disclose the 
details of his manipulations the communication was returned, un- 
read, by the Society. Returning to Paris in January, 1828 he was 
urged by his friends during his stay, which was prolonged until the 
end of February, to join Daguerre in perfecting and exploiting his 
invention. It was in 1829 that Niepce first used iodine to blacken 
the silvered background of his images. In December of that year 
articles of partnership were drawn at Chalon-sur-Sa6ne between 
Niepce and Daguerre, on a visit Daguerre paid to Niepce for this 
purpose. Niepce died on July 5, 1833, in his sixty-ninth year. 

Louis Mande Daguerre (1767-1851), the other pioneer honored at 
this Centenary, had none of the culture and scientific training which 
Niepce enjoyed in his youth. He was preeminently an artist, blessed 
with imagination, seeking fame and publicity, and fortunate in having 
powerful friends. We have no record of his having had any prepara- 
tion for chemistry or optics of photography. But he showed a positive 
genius for adapting the ideas of others. His share in the invention of 
photography was not disclosed until six years after the death of his 
partner, to whom little credit was given in the publication of the da- 
guerreotype process. Having been sent to Paris in his youth to study 
art, he eventually, in collaboration with the distinguished painter, 
Bouton, created the Diorama, a marked improvement on the pano- 
rama. Incidentally, the panorama was introduced in Paris by the 
American, Robert Fulton, the inventor of the steamboat, during a 
visit from 1800-1804. Daguerre's novel lighting effects added to 
the mobility of the scene and to the attractiveness of the colors in the 


views displayed. Daguerre was made a Chevalier of the Legion of 
Honour in 1824 and it is said that the profits of the Diorama in the 
same year amounted to two hundred thousand francs. It is this 
financial success which permitted him in his leisure time to study 
and to make the experiments for finding the means of fixing the 
image obtained in the camera obscura. The Diorama burned on 
March 3, 1839, inflicting a serious financial loss on Daguerre. The 
fact is indisputable that Daguerre was the inventor of the daguerreo- 
type, and one of the inventors of photography. He must be given 
credit, as the first to recognize the light sensitivity of iodide of silver 
as well as the property of vapors of mercury to reveal the latent image. 
Whether he discovered these things by chance or whether he built 
on the pioneer knowledge of Niepce and others before him can not 
rob him of this honor.* He died on July 10, 1851, in his eighty- 
fourth year. 

The earliest information given to the public about the daguerreo- 
type was the report made by Arago to the Academy of Sciences on 
January 7, 1839, as chairman of the committee, consisting of Hum- 
boldt, Biot, and himself, appointed to visit Daguerre. His speech 
before the Chamber of Deputies on July 3, 1839, was followed 
by a similar address by Gay-Lussac in the Chamber of Peers on July 
30th, in support of the bill acquiring the purchase of the daguerreo- 
type and diorama by the French government. A few days later the 
Minister of the Interior instructed Arago to promulgate the processes 
to the world, and this Arago did in his address to the Academy of 
Sciences on August 19, 1839. This splendid gesture of the French 
government in freely giving this portentous discovery to the world 
can not be emphasized sufficiently. 

Arago's famous address to the Academy contained no technical de- 
tails. These were later printed in the official handbook of daguerreo- 
typy: Historique et Description des Precedes du Daguerreotype 
et du Diorama, written by Daguerre, which passed through several 
editions and appeared in most foreign languages before the end of 
the year. No previous discovery in history had awakened such uni- 
versal interest. 

* Briefly, the Daguerre process is as follows : A metal plate is thoroughly cleaned 
and polished and is then coated with silver, which is, in turn, highly polished. 
Metallic iodine is then sublimed on the silver coating, producing the light-sensi- 
tive silver iodide. After exposure the image is developed by fumes of mercury 
and is fixed with sodium thiosulfate, or hypo. 

258 E. EPSTEAN [J. s. M. P. E. 

Into this chorus of universal praise, however, there came a dis- 
cordant strain from England. Daguerre, in England alone, had pat- 
ented his invention. Talbot, the English scientist, claimed priority 
for the invention of his process of "photogenic drawing," which he 
communicated to the Royal Society on January 31, 1839. 

Let us look into the history of the beg nnings and development of 
photography in England. 

Thomas Wedgwood, during the years from 1792 to 1800, carried on 
experiments which he published in the Journal of the Royal Institu- 
tion, London, under the title "An Account of the Method of Copying 
Paintings upon Glass, and of Making Profiles, by the Agency of 
Light upon Nitrate of Silver, Invented by T. Wedgwood, Esq., with 
Observations by H. (Sir Humphry) Davy." Wedgwood was the first 
to conceive the idea of delineating the form of objects by the action 
of light, but he died without having found the means of fixing (mak- 
ing permanent) these photographic images. 

Sir John (John Frederick William) Herschel (1792-1871), a great 
scientist, who knew and applied the axiom that science without 
philosophy was like the body without mind, directed his researches 
to the physical laws governing chemical reactions. It is he who 
pointed out that hyposulfite of soda is the best fixing agent. 

After careful research, I do not hesitate to state that it was Sir 
John Herschel who coined the word "photography." Dr. Erich 
Stenger's claim that it was the German astronomer Madler who first 
used the term (February 25, 1839) was dispelled in my mind at the 
time of a memorable visit which I paid to Miss Hardcastle, Sir John's 
granddaughter, who resides in Observatory House at Slough, near 
London the home of Sir John. I found there considerable cor- 
respondence between the two astronomers, and I have no doubt that 
a close search would disclose the use of the word in Sir John's 
correspondence with Dr. Madler before the publication in the news- 
paper column cited by Professor Stenger. 

William Henry Fox Talbot (1800-1877), philologist and arche- 
ologist, states: "In the spring of 1834 I began to put in practice a 
method of employing . . . the property . . . possessed by nitrate of 
silver ... its discoloration when exposed to the violet rays of light." 
He published his "experiments" under the name "Photogenic Draw- 
ing" in 1839, explaining the preparation of photogenic paper, the 
washing, drying, and coating of it and his success in increasing its 
sensitivity exposure of five minutes. It was early in 1840 that the 


Calotype process (kallos meaning beautiful in Greek) reached the con- 
tinent but daguerreotypes were preferred, at least until Blanquart- 
Evrard perfected Talbot's process. The great advantage of the 
Talbotype was, of course, its ability to multiply the record obtained 
in the negative by any number of positive prints. 

We must not pass over this period without mentioning the Scot, 
Mungo Ponton, who laid the foundation for the present relief and 
other reproduction processes by announcing the light-sensitive prop- 
erty of bichromate of potash. 

During all this time improvements in the design and construction 
of cameras and lenses were introduced, new researches in photo- 
chemistry and innumerable methods of making photographic copies. 

A short American note may be given place here. In no other 
country in the world was daguerreotypy more enthusiastically re- 
ceived or so widely practiced as in America. A very complete account 
of the early American procedure in daguerreotypy, by Dr. J. W. 
Draper, of New York was published in the London and Edinburgh 
Philosophical Magazine for September, 1840. 

Daguerreotypes and Calotypes, however, were shortly to be dis- 
placed by the wet collodion process. Domont and Mnard recognized 
in 1847 the solubility of certain kinds of gun cotton in ether and al- 
cohol, giving us collodion, the name of which is derived from the 
Greek word denoting "like glue sticky." The credit for its first 
use in photography, January, 1850, is ascribed by Dr. Eder to Gustave 
le Gray in Paris. A closer study of the subject, however, confers the 
merit of introducing the first practical collodion process on the 
Englishman, Frederick Scott Archer. It displaced all previous 
methods in the decade preceding 1860, and for twenty years the wet 
collodion process occupied the first place among photographic nega- 
tive methods. In the seventies along came the bromo-silver dry 
collodion emulsion with excess of silver nitrate, followed, late in that 
decade, by gelatine bromide-silver emulsions, alkaline development 
the gelatine dry plate era. Here we meet George Eastman, introduc- 
ing the stripping film and roll holder, with later the Kodak camera 
and daylight-loading roll-film modern photography. 

Chronology now leads us to interject here brief mention of stereo- 
scopic photography. The principle of binocular vision was known 
in remote times but just a hundred years ago, the English physicist, 
Charles Wheatstone, of Gloucester, England (1802-1875), invented 
(1838) the mirror stereoscope, through which one viewed two slightly 

260 E. EPSTEAN [j. s. M. P. E. 

dissimilar images of the same object, as seen by the two eyes, and ob- 
tained a single image having the natural solidity or relief of the object. 
In Wheatstone's instrument, of course, only geometrical designs 
could be used. Figures and scenes were unattainable until pho- 
tography supplied the means by making two simultaneous exposures 
of the same subject with two lenses placed equally apart from a 
median line. 

Sir David Brewster (1781-1868) replaced Wheatstone's mirrors 
with round prisms and in 1844 produced a practical apparatus, which 
we know as the refracting or lenticular stereoscope. And it is here that 
we find the first liaison with animated photography. 

The chrysalis from which the metabulous, beautiful, brightly 
colored butterfly our cinema emerged, seems to have been the 
stroboscope strobos is derived from a Greek word meaning "a whirl- 
ing." But a thousand years before 1833, the year when, within a few 
months of each other, the Belgian Plateau and the Austrian Stampfer 
developed their inventions, a Roman poet, Lucretius Careus, wrote 
a verse practically dealing with "moving pictures." Translated from 
the Latin it is something as follows : 

"Verily, it is no miracle when images move their arms and other 
members of their bodies around, in rhythmic time. Indeed, as one 
passes another appears in different pose, the former seems to have 
changed its gestures. The change of course must take place rapidly." 

However, Lucretius expresses only the fact of the persistence of 
vision, not the mechanics or the demonstration. 

Wilfred Funk in his book "So You Think It's New," attempts to 
go still farther back and writes: "Movies? They had them in far-off 
Greece. Pictures were painted on pillars in progressive fashion, the 
idea being to ride by them on horseback and thus get the effect of 
motion. Then some smart inventor devised a better method. He 
painted a series of pictures in spiral sequence on a single revolving 
pillar. This was spun by a rope and thus the audience enjoyed the 
first cinema." 

Plateau and Stampfer painted moving figures, for instance, that of 
a dancer, on the periphery of a disk and on that of a cardboard they 
cut slits, the number of which depended on the series of subjects 
and the speed of the motion. These, turned quickly by hand, re- 
volved on their axes in front of a mirror, producing the illusion of 
movement in the figures. 


Faraday took up the subject of dividing the apparent animate 
movement of objects from the inanimate and vice versa. He read a 
paper before the Royal Society in 1831 on "A Peculiar Class of 
Optical Deceptions Showing Wheel Phenomena." 

Plateau called his apparatus phenakistiscope, phantasmascope, and 
phantascope. In Austria they were called zoetropes and other names. 
In 1833-1834 the Englishman Homer described the "marvel drum." 
The Scotch physicist Maxwell constructed such a drum with optical 
adjustment by inserting concave lenses into the viewing slits of the 
drum. The American patent of A. B. Brown, August 10, 1839, is the 
first to mention the rapidly changing exposure, interrupted with the 
aid of a rotating shutter and at the same time simultaneously inter- 
rupting the picture plate. This arrangement corresponded to the 
Maltese Cross of modern motion picture apparatus and presents in 
its essential characteristics the modern motion picture machine. 

I have no doubt you are better informed than I am on the develop- 
ment of the motion picture industry in the photographic field, its 
cameras and accessories, its reproduction of color, and its synchroni- 
zation with sound. At any rate, the technical journals specializing 
in motion picture engineering and production give a much better 
presentation of the subject than I could possible do. However, my 
cursory study of the subject and the information gained from the 
Historical Committee of your Society have given me certain informa- 
tion which I have combined in the following paragraphs. 

Edward Muybridge, born in England in 1830, emigrating to Amer- 
ica, became a professional photographer and was appointed direc- 
tor of Photographic Survey of the California Coast. In 1872 he at- 
tracted the attention of Governor Leland Stanford of California, who 
was a lover of horses and kept a racing stable. A wager on the ques- 
tion of whether a horse when running at full speed touched the ground 
with one or more feet, led Governor Stanford to the desire of register- 
ing this motion. At about the same time a Frenchman, Jules Marey, 
pursuing an investigation along the same lines, had devised a system 
for the analysis of movement, which he called Chronography. Gover- 
nor Stanford, who heard of this, had the happy idea to settle 
the wager by the aid of photography, an idea quite novel when 
we consider photographic technic at that time. Marey had never 
thought of such a possibility but Muybridge practically devoted his 
whole life to the perfecting of motion photography. In the analysis 
of movement Marey and Muybridge kept each other informed of the 

262 E. EPSTEAN [J. s. M. P. E. 

progress of their work and the experiments of these two men make 
an interesting study. 

Researches by Terry Ramsaye, reported in "A Million and One 
Nights the History of the Motion Picture," indicated that little or 
no progress was made in the solution of the problem by Muybridge 
and that Governor Stanford finally called in an engineer, John D. 
Isaacs, who worked out the fundamentals of the scheme, tried out 
the scheme successfully, and then turned it over to Muybridge. Dur- 
ing the succeeding years, Muybridge applied these ideas with con- 
siderable skill, but did not show any originality in improving upon 
them. The date when Isaacs obtained satisfactory pictures by this 
method was about 1882, although Muybridge has often been er- 
roneously credited with working out the scheme several years prior 
to that date. He died in 1904. 

Ducos du Hauron patented in 1864: "An apparatus having for its 
purpose the photographic reproduction, in any quantity, of a scene 
with all the changes to which it is subjected during a specified time." 
The apparatus was never constructed. The details of the patent 
were never published and his methods are unknown today. He 
was far ahead of his time. His arrangement of rotating lenses was 
realized thirty years later by the American Jenkins. 

C. Francis Jenkins (1867-1934) played a noteworthy role in con- 
nection with motion picture photography in America. Jenkins was 
the founder of the Society of Motion Picture Engineers. He con- 
structed in 1893 a motion picture camera called the "Phantoskop" 
which was described in the "The Photographic Times," Vol. 25, p. 2, 
July 6, 1894. A peep-hole type of viewing machine was also invented 
by Jenkins and a patent, U. S. No. 536,539 was issued to him on 
March 26, 1895. 

Research by your Historical Committee has shown that these early 
devices of Jenkins had no commercial practicability, and that it is 
Thomas Armat, rather than Jenkins, who is entitled to major credit 
for the design of the first successful motion picture projector. In 
subsequent years, Jenkins devised and developed valuable inven- 
tions related to the science of motion picture engineering, among 
which the high-speed camera was one of the most successful. 

The contributions of William Friese-Greene, an English photog- 
rapher, and those of our own Thomas Alva Edison (1847-1931) fall 
within our own times and within the much more comprehensive com- 
pass of your own experience. 


Auguste and Louis Lumire of Lyons, France, not only coined the 
word "cine'matographe" and gave their first exhibition at Paris 
in 1895, but were also the first to place on the market remarkably 
simple and efficient apparatus for taking and projecting serial pic- 
tures in which the perforated film strip was for the first time held 
and moved by a gripper. It is, of course, well known that this firm 
had been making dry plates for years. The history of the Brothers 
Lumiere and their accomplishments deserve a special biography, 
for their services to photography in all its branches are extremely im- 

In conclusion, I can but ask you to compare your present palatial 
and itinerant motion picture camera on automobile trucks with the 
apparatus with which the early American photographers had to con- 
tend. Professor Robert Taft, in his splendid book on Photography and 
the American Scene recently published by Macmillan, speaks of "in- 
dependent photographers who were gradually pushing west (or east 
from the west coast) as the line of the frontier gradually changed." 
He speaks of C. E. Watkins of San Francisco, who was born in 
New York and went to California as a young man around the 
1850's. In 1861 ''Watkins made his first trip into the Yosemite 
Valley, which was disinguished by the fact that he took with him a 
camera constructed by himself, capable of taking a plate 18 X 22 
inches in size. The use of these large plates by a wet plate photog- 
rapher, working under the most favorable circumstances, was at- 
tended with considerable difficulty. It was a feat of no mean skill 
to flow the collodion on these plates, obtain a uniform film, and then 
sensitize, expose, and develop them when they were still moist. . . A 
twelve-mule train was necessary to transport Watkins and his sup- 
plies to the valley, and five of these mules carried his equipment as 
he made his photographic tour of the region. As each photograph 
was made the darkroom tent had to be unpacked and set up, the 
plates prepared in the small tent, and developed immediately after ex- 
posure. The equipment was then repacked and the mule train moved 
on to obtain the next view." 

The daguerreotype of 1839, the Centenary of which we are com- 
memorating this year, has developed into the ubiquitous photography 
of today, invading every field of art, science, and industry, of which 
the motion picture is such a brilliant example it has been a long road 
to Hollywood! 

R. R. McMATH** 

Summary. Taking motion pictures of celestial phenomena that show change 
is not as simple as it would first appear. Work on spectroheliokinematography was 
started in 1928, and in 1931 the instrumentation was donated to the University 
of Michigan by the founders of the McMath-Hulbert Observatory. 

The combined tower telescope and spectroheliokinemato graph of this observatory, 
now one of the most powerful pieces of solar apparatus in the world, is described and 
some of the solar data obtained with it are discussed. 

The atoms in the surfaces of all the billions of stars accessible with 
our telescopes may fittingly be compared to minute sending stations, 
broadcasting each on its appointed multitude of narrow wave-length 
bands, preserving their allotted "channels" with almost infinite ex- 
actitude and endeavoring thus to send us certain important mes- 
sages relating to the temperature and the constitution of the 
stars in which they are located. With out telescopes, and to a far 
greater extent with those optical receiving stations we call spectro- 
graphs, we are today reading a few of the messages these distant stars 
are endeavoring to broadcast to us. 

Certain equally important messages relating to the actual spatial 
behavior and physical movements in stellar surfaces seem, however, 
permanently beyond our reach. For no telescope, existing, projected, 
or imaginable, can show a star to us as anything but a diskless point 
of light; an actual stellar diameter of a million miles or more will 
vanish almost into a mathematical point at stellar distances of tril- 
lions or quadrillions of miles. 

Thus it becomes very fortunate for our knowledge of the distant 
stars that we have a star so close at hand that we can see its disk 
and study the actual motions on its surface. The star referred to is, 
of course, our own sun, a mere bagatelle of ninety-three millions of 
miles distant, and, fortunately for the truth of the deductions we may 
make from it as to the surface behavior of stars in general, a respect- 

* Presented at the 1938 Fall Meeting of Detroit, Mich. ; reprinted from 
Scientific Monthly (Nov., 1938) p. 411. 

** The McMath-Hulbert Observatory, University of Michigan. 


able, run-of-the-mill, middle-aged star, neither very hot nor very cool 
as stars go, and neither a giant nor quite a dwarf among its millions 
of brother suns. The entirely average position of our sun as to size, 
luminosity, mass, and other characteristics thus facilitates and makes 
more probable any deductions we may wish to draw from it in ap- 
plication to more distant suns. To repeat, any study of the stars of 
our universe must start with and be based upon a study of our nearest 
star the sun. 

About twelve years ago the writer, with two most helpful col- 
leagues Judge Henry S. Hulbert and the late Francis C. McMath, 
my father decided that a fallow and hitherto neglected field lay 
invitingly open for research through the application of the motion 
picture to such astronomical phenomena as exhibit rapid motion or 
change. A small, but most completely equipped telescope was de- 
signed and built for the highly exacting technic of the motion picture 
as applied to astronomical photography, and this installation was 
located at Lake Angelus, about five miles to the north of Pontiac, 
Mich. The instrumental equipment was gradually augmented and 
improved through several years of gradual evolution and develop- 
ment, too long and too technical to detail here, and in 1931 the plant, 
under the name of the McMath-Hulbert Observatory, was deeded 
by its founders to the University of Michigan. 

Our initial aims were frankly educational. We envisaged the mani- 
fold assistance that carefully planned astronomical films would give 
to the work of astronomical instruction in schools and colleges. How 
much more effective it would be, we reasoned, to project for a class a 
three-minute film, showing, for example, the rotation of the planet 
Jupiter on its axis and the revolutions of its moons about the planet, 
than merely to lecture to a class that such things were happening. 
Many thousand feet of such educational films were taken by the Mc- 
Math-Hulbert Observatory of planets and their satellites, the phe- 
nomena of sunrise and sunset on the slowly rotating moon, and simi- 
lar subjects, and a considerable number of educational reels of such 
types have been shown to scientific societies and distributed to schools 
and colleges. 

It is with a feeling of some regret that we have had to drop most 
of our efforts to provide purely instructional adjuvants for astronomi- 
cal teaching we hope only temporarily for we are still firmly con- 
vinced as to the great value of such astronomical films for the in- 
structor as well as for the student. 



[J. S. M. P. E. 

The reason for this temporary abandonment is comparatively 
simple; it has come about merely because a further extension of this 
motion picture technic to that nearest star we call the sun has opened 
up such new and astonishingly inviting fields of scientific research 
that we have been compelled, willy-nilly, to devote every waking 
moment to a new and fascinating field of most useful scientific 
work on the sun the actual depiction of the storms around sun-spots, 
and the intricacy of the motions of the mighty gaseous prominences 

FIG. 1. 

The McMath-Hulbert Observatory of The University of Michigan, 
from a photograph by Sidney D. Waldon. 

that rise for many thousands of miles above the solar surface, and 
move and change and disintegrate with speeds that range from a few 
miles per second up to explosive velocities of several hundred miles 
per second. The many puzzles which are exhibited by these new 
pictures, some of which remain as yet unsolved, force us to the conclu- 
sion that our initial purely educational aim must give ground for 
the present to a program of pure scientific research. 

There are several respects in which the new motion pictures of 
solar phenomena are unique, and we may be pardoned for assembling 
certain of their outstanding characteristics at this point. 


(1) These pictures are in a very real sense "modern," inasmuch as 
the first solar films taken with the new McMath-Hulbert tower tele- 
scope were made on July 2, 1936, one day after the completion of the 

(2) They are definitely unique, because no other installation at 
present exists which has the instrumentation for similar motion pic- 
ture records of solar phenomena. 

(3) They were the most nearly continuous records of solar phe- 
nomena ever made, and in this factor, as will be noted below, lies 
perhaps the largest portion of their value as scientific documents for 
research purposes. Photographs of the solar surface in white light, 
and spectroheliograms of solar prominences in the light of calcium 
or hydrogen have been taken for several decades, but most of these 
were effectively "stills," to use the terminology of the motion picture 
studio. Such stills, taken at time-intervals of an hour or less, have 
given valuable data as to the changes occurring in solar features; 
the continuous character of these new records shows, however, the 
changes as they are taking place, and not only make possible a more 
detailed study of the mechanisms underlying the phenomena, but 
also have brought to light a mass of new details, hitherto unsuspected, 
and unrecorded in the still pictures of the past. 

There are in the world to-day seven tower telescopes for studies 
of the sun; that at Lake Angelus is not only the most recent, but 
embodies many refinements of design. This instrument may be suc- 
cinctly described as a telescope which remains fixed in a vertical 
position, with an arrangement of motor-driven mirrors at the top of 
the tower, termed a coelostat, to follow the sun as it moves across the 
sky and to throw its image vertically downward; the Lake Angelus 
instrument is approximately fifty feet in height. The various mirrors 
in this optical train are of pyrex, which is peculiarly fitted for solar 
instruments because of its very low coefficient of thermal expansion. 
These mirrors are covered with a thin coating of aluminum, deposited 
by evaporation in a vacuum; due to this use of mirrors rather than 
lenses, we have an achromatic telescope that is exceedingly rapid 
photographically. For this reason, the exposures with the Lake 
Angelus apparatus may be made very short; exposures on solar 
prominences in current work range from ten to thirty seconds, where 
most other installations must count their exposure times in minutes 
rather in seconds ; such short exposures make for a record that is prac- 
tically continuous. 

268 R. R. MCMATH [j. S. M. P. E. 

At the bottom of the tower the solar image formed by the mirror 
train falls upon the slit of a spectroheliograph. This rather technical 
instrument may be briefly described for the layman as a spectrograph 
which passes the light from the solar image through a narrow slit and 
then through a lens to a grating or prism which is located in a heavy 
rotatable steel cage in a well thirty-five feet deep beneath the tower. 
The grating disperses and spreads out the light in the form of a spec- 
trum and reflects this spectrum through the same lens back to the 
upper end. Here a second slit is installed that is the "heart" of 
the apparatus. With this second slit we pick out some one particular 
wavelength of some element in the solar spectrum and throw all the 
rest of the solar light away. Solar prominences, for example, are par- 
ticularly rich in the elements calcium and hydrogen. Thus we may 
pick out one definite wavelength of calcium and secure a photograph 
of a narrow strip of the sun where the solar image falls upon the narrow 
slit, in calcium light only, where an ordinary photograph in "white" 
light would show nothing, because of the overpowering brilliance of the 
light coming from other chemical elements in the sun. But a photo- 
graph of a narrow strip of the sun in calcium light would be useless 
and almost meaningless; what we need is a calcium or a hydrogen 
light picture of a considerable area, either of the solar disk itself or 
of an area of the solar limb where some large prominence is seen in 
profile. To secure such a picture of an area, the first slit is moved 
back and forth over the chosen area of the solar image and the second, 
or "picking-out" slit is given a precisely equal but exactly opposite 
motion so as always to receive the calcium wavelength of the spec- 
trum reflected from the grating, and that wavelength only. 

The result of this scanning process, performed twice a second, is a 
calcium or a hydrogen picture of an area. Some other elements may 
be selected as well, in case we wish to secure an iron picture or a 
helium picture, and all these pictures in the light of some chosen ele- 
ment would ordinarily be entirely invisible, but are made possible 
only by this process of sorting out a definite wavelength and discard- 
ing all the rest of the light from the sun. 

The above brief and schematic description, manifestly, can give 
but a slight idea of the actual complexity of the apparatus, some con- 
ception of which may be derived from the fact that there are about 
forty small electric motors scattered over the tower mechanisms from 
the coelostat at the top to the grating cage down in the well, and each 
of these is controlled by its individual push-button. In these re- 


spects the present installation is doubtless the most convenient in ex- 
istence, as the observer at the spectroheliograph head can perform any 
adjustment or manipulation without leaving his station, merely by 
pressing an electric push-button. 

The apparent complexity of certain features of the mechanism of 
this tower telescope is, in some senses, merely a necessary consequence 
of the exacting technic that has been found indispensable for the tak- 
ing of satisfactory motion pictures of this and other celestial phe- 
nomena. A "run" or "scene" may comprise anything from a few 
hundred to over a thousand separate pictures on the film; the word 
"frame" is customarily used for these individual pictures; six or eight 
hours of continuous work will ordinarily go into a run comprising a 
thousand separate frames. 

Manifestly, all the frames of a scene must be as perfectly registered 
as possible, to avoid flickering and unsteadiness on the screen. Early 
in the work on the moon and planets that preceded this solar work, it 
was found that no existing form of telescope drive gave sufficient 
accuracy. Accordingly, merely as a by-product of the larger pro- 
gram, and after four other methods had been tried and found want- 
ing, a new and improved form of telescope drive was devised, based 
upon an infinitely flexible and instantly variable control of the input 
electrical frequency to the telescope drive motor, secured through 
resistance-ballasted thermionic tubes. This form of telescope drive 
is known as the McMath-Hulbert electric drive ; it brings it to pass 
that the telescope becomes an automatically following instead of a 
manually guided apparatus; it has since been adopted for the drive 
of the McDonald reflector in Texas, for three telescopes at Lick Ob- 
servatory, and is under consideration for other projected large telescope 
mountings. The instruments at Lake Angelus were also the first to 
employ a similar accurately controlled drive in the declination com- 
ponent, in addition to the ordinary motion given in the right ascension 

In the astronomical motion picture technic, it must also be possible 
to arrange for any probable desired duration of the actual exposure, 
as well as for the duration of the "dark time" between exposures. A 
gearing train in an underground control room adjacent to the tower 
makes possible the selection of these times and controls the shutter 
of the special motion picture camera. A description, or even a bare 
tabulation, of all the necessary mechanical details is, however, mani- 
festly impossible in a general article. Only one additional desidera- 

270 R. R. McMATH [J. S. M. P. E. 

turn may be noted. The hundreds of separate frames in a scene 
would have scant scientific value as records of motion and change if 
accurate timing arrangements were not provided. Accordingly each 
individual frame automatically makes a record of its time electrically 
on a continuously running chronograph in the underground control 

With an exposure of twenty-seven seconds on a solar prominence 
and a dark time of three seconds, two frames will be taken per minute ; 
they will be projected on the screen at the customary rate of sixteen 
per second, or 960 frames per minute. Thus it will be evident that the 
projected picture will have a "compression factor" of 1 :480. Such a 
compression of the record is not only inevitable, but a very distinct 
advantage, rather than a detriment. 

Suppose, as is not at all unusual, that a bright knot is seen to form 
100,000 miles above the solar surface and then to descend at the 
rate of 40 miles per second, about average as solar prominence ve- 
locities run, but still 80 times the speed of a high-power rifle bullet. 
Its total time of descent to the sun will be forty-two minutes. In- 
stead of having to wait that long in our seats to see the history of this 
descending knot, the above compression factor of 1 : 480 reduces it to 
about 5 seconds, and a scene which is made up of several such knots 
in motion will occupy the very convenient interval of 20 or 25 
seconds and appears practically continuous in its record of motions 
and changes. 

By design, considerable space has here been given to an outline of 
the technic of the motion picture as adapted to an astronomical end, 
and the apparatus necessary for the purpose, in order to emphasize, 
not only the more difficult features of the research on its mechanical 
side but also the unique character of the resulting record. 

During the seasons of 1936 and 1937 over ten thousand feet of 
standard 35-mm. film were exposed in the new tower telescope on 
the solar prominences or on features of the solar disk itself. Even 
though every possible mechanical convenience or electrical adjust- 
ment has been provided, and even though this tower telescope has 
been pronounced to be the most rapid, flexible, and convenient in 
existence, the total amount of labor and attention involved in taking 
over one thousand separate photographs in the run on a clear day 
which may extend from 8 A.M. or earlier till 6 P.M. is very considerable. 
It is a pleasure to make acknowledgment at this point to my two col- 
leagues and to those who have assisted in the somewhat complicated 

Mar., 1939] 



FIG. 2. The 50' tower telescope of the McMath-Hulbert Observatory from 
a drawing by Russell W. Porter. 

technic of solar prominence photography and measurement to our 
research associate, Dr. Edison Pettit, of the Mount Wilson Observa- 
tory, and to Harold E. Sawyer, assistant astronomer, and John 
Brodie, assistant, in the McMath-Hulbert Observatory; others have 
given assistance for shorter periods. We owe also a special debt of 

272 R. R. McMATH [J. S. M. P. E. 

thanks to Dr. Heber D. Curtis, director of the observatories of the 
University of Michigan, who has, from its very inceptance, given 
every encouragement to this program of solar research and every 
assistance within his power. 

These films, when projected under proper conditions, show scenes 
of unexampled grandeur, and radically change our preconceived no- 
tions of the surface of a star. Though we knew from the "still" 
photographs of the past that the sun's surface was marked by con- 
stant activity as manifested by those solar storms called sun-spots, by 
the flocculi and by the prominences, these films for the first time 
bring to us the actual motions in a continuous record, which we may 
repeat as often as we need for our scientific studies. These motion 
pictures very effectively change our conception of a star's surface 
from something at least relatively static to a picture that is intensely 
kinetic; we begin to realize that the surface of a star is an unending 
maelstrom of motions due to titanic forces whose precise nature can 
not as yet be regarded as completely explained. 

Even though we are astronomers, we are very human, and we too 
derive much the same pleasure as does the layman who sees these 
films and is enthusiastic in his praise of them, viewed merely as in- 
spiring spectacles. And yet, strange as it may seem, we who are tak- 
ing and studying these new records of solar activity take rather amiss 
the enthusiastic praises we hear from laymen or from scientists in 
other fields who apparently regard them as merely interesting 
"movies." We feel quite strongly that the magnificence of these 
displays is, in many respects, only a very secondary consideration in 
our evaluation of these pictures as scientific records, from which facts 
of very definite value are being derived as to the actual nature of 
the surface of a star. 

"Conflagrations," explosions, skyrocket sheaves of light like the 
grand finale of the 4th of July celebrations of our boyhood, are all 
admittedly inspiring when we realize the tremendous speeds that are 
actually involved, the temperature of more than 10,000F, that our 
pictures embraces an area 150,000 miles high and 200,000 miles wide, 
and that our earth would be but a small disk on the same scale and 
quite unimportant in comparison to the mighty flames and streamers 
of incadescent gas that form these solar storms. Yet to us the mo- 
tions and laws of motion that we are deriving and the nature of the 
mysterious forces that seem eternally operative on the surface of a 


star are much the more important considerations as we view these new 

This new method of attack on the problems exhibited by the surface 
of a star is still too youthful to admit of explanations of each and 
every phenomenon observed. Fresh puzzles too frequently show 
themselves in each run on a new and active prominence, and if the 
history of our past work is any criterion, the coming season of 1938 
will bring to light as many new features as have those of the two 
preceding years. The complexity of some of the more active promi- 
nence displays frequently baffles description, and we often find that 
the only way to be sure of all that is taking place is a repeated showing 
of the film ; frequently we will notice some minor peculiarity or puzzle 
in the tenth or twelfth showing that had previously escaped us and 
had, of course, never been suspected in the still pictures of the past. 

While, as already noted, we are still working on many of the puzzles 
presented, and are withholding a more precise formation of hypotheses 
till more data have been collected, some of the results of the work on 
the sun with the new tower telescope and our improved motion pic- 
ture technic may be assembled as follows, either in more general 
statements or in descriptions of isolated phenomena. 

(1) It has become necessary to add three subdivisions to Dr. 
Pettit's accepted classification scheme for solar prominences, to 
include three new types of prominence whose existence was not hither- 
to suspected. These are: 

(a) Surges. These are very short-lived prominences like spear- 
heads of flame, that stab upward 1000 to 10,000 miles or so from the 
solar chromosphere and as rapidly subside again, with a total life 
period of only a few minutes. As seen in profile in runs on promi- 
nences, the limb of the sun will occasionally exhibit an almost con- 
tinuous activity of this type. In pictures of the solar disk proper, 
the sudden short-lived splotches of brilliant light that appear and dis- 
appear in areas about sun-spots are believed to be these same surges, 
seen from above. 

(b) Ejections. This name has been given to the balls of luminous 
chromospheric matter thrown out of sun-spot areas like Roman- 
candle displays. They are relatively faint and seem to leave the 
sun without returning. In one or two cases these balls seem rather 
more like hollow spheres or perhaps in the form of smoke rings; it is 
difficult to decide with the material now available. 

(c) Coronal Type Streamers. These are very puzzling. In such 



LT. S. M. P. E. 

FIG. 3. Great eruptive prominence of September 17, 1937, photo- 
graphed at The McMath-Hulbert Observatory. 

A. 14 h 50. m 69 B. 14 h 55. m 84 C. 15 h 06. m 13 GCT 

D. 15 h 09. m ll E. 15 h 14. m 31 F. 16 h 06. m 7 GCT 

Exposures A to E with 20-ft. focus mirror, F with lens of 74 inches focal 
length. In "F" the prominence goes out of the picture 1,000,000 km. 
above the sun. 

streamers matter appears to form, or more properly to become lumi- 
nous, at an altitude of 120,000 miles or more above the surface of the 
sun and then to descend in successive streamers to the solar surface. 
These coronal streamers are generally rather faint and have never 
been detected before. 


(2) Several very interesting examples of violently eruptive promi- 
nences have been recorded. For one of these, taken in September, 
1937, though the entire period covered by the scene was only 80 
minutes, the upper portions could not be kept within the motion 
picture frame in spite of three successive changes to shorter focal 
lengths; the total height was about 620,000 miles, which held the 
world's record until the recent record of 900,000 miles for a promi- 
nence photographed at Mount Wilson. The velocity of this Lake 
Angelus prominence reached 432 miles per second ; as this is consider- 
ably greater than the "velocity of escape" under gravitational attrac- 
tion at this distance from the sun, this is believed to be the first 
recorded instance where we have observed matter shot out into space 
beyond the sun's attraction, though such possibilities have long been 
recognized in theory. 

(3) Arch Types. Several great arches of unusual interest have been 
recorded. In one of these it was nearly 100,000 miles between the 
"feet of the rainbow." Though there was no noticeable accretion of 
material at the top of this arch, luminous knots of gas are observed 
continuously descending to the sun in both directions from the summit 
on the arch. Why? 

(4) Predominance of Matter in Descent. Even if we include the 
prominences of eruptive type mentioned under 2 above, perhaps 90 
per cent of our prominence scenes record matter in descent only. On 
a number of great "banyan-tree" prominences, with multiple stalks or 
trunks connecting the enlarged upper portions to the chromosphere, 
bright nodules of matter will be observed spiralling downward along 
the "trunks." We have mentioned above under Ic the growth lumi- 
nescence in, or actual formation of faint clouds high above the sun, 
from which the coronal type streamers descend, phenomena which 
seem to necessitate the postulation of some form of solar chromo- 
spheric atmosphere intermixed with the corona. 

Much the same class of phenomena are exhibited in lower bright 
streamers of the beautiful "set-pieces" of a fountain type; the mo- 
tion of descent is here often clear and rapid ; any corresponding as- 
cent of matter on a possible rising arm of the complete trajectory is 
either very much fainter or entirely absent. Astronomers who see 
these films for the first time frequently attempt to explain this curious 
phenomenon by ascribing the invisibility of the ascending side of the 
streamer to the Doppler effect, arguing that some velocity in the line 
of sight moves the wavelength under observation "off the slit" for the 

276 R. R. McMATH [J. S. M. P. E. 

ascending branch and implying that these films give a partial rather 
than a true picture of these motions. We are utterly unable to accept 
this explanation in the vast majority of cases, for we have noted only 
two cases of sudden brightening of small patches near the chromo- 
sphere that may possibly be due to the Doppler effect, that is, to a 
velocity in the line of sight sufficient to bring a different wavelength 
and hence a previously unobserved detail into the slit of the instru- 
ment. But an elementary consideration of the geometry of these 
prominence arches would predicate roughly equal velocities in the 
line of sight for matter at corresponding portions of the hypothetical 
ascending or the descending branches of the arch. Moreover, al- 
though workers in the past have maintained that narrow slits are 
an inescapable necessity in spectroheliographic work, we have, as a 
result of numerous experiments with wider slits, taken beautifully 
clear and sharp spectroheliograms in the H alpha line of hydrogen with 
both slits 0.5 mm. (about one fiftieth of an inch) in width. This width 
would necessitate a difference in radial velocity of about 110 km. per 
second (68 miles per second) to move a portion of our picture off the 
slit and thus render some parts invisible. While higher velocities are 
occasionally observed in eruptive prominences, such velocities have 
only rarely been found in these arch trajectories. 

The phenomenon remains a puzzle. It is apparent that what goes 
down very probably came up, but why should the upward journey be 
predominantly invisible? Is it that the gases on their upward path 
are in some different temperature or ionization state, changing back 
to another and photographically recordable state soon after passing 
the crest of their trajectory? Data are being collected that may even- 
tually give an answer to this pressing and difficult question. 

(5) Previous work had detected no motions within the dark hy- 
drogen flocculi. We have been fortunate enough to "catch" and to 
photograph for a total elapsed time of 5 x /2 days an enormous hydrogen 
flocculus whose total length must have been of the order of 700,000 
miles, extending over a considerable portion of the solar disk. Its 
internal motions and its final disintegration were clearly recorded. 
So far as is known, this is the first case where the life-history of one 
of these dark hydrogen flocculi has been followed from its first appear- 
ance to the end. 

(6) Abundant confirmation has been secured in the study of mo- 
tions in prominence streamers in support of the curious laws of 
prominence motion discovered earlier by Dr. Pettit. The velocity of a 


prominence or prominence formation is uniform, increasing suddenly 
at intervals. When there is a change in velocity the new velocity is 
generally a simple multiple of the previous velocity. That is, a knot 
that has been moving along a streamer, at a uniform speed of, say, 21 
miles per second will suddenly (sometimes in less than a minute) be 
accelerated to a uniform speed of 42 miles per second, without any 
apparent transition through intermediate velocities. This puzzling 
phenomenon has been studied and extended to include nearly all 
prominence types at Lake Angelus. Like some others found in the 
Lake Angelus work mentioned above, it shows that we have many 
still unknown factors with which to deal before we can secure an ex- 
planation of all the laws that govern the motion of gaseous matter 
near the surface of a star. 

Such, then, are some of the results, as well as some of the problems, 
that are growing out of the application of this new technic to the 
study of a star's surface behavior; the work is being continued as 
fast as time and money will permit. The very richness of the material 
being secured has its embarrasing features; it will easily be seen that 
the detailed measurement of the motions even in one tenth of the 
frames of a prominence picture that includes over a thousand separate 
pictures involves a great deal of time and not a little calculation. The 
number of the prominences, as well as the number and the activity 
of the flocculi and other disk features, shows an intimate connection 
with the curve of the number of sun-spots that reaches a maximum 
roughly every eleven and a third years. We have recently been 
passing through a period of maximum sun-spot activity, but we do 
not yet know what detail changes in prominence activity will be ob- 
served on our films at a sun-spot minimum. We are inclined to pre- 
dict that while we shall then have fewer prominences on which to 
work, they still will be of equal value in formulating theories of the 
surface layers of a star. Certainly only a beginning of our program of 
research will have been made until we have worked completely 
through at least one sun-spot cycle. 

At the close of his presentation, Mr. Me Math showed motion pictures of the sun 
taken with the spectroheliokinematograph described in the paper. The motion 
pictures showed the prominences and other phenomena of the sun taken under hy- 
drogen and calcium light. The types of prominences and streamers are described 
in the paper. Sun spots and other eruptions and ejections were shown. 


MR. McMATH: Please bear in mind that you were looking at atoms, and 
do not try to interpret what you have seen in terms of molecular physics. The 

278 R. R. McMATH [J. S. M. P. E. 

temperatures are at least 10,000 F, and as far as we know there are few mole- 
cules or atoms in association at that temperature. Of course, we are photo- 
graphing a very simple atom. 

MR. CRABTREE: How long do the eruptions last? 

MR. McMATH: The duration is measured in either days or minutes, the 
shortest being about 20 minutes. 

MR. KELLOGG: Mr. McMath has given us a real thrill. How nearly the 
same would the picture be if it were taken with hydrogen instead of calcium? 
Are the gases localized? Is what we saw a phenomenon in hydrogen gas alone, 
or calcium alone? 

MR. McMATH : No, it appears that the prominence is a homogeneous mixture 
of gases. They actually are about 98 per cent hydrogen gas, and the rest is 
principally calcium and helium. As we approach the chromosphere we commence 
to get traces of heavier elements, for instance, sodium. We have simultaneous 
pictures, many thousands of feet of them, taken in calcium and hydrogen, at 
precisely the same time, and the two pictures look practically alike, and the two 
gases behave alike and measure alike. 

MR. KELLOGG: Is what appears to be motion really regions of intense pro- 
gressive ionization of gas by free traveling electrons or by electromagnetic waves, 
rather than the motion of the material itself? 

MR. McMATH: It is a very long story. These prominences are seen at 
eclipses, and we have some eclipse photography under the whole integrated light 
which would eliminate some spectroscopic implications. Since we have done 
this work in neutral hydrogen atoms, as well as the ionized calcium, we believe 
that we are looking at the streaming of individual atoms. 

MR. MATTHEWS: How thick is the chromosphere? Does it vary in thickness 
from time to time? 

MR. MCMATH: It will average from between 5000 and 6000 kilometers at 
eclipses. When a picture is taken with white light with an ordinary camera, 
we get a picture of the photosphere. That is where the spots show up black. 
Just above the photosphere is a layer of gases, the chromosphere. This is the 
reversing area, from which we get the dark hydrogen line of the solar spectrum, 
known as an absorption line. In the prominences, of course, we take the picture 
in the emission line of the hydrogen. 

MR. WOLF: What do you anticipate can be done with the new 200-inch tele- 

MR. McMATH: It will probably never be used on the sun. I am on the 
Advisory Committee for the 200-inch telescope, and I wish it would be used for 
the sun, but it will not be. There are some objections to solar work with an 
equatorial telescope, not easily explained in a few minutes. 

MR. JOHNSON: In the course of the day is there a sensible change in the 
apparent motion of the sun? 

MR. MCMATH: That is due to refraction. At sunrise and sunset we get 
maximum refraction. At sunrise the sun appears in the telescope to travel 
more slowly than it does when on the meridian at noon. 

MR. MATTHEWS: Have you any explanation of why the prominences are 
drawn back in? 

MR. MCMATH: No. All the earlier work was based on material rising from 


the sun. An English group tried to explain the prominences by radiation pres- 
sure. Now we find, in, say, one hundred hours of photography, about 90 per cent 
of the pictures show material going down into the sun. All evidence obtained 
at eclipses denies specifically the existence of chromospheric material in the 
corona or in the solar atmosphere, we will say. However, we are forced into the 
postulation of some kind of solar atmosphere. The material is certainly there. 
It would not appear out of nothing. 

MR. STROCK: Are these prominences the disturbances that are correlated 
with radio fading? 

MR. McMATH: Not always. That problem is being investigated by J. H. 
Bellinger of the Radio Division of the National Bureau of Standards, and others. 
There have been certain chromospheric eruptions that have been coincident with 
general short-wave radio fadeouts on the sunlit hemisphere. We do not know 
precisely what type of activity is associated with these fadeouts. Sometimes 
very intense activity has no noticeable effect upon radio reception. The enor- 
mous eruption of September 17, 1939, had no effect upon radio reception at all, 
and yet it was very intense. 

MR. STROCK: Do we know whether these prominences are tied in with the 
so-called eleven-year sun-spot cycle? 

MR. McMATH: They occur with solar activity. The more sun spots, the 
more solar activity; and the more solar activity, the more prominences. 



Summary. Music is a study that is primarily an art; its scientific aspects have 
been recognized since ancient days. An outline is given of the physical basis of 
harmony upon which in turn are based the musical scales. A short outline of the 
historical development of the modern scale is included, the discords produced in the 
tempered scale due to natural harmonics and summation and difference tones being 
noted. In the electronic instruments the musical tones can be generated as such in the 
first instance, or may be produced as a synthesis of pure tones; instruments embody- 
ing these principles are described briefly. A method of the synthesis of musical 
qualities is described, and at the presentation of the paper, such tones were demon- 
strated using the Hammond (electric) organ, the wave-forms being shown on an 

In conclusion it is suggested that the possibility of removing the limitations of the 
traditional keyboard instruments gives an opportunity of abandoning the tempered 
scale in favor of the just scale. 

This paper deals with a topic that lies partly in the realm of art 
and partly in the realm of science; it is not clear where one ends and 
the other begins. If the question is debated as to wherein lies the 
superiority of Beethoven over Puccini, science can take no part. The 
problem is either too vague or too complicated to be dealt with on a 
precise basis. Physics can not tell us why we find Beethoven par- 
ticularly pleasing but it can explain why an error made in trans- 
posing his music from one key to another would make it disagreeable. 

Let us first look at the elementary facts of the physical basis of 
music. Music is an art; our response to it is psychological and emo- 
tional. Nevertheless if, as engineers, we set out to produce, to trans- 
mit, and to reproduce music, we are forced to translate the intangible 
into terms of the tangible. Just as a knowledge of anatomy is basic 
in the training of a sculptor or painter, so in music it is necessary to 
understand the arithmetic that forms the groundwork of the art. 

*Received December 1, 1938; presented before the Montreal Sections of the 
Engineering Institute of Canada and the Institute of Radio Engineers, Oct. 12, 
1938, and the Toronto Sections of the Institute of Radio Engineers and the Ameri- 
can Institute of Electrical Engineers, Oct. 17, 1938. 
**Northern Electric Co., Ltd., Montreal, Canada. 



There are three attributes that we recognize as essential in music : 
rhythm, melody, harmony. Rhythm, the maintenance and accenting 
of the time intervals at which sounds are produced, is the simplest 
and most obvious part of music, and is the chief characteristic of 
primitive music. Melody is the linking together of notes of different 
pitches and durations in a sequence that is pleasing, harmonious, 
and readily capable of being memorized. It is the attribute of music 
next in complexity to rhythm, and many modern types of music, 
e. g. y the Persian, consist only of single notes played in sequence and 
in rhythm the kind of music a man whistling and tapping his foot 
produces. The third attribute, harmony, is inextricably bound up 
with melody in a very complicated fashion, and is the art and science 
of sounding two or more notes simultaneously so that a pleasing 
effect is obtained, of greater richness, variety, and interest than a 
single note can produce. 

It is plain that music requires a fixed series of notes whose pitches, 
*. e., frequencies, are such that they give pleasing effects when sounded 
in various sequences, and that can be grouped in a number of ways and 
sounded simultaneously without offending the ear. What then are 
the physical realities back of such terms as "pleasing," "offending"? 
A melody sounds well when its component notes are those that sound 
well in harmony. This leads to the simple rule that has been uni- 
versally recognized for at least 30 centuries as the fundamental basis 
of music: Two notes sounded simultaneously are harmonious if the 
ratio of their frequencies can be expressed as the ratio of small integral 

From this rule, we should expect that notes with the following 
frequency ratios would be harmonious, the degree of concord 
lessening as we go down the list : 

12345 3455 
---- - etc.,-* - - -' etc. 
11111 2334 

The reason why the combination of two tones is harmonious when 
the tone frequencies have a simple numerical ratio has been the sub- 
ject for conjecture since Pythagoras, who flourished about 700 B.C. 
Pythagoras considered such harmony inherent in nature and theology; 
Confucius also solved the problem by a relapse to metaphysics. In 
the 18th century the mathematician Euler brought psychology to 
bear, and attributed the concord to our delight in method and order- 
liness, and proposed an elaborate system long since discarded for 

282 S. T. FISHER tf. S. M. P. E. 

rating the concord or discord of various combinations. Rameau 
and D'Alembert about the same time decided that since an octave 
and a 12th (octave plus fifth) were produced in nature as the 2nd 
and 3rd harmonics of a tone, it was in the nature of things that these 
should be concordant intervals. In 1862 Helmholtz proposed the 
theory that, with modifications, is generally held today. It really 
explains, not why concords are pleasant, but why discords are un- 
pleasant. The situation appears to be this : The normal human being 
gets pleasure from doing difficult things. The crossword puzzle addict 
cares nothing for simple puzzles ; the more baffling they are the more 
pleasing it is to find a solution. The sportsman who could shoot his 
partridges on the ground or his ducks in the water deliberately per- 
forms the much more difficult feat of shooting them flying. 

It appears that listening to single-note melodies is too simple, and 
so we prefer to listen to complicated tone groups rather than single 
tones. At the same time if a number of notes are sounded simul- 
taneously to form a single chord, there must be no frequencies intro- 
duced that are objectionable. If two notes do not have a simple 
numerical ratio between their frequencies, then either the funda- 
mentals or some harmonics of these will beat together to form harsh 
low-frequency beat notes, and the only notes between which tolerable 
concord exists are those combinations that do not produce such beat 

The simplest harmony exists between octaves, that is, between two 
tones where one is 2, 4, 8, etc., times the other in frequency. This 
was the only harmony used by the Greeks. It is readily obtained in 
singing, since men's and boys' voices are about one octave apart; 
in instrumental music the Greeks obtained it by inserting a bridge 
in their lyres one-third the distance along the strings. To us this 
kind of harmony sounds childish, flat, uninteresting. Later, music 
in Europe, in the first or second century B.C., used the interval of the 
5th, which is CG on our keyboard, a frequency ratio of 3:2. The 5th 
is the most important interval in modern music, and stringed instru- 
ments and pipes as far back as the 5th century B.C. were tuned to 
the intervals C, F, G, C 1 . Early in the Christian era, a 5-note scale 
became very common, both in Europe and Asia, and modern Scotch 
and Chinese music is frequently found in this scale, the notes on 
our keyboard being C, D, F, G, A. It will be found that many 
traditional melodies are played using only these notes, and that any 
tune restricted to these notes has a characteristic quality that we or- 



dinarily associate with Scotch music. This scale appears to be very 
deeply rooted in our civilization, almost as deeply as our more com- 
mon seven-note scale. 

The question that naturally arises is: How did our musical scale 
develop and is there anything unique about it? If there were human 
beings on the planet Mars, for example, would they have developed 
the same scale we use or would it be something quite different? The 
answer is that they would probably have developed our modern musical 
scale, since it has a certain uniqueness that no other sequence of notes 
could have and is an attempt to 
fit a musical notation to the in- 
evitableness of arithmetic. 

This scale arose simultaneously 
in many parts of Europe and 
Asia over a period of some cen- 
turies and the sort of process 
taking place must have been 
identical in each locality. There 
seems to be hardly any doubt 
that the development was as 
follows: A pipe or string would 
be tuned to some note, say C on 
our keyboard. At the dawn of 
musical appreciation the octave 
was added, since it was early 
found that octave notes together 
give very pleasing concordance. Later, the 5th was added, that is, 
G, and we then had a three-note scale: C, G, C 1 . With the begin- 
ning of harmony it would soon be realized that whereas a single- 
note melody could be made using any desired interval between the 
notes, as soon as two melodies are combined the notes in the scale 
have to be adjusted so that the two parts sound well together. 

With a scale of C, G, C 1 , the next logical development would be to 
add a string or pipe that would sound as well with G as does C. This 
is again a 5th above G and is D on our scale. We now have four notes 
from which several harmonies can be obtained: CG, GD, CC 1 . A 
later development of harmony also accepted GC 1 although this prob- 
ably was not accepted at first. Another fifth above D gives A, and 
by following this process right up the scale, we find that the notes 
shown in Fig. 1 are obtained. Going up by a 5th twelve times brings 


FIG. 1. The twelve semitones of 
the 7-note scale. Each note has the 
ratio 2:3 with the note after it and 
the ratio 3:2 with the note before it 
(based on relation ( 3 A) 12 = 2 7 ). 

284 S. T. FISHER [j. s. M. P. E. 

us out again to our starting note C, seven octaves up. It is evident 
that when the early experimenters found they had again reached C 
they would consider that they had used all the natural notes and 
would be content with this scale of twelve tones. In other words, 
the modern musical scale is an inevitable result of the elementary 
equation in arithmetic: 

O N 

| ) ==2' (12 fifths = 7 octaves) 


129. 75 ==128 

The equality is not exact but is quite close. The residual interval is a 
quarter of a semitone, and is called the "comma of Pythagoras," 
Pythagoras having first pointed out the mathematical basis of the 
musical scale. A much more exact relation is that 


6 i = 2 31 

This would mean a 53-note octave, which is obviously too cumbersome 
for convenience. With the 12-note scale, if the inexactness of the 
basic relation is distributed over the twelve notes, we have a scale 
that obviously gives reasonably good concord and at the same time 
is fairly convenient, since only five additional notes have been put in 
to fill the gaps of our basic structure of seven notes. It is interesting 
to note that a 53-note scale was proposed by Mercator, the map- 
maker, about 1550, and about the year 1700 several organs were con- 
structed whose keyboard contained 53 keys to the octave. A subse- 
quent simplification was to reduce this to nineteen notes and the 19- 
note keyboard appears to have been adopted on quite a large scale 
during the Middle Ages. It is not, however, as exact as the 12-note 
scale. It will be noticed that the 5-note scale mentioned previously is 
obtained as any sequence of five fifths. While from the foregoing it 
is seen that a scale of twelve notes has been constructed, actually, 
according to a tradition going back possibly to 2000 B.C., a 7-note 
scale is used, the five additional notes being employed only as acci- 
dentals that is, for occasional effects or in order to permit music 
to be shifted in position on the keyboard that is, to be raised or 
lowered in pitch. Our 7-note scale is the scale that comes as second 
nature to everyone, whether he has any musical training or not; 
this is the familiar do, re, mi, fa, sol, la, ti, do. All music is written in 


this scale, which in the key of C is represented by the white notes on the 
piano keyboard. It is seen that this 7-note scale goes up by unequal 
increments and, if we adopt the usual musical language, the intervals 
between the notes in ascending order are tone, tone, semitone, tone, 
tone, tone, semitone. When the black keys are added as well, then 
all the intervals become semitones. 

A large number of scales have been constructed on the 7-note basis 
with five additional semitones in which the frequency intervals be- 
tween the notes have been arranged according to a number of rules 
so as to give the nearest approach to exact harmony. Most of these 
need not detain us; three, however, are of outstanding interest: 
those called the "mean- tone scale," "just scale," and the "equally 
tempered scale." From the time of Pythagoras it has been recognized 
that the mathematical basis of the musical scale is inexact and, 
Pythagoras having pointed out specifically that seven octaves are 
not quite equal to twelve fifths, a number of schemes have been de- 
vised in the intervening centuries to distribute this error in various 
ways over the scale. The mean-tone scale, proposed by the Greeks 
and used throughout the Middle Ages, was the first successful attempt 
to do this. In this scale the twelve ascending 5ths making up the 
seven octaves were each flattened slightly so that the final note was 
correct in either sequence. This scale was tolerable but suffered from 
the serious defect that the intervals that were noticeably inharmonious 
were those most generally used. In the mean-tone scale a tone was a 
frequency ratio of 9 :8, and a semitone, a ratio of 256 : 243 that is, the 
semitone was not half the tone: It will be seen what complication this 
leads to when it is desired to shift a piece of music upward or down- 
ward in the frequency spectrum, the operation the musician calls 
changing the key. When this is done in the mean-tone scale the 
harmony is badly disturbed, since the interval of a fifth, for example, 
can be expanded or compressed, depending on its position on the 
keyboard. Nevertheless, this scale was in use for many centuries and 
was used by the earlier of the great modern masters of music. On 
keyboard instruments where the tuning was fairly exact and where 
the harmony was complicated, it was very common for the musician 
to retune his instrument for the key in which the music was set. In 
orchestral instruments where the tuning is much less exact and the 
source of origin of the tones more diffuse, this was not done. The 
stringed instruments, the violin, the viola, the 'cello, and the double 
bass, do not employ frets on the strings, and as a result the exact into- 

286 S. T. FISHER tf. s. M. P. E. 

nation is continually under control of the performer, so that a violinist, 
for example, could play in the mean-tone scale and, when he changed 
key, readjust the intervals so that they would still be harmonious 
in the new key. Factors like these rendered the mean-tone scale satis- 
factory, even to the great musicians. 

About the year 1700, however, the modern scale began to be 
adopted. It had been known for many centuries and was probably in 
use in China in 1000 B.C. A complete description of it appears in 
Chinese manuscripts of 1500 A.D., including the mathematical re- 
lations involved. This scale was proposed and became adopted be- 
cause it has one great merit: it permits the player to shift from one 
key to another without any change in the intervals by which the scale 
progresses. There are twelve intervals in the musical scale and the 
equally tempered arrangement is this: that the frequency ratio of 
each note to the preceding one is the twelfth root of 2. It will be seen 
then that no matter what position on the keyboard a piece of music 
is set, the effect and the harmony are precisely the same, the only 
difference being an overall change in pitch. The equally tempered 
scale has one fortunate property, in that the interval of a fifth is 
almost exact. It is likely that one of the contributing causes toward 
the adoption of this scale was the fact that, when the development 
of the piano had progressed through the stages of spinet, harpsichord, 
clavichord, and all the others, to the modern form, the difficulty of 
retuning the instrument for each key, which is necessary on the mean- 
tone scale and without which the harmonies were sufficiently inac- 
curate to be intolerable, made it imperative to devise an arrangement 
in which this retuning was not necessary. 

The Greeks, although they had used the 7-note scale, had no such 
device as a change of key, since they did not employ harmony as we 
know it. They used, however, a change of mode, something that 
has almost disappeared from modern music. There were seven modes 
in Greek music and they were actually not simple changes in pitch 
of the whole of a piece of music but a change from one sequence of 
tones and semitones to another; in other words, there were seven 
different scales. Of these modes, two have remained: our major 
mode, which is the usual scale C, D, E, F, G, A, B, and, our minor 
mode which may, for example, be A, B, C, D, E, F, G. The Greeks 
attributed definite characteristics to each of their modes and this 
has been carried into our own music, so much so that the expression 
"in a minor key" is an accepted English phrase. 


Another thing that has been carried into modern musical thought 
from the modes of the Greeks and more recently the keys of the mean- 
tone scale, is the fiction that many musicians believe that different 
keys on the equally tempered scale have characteristic qualities. This 
simply is not so. A change of key in the equally tempered scale re- 
sults in nothing except a change of pitch. There is no change in the 
character of the music. This can be demonstrated beyond any ques- 
tion when it is pointed out that the key of F* major (6 sharps) uses 
the identical notes of the key of G b major (6 flats). Incidental effects 
do, however, exist. A violinist, unaccompanied, tends to play in 
true harmonic intervals; a change of key changes the number of 
strings that are played "open," i. e., at their maximum length. Some 
instruments have different qualities for different positions of playing, 
as the piano, and in some instruments some notes may be poor, as 
C* on the flute, and some notes may be unusually good, as high D on 
the same instrument. 

The Chinese musical scale of which mention has been made before, 
consists of our 12-note equally tempered scale, but the music has 
this fundamental difference: that all twelve notes are employed in 
any given piece of music that is, this music, as a musician would 
say, belongs in the chromatic scale. This scale was arrived at by 
the Chinese as an outcrop of their study of numerology and is pre- 
cisely correct. They took a bamboo flute tube of a given length and 
made up the scale by shortening the tube in twelve steps, the decre- 
ment in length of each step being a fixed proportion of the length of 
the preceding step. 

The equally tempered scale was not much used in England until 
about the year 1850 and was not generally used for some years after- 
ward. At the Exhibition of 1851, for example, it is said that not a 
single organ exhibited was in the equally tempered scale but that all 
were in the mean-tone scale. This seems to be rather a severe com- 
mentary on the English ear for harmony, since the equally tempered 
scale had been adopted generally in Europe one hundred and fifty 
years before, solely on the grounds that the mean-tone scale was in- 
tolerable except in the key of C. 

The other scale of fundamental interest in music is the just, or 
harmonic, scale. This is a theoretically correct scale but suffers from 
the disability that it can be played only in one key. It consists of a 
series of notes whose frequencies are represented by the numbers 1, 
Ys, 6 A> Vs, 3 A, Vs, 15 A, and 2. It will be seen that all these notes 



[J. S. M. P. E. 

bear simple numerical relations to the key note and therefore this 
scale is very rich in exact harmonies. Unfortunately there occur in 
it three different sizes of intervals, one having a ratio of 9/8, one 
having a ratio of 10/9, and one having a ratio of 15/16, so that at 
present no keyboard instrument is tuned to this scale. There seems 
very little doubt, however, that when a violinist is playing unaccom- 
panied by a keyboard instrument, he plays in this scale, and measure- 
ments made by Helmholtz and others indicate that this is so. In 
Table I is shown a comparison of the harmonic or just scale and the 
tempered scale intervals. This table shows two things: first, the 


Comparison of Harmonic and Tempered Scale Intervals 




Harmonic Scale: Harmonics of 




















































. . 












. . 











divergence of the tempered scale from a theoretically correct scale, 
and, second the excellence of the harmonies occurring in the harmonic 
scale between fundamentals and harmonics. In the tempered scale 
no such fortunate relations exist, since the fundamental intervals 
are all different from the theoretical values. The harmonics are more 
and more divergent in notes occurring higher on the keyboard as we 
go up in frequency. 

I have never heard a keyboard instrument played in the just scale 
but I think there is little doubt that it would give definitely a more 
pleasing effect than our usual tempered-scale instrument. This would 
be particularly true on the organ where extremely complicated 



harmonies both of fundamental and harmonics are obtained. Helm- 
holtz in 1860 commented on this and spoke of the extreme pleasure he 
got from playing a justly tuned instrument after playing on a tem- 
pered-scale piano. Of an organ tuned in the tempered scale he said, 
"When the mixture stops are played in full chords, a hellish row must 
ensue and organists must submit to their fate." We still submit to 
our fate. The just scale gives almost exact harmonies, but can not be 
played in more than one key without re tuning ; and the tempered scale 


Comparison of Scale of Equal Temperament with Hammond "Tempered Harmonic" 




Frequencies of Harmonics 
of Notes in Lower Octaves Which 
Appear in This Octave 

2nd, 4th, 8th 

3rd, 6th 



Natural pered 

Natural pered 

Natural pered 

Natural pered 



1000 1000 

1001 1000 

992 1000 

985 1000 



1059 1059 

1061 1059 

1051 1059 

1040 1059 



1125 1125 

1124 1125 

1114 1125 

1102 1125 



1189 1189 

1190 1189 

1180 1189 

1168 1189 



1260 1260 

1262 1260 

1250 1260 

1237 1260 



1335 1335 

1337 1335 

1324 1335 

1311 1335 



1414 1414 

1416 1414 

1406 1414 

1389 1414 



1498 1498 

1500 1498 

1486 1498 

1472 1498 



1587 1587 

1589 1587 

1575 1587 

1559 1587 



1682 1682 

1688 1682 

1669 1682 

1652 1682 



1782 1782 

1784 1782 

1767 1782 

1750 1782 



1888 1882 

1890 1882 

1875 1882 

1853 1882 



2000 2000 

2003 2000 

1984 2000 

1969 2000 

can be played in all keys, but what should be harmonious relations be- 
tween notes in the same octave are actually discords. From Table 
II can be seen an even more important source of discord, particu- 
larly noticeable, as it was to Helmholtz, in organs. This is the fact 
that the 3rd, 5th, 6th, 7th, 10th, and some of the higher harmonics 
of notes at the lower end of the keyboard do not duplicate notes on 
the upper end of the keyboard, but are noticeably out of tune with 
them. In the orchestra then, the 3rd, 5th, 6th, and 7th harmonics of 
the string basses must cause discord with the violins and woodwind; 
but the effect is not particularly noticeable, first, because we are used 
to it, second, because the instruments are all slightly out of tune in 

290 S. T. FISHER [J. S. M. P. E. 

various ways, and third, because the source of the discordant sounds is 
spread over a relatively large angle at the listener's ear. In the pipe- 
organ, the situation is definitely worse when the mixture stops are 
played. Mixture stops are those in which rows of pipes representing 
2nd, 3rd, 4th, and even up to the 10th harmonic are coupled to the 
fundamental pipes being played; so clash is inevitable between the 
natural harmonics of the fundamental notes, which in many cases 
are very strong, and these synthetic harmonics, which lie strictly 
in the tempered scale. In the piano, the discord between the nat- 
ural 7th harmonic and the tempered-scale notes was early recognized 
as disagreeable, and today all pianos are so arranged that the 7th 
harmonic is largely suppressed ; this is done also in organs and in the 
brass wind instruments. The oboe, among the orchestra instruments, 
is characterized by a strong 7th harmonic, and its harsh, penetrating 
quality may be largely due to the discords thereby produced. Two 
possibilities of remedying this situation theoretically are not open 
practically to the constructor of traditional musical instruments. The 
theoretical possibilities are : First, to supress all natural harmonics and 
use only tempered ones. This is obviously not possible practically, 
except to some extent in the case of the pipe-organ. Second, to shift 
to the just scale, so that in most important instances the natural 
harmonics appear almost exactly on the scale. This results in the 
limitation of the instrument to a single key. 

By far the best answer to date has been supplied by Laurens Ham- 
mond in his electric organ. In this instrument, musical qualities are 
synthesized from pure sine waves, and all the frequencies used in 
the synthesis lie on the tempered scale. In other words, natural har- 
monics are entirely suppressed and tempered harmonics substituted. 
In no other instrument, to my knowledge, is this done, and while 
the results are not immediately perceptible to the lay ear, the char- 
acteristically harmonious effect of the Hammond organ that becomes 
apparent after some familiarity with it must be ascribed to this basic 

A topic of great importance that we shall consider briefly is that of 
summation and difference tones. Communication engineers are 
familiar with the effect of superimposing two different frequencies 
and transmitting them through a non-linear network. We ordinarily 
say that side-bands are produced, consisting of sum and difference 
frequencies. The ear is non-linear to a marked extent, with the 
result that when two notes are sounded loudly, there become per- 


ceptible a number of other tones bearing related frequencies. The 
most prominent are the 2nd harmonics and the sum and difference 
frequencies of the two notes. It can be shown that if three tones repre- 
sented in frequency by the numbers 4, 5, and 6 are sounded, the hu- 
man ear will respond as if every frequency from 1 to 18 were present. 
It can be readily demonstrated with an organ, or for that matter 
with two oscillators, that if two tones of frequencies 2 and 3 are 
sounded together, a note of frequency 1 is plainly audible. This is 
the phenomenon that lets us hear the fundamental tones of a man's 
voice over the telephone, although these tones go down to 90 cycles 
and the telephone transmits little or nothing below 300 cycles. It 
lets us hear the low notes of the piano, down to 28 cycles, although 
acoustically most pianos are quite incapable of radiating a perceptible 
amount of power at these frequencies. This phenomenon, and par- 
ticularly the formation of difference tones, is very important in musi- 
cal instruments. In the pipe-organ where it is particularly notice- 
able, it is called "acoustic bass." The summation tones, especially, 
give rise to serious discords. Suppose we have a note sounded with 
strong 3rd and 4th harmonics. The difference tone of the harmonics 
is simply a strengthened fundamental, but the summation tone is 
the 7th harmonic, which is extremely discordant in the tempered scale. 
In the case of drums, bells, and other instruments in which the par- 
tials are not harmonics, difference tones can not be relied on to supply 
a bass that is not transmitted. 

Musical tones, being sounds, are always produced by vibrating 
mechanical systems, capable of acoustic radiation. The piano, the 
violin, the pipe-organ, or the human voice are examples in which the 
radiating element is actuated mechanically. In all these instances, 
the further feature exists that the radiating element is also the gen- 
erator. We can conceive of a variety of ways in which a piano, for 
example, could be modified by the application of electricity. The 
striking mechanism could be actuated by electromagnets instead of 
directly by the performer; the strings could be sounded by a micro- 
phone-hummer arrangement; the strings could be enclosed and the 
sound picked up by a microphone and reproduced through an ampli- 
fier and loud speaker; or instead of a microphone, a direct electro- 
magnetic or electrostatic coupling to the strings could be used. While 
all these schemes and combinations involve electricity in the produc- 
tion of musical tones, we are most concerned with the case in which 
an electric current of the required character is generated; and when 

292 S. T. FISHER [j. s. M. P. E. 

this current, after amplification, is passed through a loud speaker, a 
musical tone is produced. 

There are two fundamentally different ways in which such an elec- 
tronic instrument may be arranged to produce musical tones: The 
tone can be generated in the first instance as a complete wave of the 
desired character, which is then amplified and reproduced; or it can 
be produced as the addition of a group of sine- wave frequencies lying 
in a harmonic series. 

In the Hammond organ the latter arrangement is used. The tone- 
generator consists of ninety-one miniature tone- wheels. These wheels 
are made of steel, and each has a sine wave cut in the periphery. 
A single permanent-magnet pole-piece with a coil wound on it is used 
with each generator. All the generators are driven from a single 
synchronous motor with elaborate precautions taken to prevent fre- 
quency-modulation flutter. These consist of a damped low-pass 
mechanical filter in the main drive, and of a similar small section in 
the drive to each pair of tone- wheels. The generator assembly con- 
sists of two groups of jack shafts, on each of which is mounted two 
tone-wheels, separated in frequency by an integral number of octaves, 
and a gear and mechanical low-pass filter. These two groups are driven 
by gears mounted on a main drive-shaft and one group lies on each 
side of it. It is evident that the limitations of motor speed, and of 
cutting whole numbers of teeth on gears and tone- wheels, will not per- 
mit an exactly precise duplication of the tempered scale. Com- 
promises have been necessary, but they are of negligible importance. 
This could not be said of such departures from the just scale, if it 
were in use instead of the equally tempered scale. Note this point, 
however: if the just scale were used for this organ, no departures 
would be necessary, since all the frequencies bear simple fractional 
relations to each other. In the Hammond organ, the octave intervals 
are maintained precisely, this being the purpose of the small jack 
shafts, each with two tone-wheels mounted on it. 

The output of each pick-up coil is passed through a low-pass filter 
to reduce it as nearly as possible to a sine wave. In this instrument, 
provision is made to synthesize tones using a fundamental or 1st 
harmonic, the 2nd, 3rd, 4th, 5th, 6th, and 8th harmonics; the sub- 
harmonic, or octave below the fundamental; and the sub-third, a 
fifth above the fundamental. From these nine partials pipe-organ 
voices can be imitated, in some cases perfectly, in all cases adequately, 
and this is true of most of the orchestra instruments. Obviously, 


tones can be set up that are entirely new qualities, not produced by 
traditional instruments. It is evident that each generator output 
appears in a number of places on the keyboard. For instance, if we 
have a generator that is the fundamental frequency of Middle C, it is 
the 2nd harmonic of the C below, the 4th harmonic of the C below 
that, and the 8th harmonic of the C below that again. It is the sub- 
harmonic of the C above, the 3rd harmonic of the F an octave and a 
fifth below, and the 6th harmonic of the F two octaves and a fifth 
below. It is the sub-third harmonic of the F below and the 5th har- 
monic of the G # two octaves and a third below. 

Since a tone produced by the organ may include all nine partials, 
each key carries an assembly of nine contact springs. The moving 
sides of these contacts connect to the generators, the stationary sides 
through the switching mechanism that selects the desired harmonics 
and adjusts their relative strengths to an amplifier contained in the 
console. The output from this amplifier is fed to as many power- 
amplifier tone-cabinet units as may be necessary. 

The relative amplitudes of the generator outputs are adjusted by 
sliding the pole-pieces. The output is adjusted to a curve rising 
steeply from the high-frequency end to the low-frequency end. Aside 
from the harmonic-suppression filters on each generator, no electrical 
filters are used. From the previous discussion of the tempered scale, 
it will be realized that the suppression of natural harmonics is of the 
greatest importance except in the top octave of the keyboard, where 
they fall outside the range of any of the generator fundamental fre- 
quencies. Accordingly no harmonic filters are employed on the top 
octave of generators, to permit the added brilliance of an extended 
harmonic range. 

The strength of each harmonic in a tone can be set in eight steps 
of 3 db. each, or cut out entirely. Controls are provided so that four 
tones can be set up, two for each manual or keyboard, and can be 
brought in by pressing a button. In addition, a limited range of 
tones can be set for the pedals. Eighteen of the usual pipe-organ 
qualities are permanently adjusted, and nine may be used on each 
manual by pressing the appropriate switches at the left of the key- 
board. The volume-control, operated by a foot-pedal, has a total 
range of 30 db. 

A tremulant is provided by a motor-driven potentiometer, and the 
effect is variable by means of a manually operated potentiometer 
connected across it. An effect of great importance that is provided 

294 S. T. FISHER [j. s. M. P. E. 

is the so-called "chorus effect." It is this that enables us to tell twenty 
violins playing in unison from one violin playing loudly, and is par- 
ticularly noticeable in the pipe-organ, where frequently a great num- 
ber of pipes of the same pitch may be sounded together. With a 
number of separate sources, it is inevitable that small frequency differ- 
ences should occur and this, together with random and changing 
phase relations, is imitated in Hammond's organ by having, for 
each generator representing a keyboard note, another generator 
slightly out of tune with it, whose output is quite low. This second 
set of generators can be connected at will by a control at the right 
of the keyboard. 

The Hammond organ is widely accepted by musicians and is now 
in general use throughout the world. Among other electronic instru- 
ments that have been commercially exploited is the Everett Orgatron, 
an instrument that employs wind-blown reeds with electrostatic pick- 
ups. The reeds are in a sound-proof chamber, and different tone 
qualities are obtained by using different banks of reeds and by shap- 
ing the response curve of the amplifier. This instrument gives the 
characteristic reed-organ quality. There are several pianos with 
electrostatic or electromagnetic pick-ups on the strings that are 
said to be extremely effective, since they permit the elimination of 
the sounding board, the bass can be enhanced at will, and a wide 
volume range can be obtained without the necessity of tremendous 
exertion by the performer or of changing the quality of the sound 

A number of organs using vacuum-tube oscillators have been pro- 
duced commercially, some using a separate oscillator for each note, 
some using only twelve oscillators, one for each note in the lowest oc- 
tave, all the upper notes being obtained as harmonics. There appear 
to be two objections to these instruments : first, the large number 
of vacuum-tubes involved in the hundreds and second, the diffi- 
culty of keeping them exactly in tune. These problems are undoubt- 
edly capable of solution, however. 

An outstanding example of the principle of the generation directly 
of a complex tone, instead of synthesis from harmonic components, 
is the Robb Wave-Organ, designed by Morse Robb and constructed 
at Belleville, Ontario. This interesting and successful instrument 
consists of a console connected by a multi-conductor cable to the tone- 
generating unit, and the usual amplifiers and loud speakers. The 
generator consists of twelve spindles, one for each note in the octave, 


each with a number of disks, and driven through belts and pulleys 
from a single motor. On these disks are cut the complex wave-forms 
it is desired to reproduce, so that, subject only to the limitations of 
the amplifier and loud speaker equipment, almost any tone can be 
accurately reproduced. A very large number of generator disks is 
required one for each keyboard note, for each tone color. The total 
number is substantially reduced, however, by using generators in 
the form of cylinders, not flat disks; a number of pick-ups are em- 
ployed on each cylinder, at different points in the height of the wave- 
form, and different pick-ups and different combinations of pick-ups 
give wide variations in tone-quality. This organ is provided with a 
group of standard pipe-organ stops, the disks being cut from oscillo- 
grams made from an acoustic pick-up from a pipe-organ. The Robb 
Wave-Organ embodies a number of ingenious points in its design and 
must be regarded as a serious musical instrument. 

The classical work on electrical musical instruments was carried 
out by Thaddeus Cahill, between the years 1895 and 1905. All 
the modern inventors have drawn largely on his work, which is ex- 
plained and described exhaustively in five patent applications drawn 
up by him. Cahill appears to have been the first man to conceive 
the idea of the electrical production of musical tones. He produced 
several models of an instrument which he called the Telharmonium. 
To ship one of these instruments from his laboratory at Holyoke, 
Mass., to New York required forty railway cars; the instrument 
weighed over 200 tons and cost upward of a quarter of a million dol- 
lars! Cahill intended to use his Telharmonium to transmit music 
over telephone lines to subscribers; the plan finally fell through be- 
cause of cross-talk into adjacent circuits. 

Cahill clearly understood all the theoretical and practical problems 
involved in the electric organ; he outlines them in great detail, to- 
gether with the extraordinarily ingenious features of his Telharmo- 
nium. Since, of course, he had neither vacuum-tube amplifiers nor 
modern loud speakers, he had to generate relatively great amounts of 
power. He employed generators in the form of wound-rotor alterna- 
tors, commutators (he used the word "rheo tomes") and vibrators. 
The bed-plate of his main generator assembly was sixty feet long. He 
understood and used low-pass and band-pass filters and matching net- 
works of many configurations, and understood the impedance rela- 
tions of his circuits and the importance of satisfactory transient char- 
acteristics, all these at a time when such knowledge was not general 

296 S. T. FISHER [j. s. M. P. E. 

in any branch of communication engineering. Initially he used great 
multiple loud speakers made of vibrating magnets clamped to hard- 
wood bars; later he used telephone receivers with conical horns. His 
Telharmonium provided much more complete facilities to the per- 
former than has any electrical or acoustic organ before or since. He 
employed the methods both of tone synthesis from pure tones, and of 
the generation of complex tones. An article in 1906 in The Electrician 
describes the performance of the Telharmonium : 

It is evident that the constructional features of the electrical mechanism are 
exceedingly elaborate. It is believed, however, that the results obtained fully 
justify the means employed. There can be no doubt as to the absolute accuracy 
of the relative pitches of the various notes produced, nor as to the beauty and 
purity of the resultant music. Although the horn of the receiver resembles that 
of a phonograph, there is nothing about the music itself to suggest the phonograph, 
the harsh sounds and disagreeable overtones of which are entirely lacking. The 
quality of the sound is pure and sweet and the volume is such that the largest 
known auditorium can be served without the use of an excessive number of re- 
ceivers, while the character and expression of the music is under the control of 
the musician to an extent not previously reached in any musical instrument. 

The question will naturally arise in the mind of the reader as to the practical 
use of this complicated and expensive apparatus. The plans of the inventor are 
to distribute music from a central station to hotels, restaurants, theaters, and 
private homes. The remarkable purity and strength of the sounds produced 
electrically, enabling a few performers at a central station to produce orchestral 
music at a thousand places, strikes the imagination and it seems not improbable 
that at no distant day orchestral music for the dinner table will be as common in 
the homes of the people as it is now in the great hotels. Music of different sorts 
during the evening, and slumber music during the small hours of the night com- 
ing to the listener by electricity from a central station, seem likely in a few months 
to be accomplished facts in one or more American cities. 

The design of the transmission circuits of an electrical organ such 
as the Hammond presents a number of problems. The frequency 
range is from 32 to above 8000 cycles, and the maximum output oc- 
curs at the lowest frequency. This involves the design of amplifiers 
and loud speakers whose efficiency and power-handling capacity are 
unimpaired at 32 cycles. From the discussion of the tempered scale, 
it will be realized that the suppression of natural harmonics in the 
amplifier-loud speaker system is of the greatest importance. This 
requires careful design of the amplifier, and of the acoustic loading on 
the loud speaker so that even at the lowest frequencies no break- 
up occurs. 

Another point largely ignored in ordinary transmission systems, of 
great importance in a system for the transmission of organ tones 



is that in a wave made up of a harmonic series with random phase 
relations, the peak value of the wave reaches a relatively high value 
for a given rms. value. In other words, the power output capacity 
of the amplifier is largely reduced due to the wave-form of the tone 
being transmitted. Fig. 2 shows the magnitude of this effect. 

What significance can engineers draw from the facts that have been 
presented? What of the future development of the instrumentalities 
of music ? One possibility that is of overwhelming importance now ap- 
pears: that is, to abandon the tempered scale in favor of the just 
scale. It has been seen what inaccuracies of harmony are inherent 



O c 



s * 







s 4 ft % r i 6 m to 


FIG. 2. Decrease of maximum output of amplifiers 
for wave-form consisting of equal harmonic components. 

in the tempered scale. Its main virtue is its convenience, the fa- 
cility it provides for changing key. The just scale must be retuned 
for each key, but is the ideal solution to the 7-note scale since it pro- 
vides the largest number of exact harmonies possible. This makes its 
use impossible in the traditional keyboard instruments. The stringed 
instruments in the orchestra can readily play the just scale in any 
key, since the pitch can be continuously varied ; the wind instruments 
can also, by means of changing the length of the air column with tele- 
scoping joints for small changes of pitch and by using different instru- 
ments for large changes. With the advent of electrical keyboard 
instruments a new era in music is initiated. It is now possible to tune 
such an instrument in the just scale, and to change key electrically 
by altering the frequency of the generating devices. The implica- 
tions are too broad to be touched upon in this paper, but from 
what has been said it will be apparent that the resulting improve- 
ment in the harmoniousness of our music would be large. 


Summary. The recent advances in color photography have made more apparent 
than ever before the need for some simple and accurate method for the estimation of 
the color -temperature of light-sources. Photographers, whether professional or ama- 
teur, are only too well aware of the influence which the quality of the illumination has 
on the color rendering of photographic subjects. For example, the difference in color- 
temperature between general-purpose tungsten filament lamps, and studio modeling 
lamps, or between modeling lamps and photoflood lamps, is often the deciding factor 
between correct and incorrect photographic color reproduction. In order that the 
photographer may easily determine the quality of lighting which he is using and make 
the proper adjustments to secure standard lighting conditions, an instrument that is 
at once compact, simple in operation, and accurate, has been developed in these 
laboratories. No auxiliary light-source is required for making measurements since 
each source is tested by means of the radiant energy which it itself emits. In this 
paper a discussion of the principles applied in construction of the instrument, a de- 
scription of the instrument, and data showing the probable error of results are given. 

The recent advances in color photography have made more appar- 
ent than ever before the need for some simple and accurate method 
for determining the characteristics of light-sources. If the spectrum 
of a source such as a tungsten lamp is examined and the relative 
energy of light of each wavelength determined and plotted against 
the wavelength, a graph will be obtained known as a spectral energy 
distribution curve. Fig. 1 is such a graph for a 100-watt tungsten 
lamp. It has been found that the spectral distribution of energy 
throughout the spectrum of an incandescent solid, for example, the 
filament of a tungsten lamp, is practically independent of the material 
of which it is composed and is dependent only upon the temperature. 
As the temperature of an incandescent solid is raised, the wave- 
length at which the maximum energy is emitted moves from the 
long toward the short-wave region of the spectrum. This shift 
of the maximum with temperature, illustrated in Table I, gives rise 

*Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 28, 
1938. Communication No. 698 from the Kodak Research Laboratories. 
**Eastman Kodak Company, Rochester, N. Y. 




to the common experience that as the glowing material becomes 
hotter it appears whiter. Since the most efficient thermal radiator 
is a completely black body, the energy distribution may be said to 
correspond to that of a "black body" at a given temperature. The 


FIG. 1. Graph showing relative spec- 
tral distribution of energy for a 100-watt 
tungsten lamp. 

temperature is measured from the absolute zero on the Centigrade 
scale stated as K (degrees Kelvin) and is called the "color"-tempera- 
ture, for our purpose, color-temperature may then be defined as 
the temperature at which a complete radiator (black body) will 
match in color that of the source in question.* 


Table Showing the Wavelength of Maximum Energy at Various Color-Temperatures 
Color Temperature (K) Wavelength of Maximum Energy (m/*) 

1000 2880 

2000 1440 

2500 1152 

3000 960 

3500 823 

4000 720 

6000 480 

8000 360 

10000 288 

*A more precise definition is: "The color-temperature of a radiator (source, 
lamp) is the temperature at which a complete radiator must be operated in order 
to emit energy competent to evoke a color of the same chromaticity as the color 
evoked by the radiant energy from the source in question." 1 



[J. S. M. P. E. 

Photographers, whether professional or amateur, are only too 
well aware of the influence which the quality of the illumination has 
on the color rendering of photographic subjects. That is to say, 
the distribution of energy from the source of light used is extremely 
important in its effect upon the appearance of objects which it 
illuminates. Everyone is familiar with the phenomena of color 
change brought about in many objects when examined under different 
light sources. The difference in color-temperature between general- 
purpose tungsten lamps, and studio modeling lamps or between 
modeling lamps and photoflood lamps may well be the deciding 
factor between correct and incorrect photographic color reproduc- 
tion. Variations in the voltage applied to a given lamp, or the length 








FIG. 2. Diagram showing spectral regions used in the 
color temperature meter. 

of time it has been in operation are by no means negligible factors in 
securing and maintaining proper lighting. 

In order that the photographer may easily determine the quality 
of lighting which he is using and make suitable adjustments to secure 
standard lighting conditions, an instrument for that purpose, which 
is at once compact, simple in operation, and accurate, has been 
developed in the Kodak Research Laboratories. 

In working out the design of the color-temperature meter, use was 
made of some of the well known principles of color and color mixture. 
Suppose that in some way we block out or absorb certain components 
of the light from an incandescent source as represented by the shaded 
areas in Fig. 2 (B). We have left narrow bands in the green and red 
which, if combined, will produce a visual impression of yellow or 
orange. This orange will appear to the eye as though the shaded 


areas in Fig. 2 (C) had been removed and only a single narrow strip 
allowed to pass. In other words, a mixture of a properly selected 
narrow band of wavelengths from the green region with another from 
the red will produce the same visual impression as that of a single 
small group in the yellow-orange portion of the continuous spectrum. 

In the Kodak color-temperature meter the selection of the proper 
portions of the spectrum is accomplished by means of carefully con- 
structed light niters. One of these niters is so made up that it 
possesses two transmission bands with maximum transmittance at 
about 520 mju and at 680 mju, respectively. The second filter is so 
composed that the wavelength of its maximum transmittance is at 
approximately 580 mju. The relative transmittances of the bands in 
the two-band or dichroic filter are so adjusted that, when examined 
by light, for example, that from a tungsten lamp operating at a color 
temperature of 2100K, its color will be the same as that of the filter 
with its maximum transmittance at 580 m^u. For color-temperatures 
higher than 2100K, the dichroic filter will appear more green than 
the monochromatic one, while for temperatures lower than 2100K, 
it will appear more red. This property of dichroic materials was 
shown by Pfliiger 2 in his work on anomalous dispersion and was 
discussed by Wood in his Physical Optics* 

The reason for this behavior may be explained by reference to Fig. 
3. Curve A represents the spectrophotometric transmission curve 
of the two-band filter which has two maxima, at 520 m^c and at 680 
mju, respectively. Curve B is that of the monochromatic filter 
which possesses a transmittance maximum at 580 m/x. As stated 
above, the relative transmittances of the two bands for filter A have 
been so adjusted that, when examined by light from a source operat- 
ing at a color temperature of 2100K, this filter will appear to be the 
same color as filter B. The curve labeled 2100K represents the 
relative energy emitted at the various wavelengths of the visible 
spectrum by the source operating at 2100 K, which is the tempera- 
ture at which the filters will be color-matched. A source working 
at a color- temperature of 3200 K will emit energy of somewhat 
different distribution at the various wavelengths. Examination of 
the two distribution curves shows that the energy emitted is relatively 
higher at 520 m/u and relatively less at 680 m/x for 3200K than for 
the 2100K source. This will result in more light passing through 
the 520 rnju band in A and less at 680 m/x, and there will be a change 
in the color of the filter such that it will appear more green than 



[J. S. M. P. E. 

when examined with the 2100K source. In the case of filter B, 
however, there will be relatively little change in hue and it will still 
be yellow. If the color-temperature of the source is reduced below 
2100K, for example, to 2000K, the filter A will appear more red 
than B because the ratio of energies in the regions of the spectrum at 
the positions of maximum transmittance of the filters has changed 
so that there is relatively more energy in the red portion than at the 
original match point, namely, at 2100K. 

TOO eoo 


FIG. 3. Spectrophotometric transmittance 
curves of field niters used in color-temperature 
meter and relative energy distributions for color- 
temperatures of 2100K, 3200K, and 5000K. 

In order that the two filters shall remain color-matched when the 
color- temperature of the source is other than 2100K, it is necessary 
to modify the energy distribution of the source in some way. This 
modification may be accomplished by changing the voltage applied 
to the lamp until its color-temperature is once more that of the 
original. The necessary change in voltage may be used as a measure 
of the difference from 2100K. Another method of accomplishing 
the desired result is to absorb a portion of the radiant energy selec- 
tively with respect to wavelength in such a way that the remainder 
matches that at the initial temperature. Filters of this type, such as 
the so-called daylight glasses or the Wratten Photometric Series of 

Mar., 1939] 



filters, are well known. In the present instance, we are interested 
in reducing the color-temperature, since the match point for the filters 
is lower than that of most practical light-sources, and we require an 
amber colored filter. This amber filter is made up in the form of a 
wedge and the amount of selective absorption is dependent upon the 
thickness of the wedge at any point. The greater the thickness of 
the portion of the wedge used, the greater is the reduction in color- 
temperature of the light transmitted. 

In the color-temperature meter, the principles just described have 
been applied as illustrated in Fig. 4. A circular photometric field P, 
with a fine dividing line across the center, is formed by the narrow 
band-filters whose absorption characteristics are illustrated in Fig. 3. 






FIG. 4. Illustrative 


of color-temperature 

The left half of the field, which is shown in detail at-B, is formed by the 
dichroic filter, and the right half is formed by the monochromatic one. 
Between the eyepiece lens E and the test field is an amber wedge W, 
for the purpose of modifying the energy distribution of the light 
from the source being examined. This wedge is circular and the 
portion of the wedge to be used is selected by means of a small 
knurled knob K. The scale of the instrument 5 is so calibrated that 
it reads directly the color-temperature of the source investigated. 

Fig. 5 is a photograph of the instrument depicting both front and 
side views. Comparison of the reproduction of the meter with the 
six-inch rule at the bottom of the picture illustrates the compactness 
and convenient size of the design. 

Actual operation of the meter is accomplished by the observer 
directing the visual axis of the instrument (dotted line in Fig. 4) 
toward the source in question. He then observes whether the two 



[J. S. M. P. E. 

halves of the field of view are color-matched and, if they are not, 
adjusts the position of the wedge until such a color-match is obtained. 
A clockwise motion of the wedge increases the amount of absorption 
while a counterclockwise motion decreases it. The farther the 
wedge must be inserted, the higher is the corresponding color-tem- 
perature as read from the scale. 

Because of the fact that there are certain slight differences between 
the eyes of different individuals, the dichroic and monochromatic 
filters are not always color-matched at the same color temperature. 
For this reason, some means of compensation must be provided if 
determinations made with the instrument are to be in satisfactory 

FIG. 5. Photograph of color-temperature meter. 

agreement for two or more observers. To overcome this difficulty, 
an accommodation scale has been provided which enables each in- 
dividual to select the initial setting of the amber wedge which suits 
his particular eye. Before making any measurements, each ob- 
server must set the scale of the instrument at the value corresponding 
to a source of known color-temperature. A tungsten lamp which 
has been calibrated properly would serve admirably for this purpose 
but, since such a lamp must be operated at constant voltage, auxiliary 
equipment is required which is not always available. Beeswax 
candles, such as, for example, the XX,X Superior Candles made by 
the Socony Vacuum Oil Company, are easily obtained, and, since 
they possess fairly uniform temperature characteristics (1935K =*= 
10), they are quite suitable for the purpose of adjusting the accom- 


modation scale, when used with the auxiliary blue filter. This 
filter, which raises the color-temperature of the candle-flame to a 
point above 2100K is supplied in an easily attached mount. 

To make the initial adjustment, the operator first sets the point 
on the scale marked C opposite the index. Then, while applying 
pressure to the scale with the thumb of one hand, to prevent any 
displacement of the scale relative to the index, he rotates the knob 
with the other hand until a color-match is obtained in the field of 
view. During this operation, the candle-flame is the illuminant. 
After the preliminary adjustment, the meter is in condition for read- 
ing the color-temperature of some unknown source. 


Table Showing Precision of Measurements with the Color-Temperature Meter 

Average Departure from 
Observer Temperature K Mean of 10 Settings 

EML 2360 14 

AS 2360 24 

KSW 2360 15 

EML 2660 15 

AS 2660 30 

KSW 2660 22 

EML 2850 22 

AS 2850 26 

KSW 2850 28 

EML 3200 21 

AS 3200 35 

KSW 3200 34 

The precision of the measurements made with the color tempera- 
ture meter depends upon certain fundamental requirements. In the 
first place, the operation of the instrument is based upon the ability 
of an observer to do color-matching and therefore assumes his color 
vision to be normal ; that is, he must not be color-blind or have any 
noticeable deficiencies in color vision. In the use of the meter, as 
in all operations requiring the application of optical instruments, the 
precision of setting is considerably improved by practice. The first 
few attempts to balance the field by an individual unskilled in this 
type of measurement are likely to show very erratic results, but as 
he becomes accustomed to the manipulations necessary, his repeat- 
ability will improve and his results will be quite satisfactory. 


In Table II are shown the average deviations from the mean of 
ten settings made by each of three observers at the color temperatures 

A number of devices embodying somewhat the same principles as 
those applied in the Kodak color temperature meter have been 
developed over a period of years. 4 ' 5 ' 6 ' 7 Among them is the Harrison 
color meter, manufactured by Harrison and Harrison, Hollywood, 
Calif., which appeared on the market several years ago. This 
instrument is said to be useful for selecting the proper compensating 
filter, several of which are supplied with the instrument, to be used 
over the camera lens in order that the quality of light reaching the 
film may be properly adjusted to give correct color rendering. In 
the Harrison meter, rotation of a dial causes the field of view to change 
from a blue through a pink to a deep magenta. A setting for the 
selection of the correct filter is based upon the ability of the operator 
to decide when the field "just turns pink." 

Another appliance is that described in U. S. Patent 1,865,878, 
issued to Gerhard Naeser and assigned to the Kaiser Wilhelm Insti- 
tute in Germany. The Kodak color temperature meter possesses 
the advantage of providing automatic control of the brightness 
match in the field of view, whereas in the Naeser instrument, the 
brightness, if matched at one color-temperature, will not match at 
any other. The Kodak meter has a further advantage not provided 
by Naeser's arrangement. This is that the hue in the two halves of 
the photometric field matches at all temperatures within the range 
of the instrument while that of Naeser does not. 

It is the opinion of the authors that the instrument described in 
this paper provides a means whereby the photographer may easily 
and accurately estimate the color- temperature of his light-sources. 


1 PRIEST, I. G.: J. Opt. Soc. Amer., 23 (1933), p. 41. 

2 PFLUGER, A.: Ann. der Physik und Chem., 46 (1895), p. 412; 58 (1896), p. 

3 WOOD, R. W.: "Physical Optics," p. 438 (1911). 

4 Soci6t6 Arnoux, V ve Chauvin et Cie, French Pat. 734,726. 

5 Siemens & Halske A.-G., Austrian Pat. 75,291. 
8 Siemens & Halske A.-G., French Pat. 715,580. 

7 Naeser, G., assigned to Kaiser Wilhelm Inst., Germany. U. S. Pat. 1,865,878. 



Summary. The maintenance of developer activity over a long period of time is 
among the most important problems of a motion picture laboratory. The developer 
is oxidized by the silver halide in the emulsion and by air. When known amounts of 
these two oxidizing materials react with the developer, simple calculations (presented 
in a previous paper) are sufficient to determine the equilibrium condition of the de- 
veloper as well as the replenisher formula to give a chosen equilibrium. Under 
ordinary conditions there are large variations in the amount of developer oxidation. 
A chemical analysis immediately detects any deviation from the correct equilibrium 
and permits readjustment of the replenisher formula. Chemical analyses are pre- 
sented which require a minimum of equipment and time. In most cases ease of 
manipulation and speed have been considered as more important factors than a high 
degree of accuracy but in all cases the methods are capable of giving results to an ac- 
curacy of five per cent or better. Whenever possible the analyses are colorimetric in 
nature, the measurements being made on an instrument called an opacimeter. One 
operator can make a complete analysis in about half an hour. Analysis for any one 
constituent may be made in a much shorter time. It is emphasized that no one control 
variable is significant for specifying the activity of a developer. Sensitometric curves 
are included demonstrating the time lag in pH equilibrium but not in photographic 
equilibrium when hydroxide is added to or released in the developer. The aim of 
chemical control is to insure a constant condition of the developer and thus constant 
photographic quality, rather than to determine the degree of development. 

In the continuous processing of motion picture film the developer 
can not be fresh for each roll of film but must be used continuously. 
For this reason the developer must be kept at constant activity by 
continuous addition of fresh developer and removal of old. The 
problems of keeping this developer at the correct activity and of 
determing whether it is at the correct activity are among the most 
important problems which confront a motion picture laboratory. 

During the use of a developer solution, some of it is oxidized by the 
film being developed and some by air. If each of these reactions is 
taking place at a constant rate and the developer is being replenished 

*Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 28, 
1938. Communication No. 696 from the Kodak Research Laboratories. 
**Eastman Kodak Company, Rochester, N. Y. 


308 R. M. EVANS AND W. T. HANSON, JR. [j. s. M. p. E. 

at a constant rate, the concentrations of the ingredients of the solu- 
tion, both those added in the replenisher and those formed by the 
reactions, will reach an equilibrium concentration. These equilibrium 
concentrations can be calculated easily by means of equations pre- 
sented by the senior author in a previous paper. l From similar cal- 
culations, it is possible to determine the formula and rate of addition 
of a replenisher which will give almost any desired equilibrium condi- 
tion. Consequently, if the relative ratio of silver halide development 
and oxidation by air can be kept constant, the developer solution can 
be brought to the correct condition with ease and will remain in this 
condition. The resulting photographic quality will be correct and 

The problem is not quite as simple as this, however. A 1000-ft. 
roll of motion picture positive film contains about 75 to 80 grams of 
silver bromide and, depending on the type of scenes included on such 
a roll, 5 to 60 per cent of it may be developed. At other times it 
may be necessary to run leader rather than exposed film through the 
machine. In addition to the variation in the amount of silver 
bromide which is developed in a given time, there will be variations 
in the amount of aeration of the developer. A small amount of air 
is always carried into the developer by the film and by general surface 
agitation, but this amount of aeration may be increased suddenly to 
10 to 15 times its original value by a leak in the pumping system. 
Even after a few days of continuous processing, these inconsistencies 
make it impossible to know the concentration of the important in- 
gredients of a developer solution without the aid of chemical analyses. 
An analysis of such a partially exhausted developer immediately 
detects any deviation from the proper equilibrium condition and a 
new and correct replenisher formula can be calculated and put into 
use. By frequent analysis and replenisher correction, accurate 
developer maintenance can be accomplished. 

The number of analyses necessary for such developer maintenance 
is relatively small compared with the total number of constituents 
of a partially exhausted developer solution because many of the 
materials formed during the oxidation of the developer are inter- 
related and are formed in amounts which have a constant ratio to 
each other. For example, in an ordinary MQ developer, the amount 
of bromide formed is related to the amount of elon used up, the 
amount of sulfate formed is proportional to the amount of oxygen 
which the solution has absorbed from the air, which in turn is almost 


proportional to the hydroquinone which is used up. In addition, 
most of the oxidation products of the developer solution play an 
insignificant part in the development process (excepting bromide 
and acid or alkali) and need not be determined. 

In the case of an ordinary MQ developer, the most important 
variables are elon, hydroquinone, bromide, sulfite, alkaline salts, 
and pH. Analyses for these will tell the general condition of the 
bath and indicate what changes in the replenisher are necessary. 
In certain special cases, there may be other important ingredients 
which should be determined, but such cases are rare. The usual 
case does not even require repeated analyses for all of the materials 
mentioned above. Frequent checks of two or three of these vari- 
ables, alternating so that no one is omitted for a long period will give 
sufficient information to enable correct developer maintenance. In 
this way, the problem of developer maintenance can be made rela- 
tively simple. 

If attempts are made to carry the simplification too far, the value 
of analytical methods may be destroyed. The action of a developer 
compound is affected by a large number of variables which are by 
no means independent. In fact, it is safe to say that there is no 
single variable which may be used alone to control a photographic 
developer. The action of all developers is normally a steep function 
of pR and bromide concentration and even at a given pH, different 
developers behave so differently that no developer formula can be 
devised which may be specified by a knowledge of one of the con- 
stituents. In an earlier paper 2 the authors showed that pH, which 
has at times been considered as a significant single variable, may 
vary in the opposite direction to the developing properties of a given 
solution. Another example of the lack of correlation between pH. 
and developer action is shown in Fig. 1. The curves in (a) were 
obtained from sensitometric strips of motion picture positive de- 
veloped in fresh D16 developer. The H of this solution was 9.9. 
To a liter of this solution 2 grams of sodium hydroxide were added 
and more strips were developed immediately (curves b). The pH 
at this time was 10.1 and the activity of the developer had increased 
appreciably, as may be seen by a comparison of (a) and (b). After 
this solution had stood for 7 hours, strips (c) were developed and the 
pH. was found to be 10.3. A comparison of (b) and (c) will show that 
the photographic action of the developer had not changed at all, 
while its pH had changed 0.2 units. Hydroxide and acid are released 


R. M. EVANS AND W. T. HANSON, JR. [J. S. M. P. E. 

continuously during the use of a bath. The above test shows that 
hydroxide comes to an immediate photographic equilibrium with 
the bath but that this equilibrium does not have its full effect on the 
pH of the solution for several hours. Under these conditions a 
measurement of ^>H is not even significant as a measure of the re- 
leased hydroxide when it is measured during the use of the bath. 

On the other hand, as complete a chemical analysis of a developer 
as is possible at the present time will not specify its exact photo- 
graphic properties. Traces of materials, such as sulfide, which may 
be formed in the solution by bacteria, will cause fog even if present 
in quantities much too small to be detected by any available analyti- 
cal methods. Small traces of certain materials, such as hypo or 


FIG. 1. Sensitometric curves of strips of motion picture positive film 
developed (a) in D16; (b) in D16 plus sodium hydroxide; (c) same as (6) 
after standing 7 hours. 

iodide, may accelerate development. On the other hand, certain 
decomposition products of gelatin may act as inhibitors, slow down 
development, and decrease fog. Many other materials may inad- 
vertently enter a developer solution and affect the development 
characteristics. An analysis which would detect such traces would 
not only be extremely tedious but also unnecessary since the usual 
sensitometric control strip gives that information quite simply and 

Chemical analyses, then, are not satisfactory when used in place 
of photographic tests but are a necessary supplement to them. Their 
role is not to determine the time of development or the temperature 
that is required to give a given contrast but to insure constant and 
reproducible photographic quality. No matter to what extent 


changes in the ingredients of a developer solution may affect the 
photographic results, the following statement must certainly be 
true: If all of the important constituents of a developer solution 
are held constant, the photographic quality of images developed in 
that solution will be constant. Thus, the aim of the processing 
control should be to control the developer solution itself as well as to 
control the degree of development as indicated by sensitometric test 

The analytical methods presented below have been worked out 
at the Kodak Research Laboratories and most of them have been in 
use over two years. In most cases, ease of manipulation and speed 
have been considered as more important factors than a high degree of 
accuracy. In all cases, the methods are capable of giving results to 
an accuracy of 5 per cent or better. A 500-cc. sample of developer 
solution is sufficient for a complete analysis and one operator can 
make a complete analysis in about half an hour. Analysis for any 
one constituent may be made in a much shorter time. The labora- 
tory space required for these tests is small and little equipment is 
necessary. Most of the tests depend on colorimetric measurements 
and may be run very efficiently in an optical instrument called an 
opacimeter. In this instrument a high-aperture lens system pro- 
vides a light-beam of fixed characteristics. In this beam, glass 
vessels containing the products of the color-forming reactions can be 
placed. The change in light-intensity is measured by means of a 
photosensitive cell whose output is measured directly by a microam- 
meter. Test reactions can be run either in Kohle flasks in the 
instrument, or, when it is desirable to use small amounts of reaction 
solutions, in calibrated test tubes. The opacimeter provides a 
sufficiently high level of illumination so that narrow-band color- 
filters can be placed in the light-beam in order to enhance the effect 
on the photocell when a weaky colored reaction mixture is used. 
This instrument is more fully described in an accompanying paper. 

The presence of iodide in a developer solution has been mentioned 
but no test for it is given. Although it is known that small amounts 
of iodide do have a photographic effect, an analysis for the small 
amounts present in an ordinary developer solution is tedious and time- 
consuming. Analyses made at these Laboratories by Ballard and 
Yutzy have shown that the equilibrium amount of iodide in a developer 
which is used for positive film is only about 0.0005 gram per liter (ex- 
pressed as potassium iodide) and for negative film is only 0.0015 to 

312 R. M. EVANS AND W. T. HANSON, JR. [j. s. M. P. E. 

0.0020 gram per liter. In both cases, equilibrium is reached when less 
than 5 feet of film per liter of solution has been developed. In the 
usual case, the equilibrium is rapidly established and the total amount 
of iodide present does not vary appreciably. There is no real necessity 
for analysis. It is recommended, however, that when entirely fresh 
solutions are placed in a machine, an amount of potassium iodide 
approximately equivalent to the above figures should be added to the 
solution and a small amount of fogged film (perhaps one foot per 
gallon) should be run through the solution. 

Elon. The analysis for elon is based on the formation of a yellow 
solution when elon reacts with furyl acrolein. Since elon sulfonate 
which is present as an oxidation product undergoes the same reac- 
tion, the elon must be separated from the developer solution by ex- 
traction. Lehmann and Tausch 3 have published an analytical 
method for elon in which the elon was extracted for several hours in a 
continuous extraction apparatus and then determined by iodo- 
metric titration. This method gives accurate results but is too 
time-consuming to be used as a control method. While the method 
outlined here is not as accurate as the Lehmann and Tausch method, 
it has the merit that it is rapid and it is felt that in many cases rapid- 
ity is more important than extreme accuracy. One objection to the 
present method is that the results are affected by small deviations 
from the exact procedure and the analyst must become thoroughly 
familiar with the details of the method before satisfactory results 
can be obtained. However, satisfactory results can be obtained and 
in the absence of a more easily controlled analysis the present method 
is presented. 


(1) Buffer at pU 8.4 
Trisodium phosphate 150 gm. 
Water 960 cc. 
Cone, hydrochloric acid 40 cc. 

(2) Furyl Acrolein 10 gm. 
Ethyl ether 200 cc. 

(This solution is stable only a few weeks and should not be made up in large 

amounts nor should the solid be stored for long periods of time.) 

Ethyl acetate 

Concentrated hydrochloric acid 

Solid sodium carbonate 


Solid sodium chloride 



One 250-cc. separatory funnel 

One 250-cc. Erlenmeyer flask 

One 125-cc. Erlenmeyer flask 

Two test tubes 

Pipettes 1, 2, 5, and 10 cc. 

One 50-cc. graduated cylinder 

One mechanical shaker 

Two storage bottles 

One No. 47 Wratten filter 

Opacimeter or its equivalent 

Procedure. To 50 cc. of developer solution in a 250-cc. Erlen- 
meyer flask are added a few drops of phenolphthalein and sufficient 
concentrated hydrochloric acid to destroy the pink color. An 
addition of solid sodium carbonate to just restore this color is made 
and then 50 cc. of the stock buffer solution No. 1, 30 gm. of solid 
sodium chloride, and 50 cc. of ethyl acetate are added. This is 
sufficient sodium chloride to form a saturated solution. The mix- 
ture is shaken for five minutes on a mechanical shaker. The pink 
color of the phenolphthalein disappears during this shaking. The 
mixture is poured into a separatory funnel and, after a few minutes, 
the water layer is drawn off. From 2 to 10 cc. of the ethyl acetate 
solution are added to 25 cc. of water and 2 cc. of concentrated hydro- 
chloric acid in a 125-cc. flask to which is also added 10 cc. of the furyl 
acrolein stock solution No. 2. This is shaken for five minutes on the 
mechanical shaker and then allowed to stand for five minutes in a 
separatory funnel. The water layer at the bottom is poured into a 
standard test tube and its transmission is read on the opacimeter 
through a No. 47 Wratten filter. The elon concentration is de- 
termined from an empirical calibration curve made up by analyzing 
known fresh solutions. 

The total amount of elon plus elon sulfonate which is present can 
be determined by allowing 1 to 5 cc. of the original developer solution 
(in place of the ethyl acetate extract) to react with the furyl acrolein. 
A calibration curve must be prepared following this procedure. 

Because of the sensitivity of this test to small changes in the con- 
ditions under which it is carried out, each step in the procedure must 
be carefully controlled. The extraction of elon is a function of both 
pH and total salt content, so both of these factors must be reproduced 
accurately. The pH of the stock buffer solution must not vary more 

314 R. M. EVANS AND W. T. HANSON, JR. [j. s. M. P. E. 

than 0.1 from 8.4 and the amount of sodium chloride added before 
the extraction must be sufficient to saturate the solution. The 
reaction between elon and furyl acrolein precedes slowly and suffi- 
cient time for its completion can not be allowed, so the time of shak- 
ing at this stage of the analysis as well as the time of standing in the 
separatory funnel after shaking must be carefully reproduced. With 
these precautions properly followed and a calibration curve pre- 
pared for a given developer formula, an accuracy of about five per 
cent can be achieved. If the analysis must be made on an unknown 
developer formula, less accurate results can be expected, but, if 
necessary, the first rough analysis can be followed by a calibration 
curve and another analysis. 

Such a procedure takes about two or three hours and should be 
necessary only in rare cases. Under ordinary conditions the test 
takes about 15 minutes. 

Hydroquinone and Hydroquinone Sulfonate. The test for these 
compounds is based on the measurement of the intensity of the color 
formed when they are oxidized by potassium ferricyanide in the pres- 
ence of sodium sulfite. Both hydroquinone and hydroquinone sul- 
fonate give the same color but can be separated by acidifying the 
developer solution and extracting the hydroquinone with ethyl 
acetate. The sulfonate remains in the water layer. From the 
stoichiometry of the titration with ferricyanide it appears that the 
colored product is a semiquinone of hydroquinone disulfonate but 
no definite proof of this has been undertaken. The exact procedure 
is as follows : 


(1) Sodium sulfite 30 gm. 
Sodium carbonate 20 gm. 
Water to 1 liter 

(2) Potassium ferricyanide 0.2 molal (approximately) 
(5) Bromophenol blue (0.1 per cent water solution) 

Concentrated hydrochloric acid 

Ethyl acetate 

All solutions are fairly stable and can be kept for several weeks. None of 

them need be standardized. 


One 250-cc. separatory funnel 
One 50-cc. graduate 


Pipettes 1, 2, and 5 cc. 

One 300-cc. Kohle flask with side arm for air agitation 

One No. 44 Wratten filter 

Two storage bottles 

Compressed air (low pressure) 

Procedure. Hydroquinone. To 50 cc. of developer solution are 
added a few drops of bromphenol blue and then concentrated hydro- 
chloric acid is added until the solution just turns yellow. Fifty cc. 
of ethyl acetate are added and the mixture shaken by hand for one 
minute in a separatory funnel. This is then allowed to stand until 
two layers have separated. One to 5 cc. of the ethyl acetate layer 
(the upper layer) are added to 275 cc. of water and 25 cc. of stock 
solution No. 2 in the Kohle flask. This solution is placed in the 
opacimeter and agitated by air introduced through a glass tube 
inserted in the flask. The No. 44 filter is placed in the beam of light, 
the microammeter set so that the reading is at a maximum, and ferri- 
cyanide solution is poured in slowly and uniformly until the deflec- 
tion of the galvanometer needle is a minimum. This point of mini- 
mum deflection, when read on the calibration curve, gives the amount 
of hydroquinone present. 

If, instead of using 1 to 5 cc. of the ethyl acetate layer in the above 
procedure, an equal amount of the water layer is used, the hydro- 
quinone sulfonate rather than the hydroquinone causes the color, 
and from the proper calibration curve its concentration can be de- 
termined. The total amount of hydroquinone and hydroquinone 
sulfonate can be checked by running the test on the original developer 
solution without extraction. 

In order to achieve the greatest accuracy, calibration curves 
should be obtained for each developer formula because, although the 
test is specified for hydroquinone in an ordinary MQ developer, 
different total salt concentrations affect the extraction and, con- 
sequently, the determination of free hydroquinone. Under the, 
proper conditions, the test gives analyses with an error of much less 
than 5 per cent. 

Sodium Sulfite. The test for sulfite is based on the fact that 
certain dyes are quantitatively bleached by sulfite solutions. 


(1) Isopropyl alcohol 100 cc. 
Water 900 cc. 

316 R. M. EVANS AND W. T. HANSON, JR. [J. S. M. P. E. 

Glacial acetic acid 1 cc. 

Acid green L (No. 764) 1 gm. 

Filter through No. 42 filter paper 

pH = 3.9 
(2) Sodium carbonate 30 gm. 

Sodium bicarbonate 30 cc. 

Water to make 1 liter 

pH = 9.4 
Both solutions are stable for several months. 


Two storage bottles 

One small filter funnel and paper 

Pipettes, 1 and 10 cc. 

Two test tubes 

One No. 23 Wratten filter 

Procedure. To 1 cc. of the developer solution are added 10 cc. of 
stock solution No. 2 and 10 cc. of stock solution No. 1. This order 
of addition of these solutions must be followed because the bleaching 
of the dye is affected by />H and must be carried out in a well buffered 
solution. Since the dye is not stable for long periods of time if 
dissolved in the buffer itself, it must be kept in the acid solution as 
recommended. The transmission of this partially bleached dye 
solution is measured on the opacimeter through a Wratten No. 22 
or 25 filter and the sulfite concentration is determined from a cali- 
bration curve. 

Bromide. Bromide is determined by titrating with a standardized 
silver nitrate solution, using metanil yellow as an adsorption in- 
dicator.* Chloride or any other material which forms a salt less 
soluble than silver chloride will be included by this test and in the 
presence of unknown amounts of such materials the method can not 
be used. A method which eliminates these objections has been 
worked out by Ballard of these Laboratories and has been used 
quite successfully, but since it is more time-consuming than the 
present method, it will not be included here. Iodide may be con- 
sidered constant, as was pointed out above. 

*This method was worked out at the Kodak West Coast Laboratories (Holly- 
wood, Calif.) by Atkinson. Shaner, and Huse. 



(1) Silver nitrate (standardized) about 0.03 N 

(2) Metanil yellow (0.1 per cent water solution) 
Concentrated sulfuric acid 


One 50-cc. burette and holder 

One 15-cc. pipette 

One 250-cc. Erlenmeyer flask 

Procedure. To 15 cc. of developer solution are added 5 to 10 cc. 
of concentrated sulfuric acid. This is then diluted to about 100 cc. 
and cooled. Two or three drops of metanil yellow are added and 
then titrated with standard silver nitrate solution until the solu- 
tion changes from purple to red. The usual volumetric calculations 
can be used to determine the amount of halide present or a calibra- 
tion curve can be prepared. The change of color at the end point is 
sometimes rather difficult to distinguish but with a little experience 
under the proper lighting conditions the titration can be controlled 
to an accuracy of two or three per cent. 

Carbonate. The analysis for carbonate is based on the measure- 
ment of the pressure developed in a nearly constant volume system 
held at constant temperature, when carbon dioxide is released from 
the developer by the addition of a strong acid. In order to avoid 
the formation of sulfur dioxide from the sulfite in the solution, 
quinone must be added. This reacts with the sulfite to form hydro - 
quinone monosulfonate. 


Concentrated hydrochloric acid 
Solid quinone 


One 500-cc. Erlenmeyer flask (calibrated) 
One stopper bucket (as shown in Fig. 2) 
One open-end manometer (filled with CCL.) 
One burette 
Pipettes, 5 and 10 cc. 
Constant-temperature water bath 
Rubber tubing 


R. M. EVANS AND W. T. HANSON, JR. [j. s. M. P. E. 

Procedure. Five cc. of developer solution and 10 cc. of water are 
pipetted into the calibrated Erlenmeyer flask and about 0.5 gram of 
solid quinone is added. Shake thoroughly. Two cc. of concen- 
trated hydrochloric acid are run into the stopper bucket from a 
burette and the stopper is inserted in the flask. This is then im- 
mersed in a constant temperature bath and allowed to come to 

temperature equilibrium. The 
manometer is then connected to 
the arm of the stopper bucket and 
the flask is tilted so that the acid 
is poured into the developer solu- 
tion. After it has been shaken thor- 
oughly, the flask is again brought 
to temperature equilibrium and the 
pressure read from the manometer. 
The carbonate concentration is de- 
termined from a calibration curve. 

The exact size of the flask used in 
the analysis and the temperature at 
which it is carried out are imma- 
terial as long as the calibration 
curve is prepared under the same 
conditions. For this reason, it 
might be desirable to prepare cali- 
bration curves at several tempera- 
tures and then to use an ordinary 
sink with hot and cold water mixed 
to give a fairly constant tempera- 
ture, as the constant temperature 
bath. Under such conditions, where 
the temperature might vary 0.1 
the test is accurate to better than 10 per cent. In most cases this 
accuracy is quite sufficient, especially if the pH of the solution is 
determined. However, an accuracy of 3 to 4 per cent can be 
obtained by carefully controlling the condition of the test. 

Sulfate. The sulfate analysis is based on the precipitation of 
barium sulfate by the addition of barium chloride after removal of 
the sulfite and carbonate from the developer solution. The amount 
of barium sulfate formed is determined turbidimetrically by means of 
the opacimeter. 

FIG. 2. Stopper bucket and 
flask for use in carbonate analy- 



(1) Barium chloride dihydrate 10 gm. 
Water 1 liter 

Concentrated hydrochloric acid 


One 50-cc. graduate 

One 50-cc. burette 

Two test tubes 

Pipettes 2, 10, and 25 cc. 

One 125-cc. Erlenmeyer flask 

Low-pressure steam (if available) or hot plate 

One filter funnel and filter paper 

Procedure. To 25 cc. of developer solution in an Erlenmeyer flask 
10 cc. of concentrated hydrochloric acid are added and the solution 
is boiled or bubbled with steam for two or three minutes in order to 
remove sulfur dioxide and carbon dioxide. This is cooled and 
diluted to 100 cc. in the graduated cylinder and, if the solution is 
turbid at this point, it must be filtered. Two cc. of this solution are 
pipetted into 25 cc. of stock solution No. 1 in a standard test tube, 
a cork stopper is inserted, and the tube is inverted, three or four times. 
Its transmission is then read on the opacimeter and the sulfate con- 
centration determined from a calibration curve. 

pR. The pR of developer solutions can sometimes be measured 
colorimetrically by means of indicators but, in many cases, the solu- 
tions are colored to such an extent that colorimetric observations are 
impracticable and electrometric methods must therefore be used. 
The usual types of glass electrodes used in conjunction with a stand- 
ard reference electrode and an ordinary potentiometer are quite 
satisfactory. At the present time, most glass electrodes have a 
fairly large sodium-ion error at high pR values but there is now enough 
information in the chemical literature so that corrections for such 
errors can be made with sufficient accuracy. In any case where 
variations of pR rather than absolute values are desired, the errors 
may be neglected. The most important use of pR in developer 
analysis is to obtain a quick check in cases where large errors of 
mixing are suspected or where it is desired to distinguish between too 
greatly different formulas such as those used for a negative and a 
positive film. 



1 EVANS, R. M.: "Maintenance of a Developer by Continuous Replenish- 
ment," /. Soc. Mot. Pict. Eng., XXXI (Sept., 1938), p. 273. 

2 EVANS, R. M., AND HANSON, W. T., JR. : "Reduction Potential and the Com- 
position of an MQ Developer," /. Soc. Mot. Pict. Eng., XXX (May, 1938), p. 

3 LEHMANN, E., AND TAUSCH, E.: "Zum Chemismus der Metol-Hydrochinon 
Entwicklung," Phot. Korr., 71 (Feb., 1935), p. 17; 71 (March, 1935), p. 35. 


MR. DEPUE: What is the best length of time for processing positive film in 
the machine, two minutes or three and a half? 

MR. EVANS: That depends a good deal upon the machine and the precision 
with which you wish to repeat results. At two minutes, of course, it is much more 
difficult to repeat results than at five or six. I do not think it can be stated 
whether one is to be preferred to the other. 

MR. SCHMIDT: I understand that upon the addition of alkali to the developer 
a certain time is required for the pH to reach the definite value that corresponds to 
the equilibrium. 

MR. EVANS: Yes. In some cases half a day is required before the pH equi- 
librium is established so it can be read. 

MR. SCHMIDT: Do you propose an explanation of that? I expected that the 
reaction between the ions would take place in a shorter time. 

MR. EVANS: We expected that also, but it does not appear to be. Perhaps it 
has to do with the organic constituents that are present. 

MR. CRABTREE: Do you estimate the sulfonates formed in the developer? 

MR. EVANS: The sulfonates are included in the analysis. They are not 
strictly necessary unless it is desired to know what the original formula was. The 
sum of acting developing agents and their sulfonates is equal to the concentration 
in the replenisher of the original compound, and accordingly it is sometimes inter- 
esting to know whether a change in the bath is due to the concentration in the 


Summary. The opacimeter is an optical instrument designed to measure the light- 
transmission of a colored or turbid solution. A Loewenthal photronic type light- 
sensitive cell connected to a microammeter is used to measure the intensity of the light 
transmitted by the solution under test. The light-intensity falling on the sensitive cell 
is kept within a fixed range by varying the distance of the cell from the source. The 
instrument is arranged so that a 30-cc. test tube or a 300-cc. Kohle flask may contain 
the reaction mixture. The results of analyses are determined from calibration curves 
prepared from known solutions. 

A great many quantitative tests for the chemical constituents of 
solutions lend themselves readily to measurements based on the 
change in light-transmission of the solution after addition of suitable 
reagents. A wide variety of optical instruments designed to make 
measurements of this sort have been in use for a long time. The 
purpose of this article is to describe a new design of such an instru- 
ment which possesses several advantages. 

The name "opacimeter" seems a suitable one to give to the instru- 
ment shown in Fig. 1. A Loewenthal photronic type light-sensitive 
cell (chosen because of its stability and high sensitivity) is used to 
measure the intensity of the light transmitted by the solutions under 
test. This cell is color-selective, and its sensitivity depends upon the 
intensity level of the incident light. For these reasons, the optical, 
system shown diagrammatically is designed to work at a constant 
color-temperature of the light-source. The light-intensity falling 
on the Loewenthal cell is kept within a fixed range by varying the 
distance of the cell from an opal glass diffusing disk illuminated by 
the light passing through the solution under test. In order to cut out 
the infrared sensitivity of the light-receiver and also to prevent heat- 
rays from reaching the test solutions, a flask containing a 4-per cent 
copper sulfate solution is placed on the light-source side of the flask 

* Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 28, 
1938. Communication No. 697 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 




used in making the tests. A high-aperture lens system maintains a 
parallel beam of light passing through the solution in the test flask, 
thus permitting a more efficient system. As long as the liquid level 
is a small distance above the top of the light-path, changes in this 
level have no effect on the amount of light reaching the light-receiver. 

FIG. 1. Diagram of optical system. 

FIG. 2. Diagram showing scheme for air agitation within Kohle flask. 
FIG. 3. Test-tube holder. 

The opacimeter is designed to use Kohle culture flasks as test cells, 
these being readily available, easily cleaned, and quite uniform in 
dimensions. The procedure followed is to make the calibration run 
on any given test in the same flask as that to be used in testing the 
solution. In case of breakage, a new flask may be calibrated easily. 
In Fig. 2 is shown an air-stirring system built into one of the Kohle 


flasks. This consists of a bent glass tube ending in a fine orifice. 
The large end of the tube is attached to a source of compressed air, 
the fine air-jet producing very efficient circulation in the solution in 
the flask, air bubbles passing around the outside of the flask and not 
entering that portion of the solution lying in the light-path. As can 
be seen from the photograph (Fig. 4) the test flasks do not need to be 
removed from the instrument in order to introduce test liquids ; thus, 
continuously stirred titrations can be run by using a burette held in 
place above the opening of the air-stirring flask just mentioned. 
When it is desirable to use a small amount of solution in making a 
test, the Kohle flask can be replaced by a test-tube holder, such as 

FIG. 4. Photograph of instrument, with light guards removed. 

shown in Fig. 3. The test tube when filled with solution forms a 
cylindrical lens which, in conjunction with the main optics, covers the 
opal-glass diffusing disk with light. Ordinary test tubes can be used 
for this purpose, provided each one is calibrated for the particular test 
with which it is to be used. 

In most cases, tests are run by adjusting the position of the light- 
receiver so that the microammeter in series with it gives a deflection' 
of 200/z with a blank solution in the test flask and with a suitable 
Wratten light-filter in the holder shown in Fig. 1. The decrease in 
transmission of the solution after the test reaction has taken place is 
read on the meter scale in microamperes. This reading can then be 
converted into the amount of the particular ingredient by the use of a 
calibration curve. If it is desired to measure the optical density of 


the solution, meter readings can be converted to densities from the 
relation : 

Density = log 


A 200-watt, 110- volt projection lamp (with a prefocus base to 
minimize adjustment when replacing a burned out lamp) gives suffi- 
cient light for most tests, even when such a low-transmission light 
filter as Wratten No. 53 is used. The meter used in conjunction with 
the Loewenthal cell is a Weston model No. 301 DC microammeter, 
reading n at full scale. 

The use of the instrument is not restricted to chemical reactions 
giving rise to a clear, colored solution. In practice, it has been found 
that the amount of constituent present can be reliably determined by 
measuring the change in light- transmission arising from the formation 
of uniformly dispersed precipitates, especially if settling of the pre- 
cipitates is prevented by use of suitable dispersing agents. 

In making measurements on nonscattering colored solutions, the 
use of colored filters in the light-beam greatly increases the sensitivity 
of the particular test being made. Common procedure in these cases 
is to choose a filter having a strong absorption band in the spectral 
region where the transmission of the colored solution being measured 
is a maximum. In the case of reactions giving several transmission 
bands owing to the presence in solution of constituents other than the 
one under test, the use of a proper color-filter makes it possible to 
separate the useful transmission band from the others. 


During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 


During the past few years the Research and Engineering Departments of this 
company have been searching for a device or devices that would permit changes 
in the design of projection equipment that would result in greatly improved film 
presentation. Many ideas were considered and rejected, some because of extreme 
complications, and all because nothing was found that would compare favorably 
so far as screen results were concerned, with equipment of our earlier designs. 
After making this decision approximately two years ago, it was decided to im- 
prove, so far as we possibly could, upon what were our earlier conceptions of the 
best available mechanisms, with the result that about two months ago there was 
released to the industry the company's latest development in motion picture 
projectors, the Simplex E-7 mechanism (Fig. 1). 

In considering the design of modern motion picture projection equipment it is 
necessary to deal with two major requirements: (1) greater screen illumination, 
without increasing the light coming from the arc or other illuminating means, 
and (2) increased steadiness of the projected picture. The means whereby these 
have been accomplished, together with a brief summary of other changes and im- 
provements, constitute the subject of this paper. 

Tn the conventional motion picture projector mechanism there are a revolving 
shutter either in the front or in the rear which cuts off the light as the film is 
pulled down past the aperture plate by the intermittent movement, and openings 
in the shutter, either front or rear, which allow the light-beam to pass through the 
film to the screen while the film is at rest in front of the aperture plate. Increased 
illumination obtained from the E-7 projector has been brought about by placing a 
second shutter in front of the lens (Fig. 2), this shutter being attached to the same 
shutter shaft and revolving in the same direction as the rear shutter or the shutter 
between the illuminant and the aperture plate. By this design it is possible to 
cut off half of the light-beam behind the aperture plate, and half of the picture at 

* Presented at the 1938 Spring Meeting at Washington, D. C. ; received April 
14, 1938. 

** International Projector Corp., New York, N. Y. 




the same instant in front of the lens, since the image is inverted after passing 
through the lens. We are thus able (since it is not then necessary, as in the case 
of one shutter, to cut the entire picture from the screen before moving the next 
one into position) to cut the top and bottom halves of the picture at the same 
instant and eliminate approximately 20 degrees from each shutter blade, and 
hence pass that much more light to the screen. This results in an approximate in- 
crease of from 12 to 15 per cent in screen illumination. 

FIG. 1. Simplex E-7 projector. 

This result is obviously attained without increasing the speed of any part of 
the mechanism since, as before stated, both shutters revolve at the same speed 
(1440 rpm.), being attached to the same shutter shaft. Both shutters are housed 
in suitable protective guards, and means are provided for the easy removal of 
these guards when necessary for cleaning purposes. Attached to the rear shutter, 
between the source of illumination and the aperture plate, are specially designed 
vanes, the function of which is to create a partial vacuum in and around the 
aperture plate and remove therefrom at high velocity the heat created by the 
illuminated spot and keep the entire rear of the projector cool enough to touch 
with the fingers even when using high-intensity arcs. 

To set the shutters in exact synchronism and in proper relation to the 
intermittent movement, a shutter-setting device is supplied with each pair of 
mechanisms. With this device the shutters may be set in an extremely simple 

Mar., 1939] 



manner and with a greater degree of accuracy than was possible with earlier 

A steadier picture is obtained both vertically and laterally, first, through new 
developments in intermittent movement design, which allow far greater accuracy 
in manufacture, plus a hardened and ground intermittent sprocket on which the 
64 radii of the teeth are ground to extreme accuracy; and, second, by the addi- 
tion of edge-guiding in the film-trap, which maintains the film in a constant lateral 
position and does not allow the film to weave slightly as in former designs. 

To eliminate the possibility of improper or inadequate lubrication, the equip- 
ment is provided with the Bijur one-shot oiling system (Fig. 3). This system has 
proved its merit in the finest types of accounting machines, sewing machines, 
electric lamp machinery, etc.; it is incorporated in the best American trucks and 
ambulances, and in the highest grade foreign automobiles. 

FIG. 2. Synchronized front and rear shutters. 

As applied to the new projector, this system consists of a piston pump which 
delivers at each impulse a metered quantity of filtered oil to a distribution system 
where, by means of meter units, this measured quantity is proportioned to each 
bearing in predetermined quantities. Check- valves in the meter units prevent 
draining the oil lines between "shots." The system is provided with a double set 
of dense felt filters, the one in the pump being the denser and serving to filter the 
reservoir oil; the other set of filters is in the individual meter units and is for 
protection of the units against chips and dirt before and during assembly. This 
combination of filtering assures a clean supply of oil at every bearing. The 
Bijur Company advise that they have as yet found no indication of a limit to the 
life of the filters when used with a straight mineral oil. The pump develops a 
pressure of 35 pounds per square inch. 

The small tubes leading from the meter units to the bearings are so propor- 
tioned, as to ratio of wall thickness to bore, that they will not collapse even when 
bent double in a vise, so there is no way in which they could be stopped up with- 
out a type of handling that would also damage the mechanism as a whole. With 




.J3 f> 

'"S 5 


a lubricating system such as this the only place in which it is necessary to see the 
oil is in the pump unit, and a sight-glass is provided for this purpose. 

Such bearings as are not reached by this lubricating system are the ball bearings 
that carry the shutter-shaft assembly and the lower bearing of the oblique shaft. 
These are of the sealed, grease-packed, dustproof type, and do not need attention 
for a number of years. Oil-can lubrication is required only to fill the oil reservoir 
of the Bijur system and the intermittent movement, which will be discussed later. 

Considering fire protection of paramount importance, the equipment is sup- 
plied with a positive-acting fire-shutter between the rear shutter and the film 
aperture (Fig. 4), which is operated through a centrifugally operated disk mounted 
on the revolving shutter- shaft. When the projector is at rest this disk lies at an 

FIG. 5. Automatic fire-shutter safety trip. 

angle with relation to the shutter-shaft and when the projector is in operation, 
centrifugal motion straightens up, so to speak, and through a unique linkage 
device raises the fire-shutter out of the beam of light. 

It is well known that on a properly designed projector mechanism, and one that 
is kept in good repair, it is not possible under normal circumstances to burn more 
than one frame of film at the aperture plate should a splice part at the intermittent 
sprocket, and this, incidentally, is the only time it is possible during normal op- 
eration of a projector for any kind of fire to occur. However, to eliminate even 
this cause of fire, the apparatus is provided with an automatic fire-shutter safety 
trip (Fig. 5), which operates in connection with the automatic fire-shutter and 
instantaneously drops the latter should a splice part at the intermittent sprocket. 
The unit is operated by the slightest increase in size of the upper loop, and the 



action is instantaneous, the fire-shutter dropping before the film has a chance to 
ignite. This means increased protection to the projectionist and theater owner. 
The device is simply attached and may readily be removed and replaced. 

A newly designed film-gate has been provided, of much heavier construction 
than any of its predecessors and readily removable by simply removing two thumb- 
nuts and sliding it from its two supporting studs (Fig. 6). This gate is now formed 
from one heavy steel stamping which supports along its entire length pressure 
pads of new design, the tension on all of which, through self-equalizing cone 


%i f 

FIG. 6. Film gate: (left) rear view; (right) front view. 

springs, is readily adjusted by the projectionist while the projector is in operation. 
The base of the gate supports the intermittent sprocket tension shoe which also 
is provided with an adjustable tension unit. With this type of gate, and due to 
the proper placement of tension shoes, it has been found possible to lessen the 
tension considerably and at the same time maintain a much steadier picture than 

The gate is mounted on an opening and closing unit of entirely new design and 
is locked solidly in both its open and closed position. Provision is made for 
removing entirely any lateral displacement of the gate due to wear, and this 
combination definitely prevents any "jiggling" of the gate such as was some- 
times evident in earlier models. The entire gate is provided with a very simple 




lateral adjustment by means of which it may be correctly aligned with the runners 
on the film-trap. 

The film-trap is of completely new and original design and may now be removed 
entirely for cleaning purposes as may the gate (Fig. 7). This is accomplished 
simply by the removal of two screws, whereupon the film-trap may be slid off 
toward the projectionist. The film-trap is provided with the conventional 
lateral guide-rollers, but, in addition thereto, edge-guiding channels have been 
added which, in cooperation with the lateral guide-rollers, maintain the edge of 
the film steadily against the edge of the guide, thus eliminating all sidesway during 
film travel. The film-handling parts of both the gate and film-trap are readily 
removable for replacement when wear becomes apparent, and it is no longer 
necessary to tear down the entire projector when such is the case. 

FIG. 8. Framing lamp and spot sight box. 

As in the case of previous film-trap and gate design in Simplex projectors, the 
emulsion side is always toward the film-trap runners; thus, variations in film 
thickness, as between standard production film and newsreel stock, will not affect 
the definition of the projected picture; thus, it is not necessary to re-focus the 
lens to compensate for the difference in the position of the emulsion as is the case 
with the old Powers projector mechanism and other equipment of similar design. 

An ingenious framing lamp and spot sight box assembly is mounted between 
the rear shutter and the film-trap (Fig. 8). A small incandescent lamp of the 
bayonet type is pivotally mounted in this assembly and operable only when the 
fire-shutter is raised manually during the process of threading the film into the 
projector; thus, a strong, direct beam of light is projected through the aperture 
plate by means of which the projectionist may accurately select the frame of film 
to be placed over the latter. The lamp is lighted through a small mercoid switch 
and extinguished upon release of the fire-shutter lever which automatically takes 
the framing lamp assembly out of the path of the projection lamp beam and ex- 
tinguishes it at the same time. 

Mar., 1939 J 



The spot sight box in which this assembly is mounted is provided with a number 
of air-cooled fins for rapid dissipation of heat from the projection lamp-beam. A 
highly polished nickel-plated copper baffle, together with two additional copper 
baffles, form part of the heat-reflecting unit in this assembly, and this helps 
further to cool the rear of the mechanism. The entire assembly is readily remov- 
able for cleaning, and engages the electrical circuit by means of pin plugs when in 
its proper operating position. 

The intermittent movement in this equipment is of the conventional double- 
bearing type, similar to that provided in earlier Simplex mechanisms (Fig. 9). 
It has been greatly improved, however, as to oil sealing, and is provided with 

FIG. 9. Cut-away views of intermittent movement. 

means whereby it is impossible to insert a greater quantity of oil than is required 
for proper operation. This eliminates the possibility of the projectionist's over- 
filling the oil-well and thus allowing the lubricant to spill over; and at the same 
time makes it possible at all times for him to see through the sight glasses in the 
movement, that the oil level is correctly maintained. 

The entire movement is of considerably heavier construction throughout, and 
its design, as before stated, allows for far more accurate construction than was 
possible in any previous movement. In addition to being leakproof it is practi- 
cally bindproof, since properly designed spiral grooves in connection with oil 
channels are provided in the revolving shafts and bearings which carry oil to all 
parts needing constant lubrication. In addition to this, perfect lubrication be- 
tween the cam ring and the star radius is assured, since oil is forced through two 
channels in the cam forming a cushion of oil between the star radius and the cam 



ring when they lock together while the picture is being projected. This also 
cushions the blow between the two units and makes for a quiet-running unit. 
The movement may be lubricated from either the non-operating or operating side. 

One of the important features in connection with this intermittent movement 
is the fact that it may be readily removed for cleaning, or parts replaced with- 
out disturbing any of the major parts of the projector mechanism or sound- 
reproducing unit and this from the operating side of the mechanism. 

Positive synchronism, without backlash or lost motion, is assured between the 
intermittent movement and the revolving shutters when framing by the uniquely 
designed assembly now performing this function. The shutter-shaft passes 
through an assembly similar to a cylinder and piston in automobile design (Fig. 
10), and fastened to the piston through a ball-race is the shutter driving gear by 
means of which the shutter-shaft is driven through a woodruff key. Attached 


m J 

FIG. 10. New ring type governor. 

also to the piston is a pivoted arm, the lower end of which fetches up solidly 
against a plunger pin operated by the framing cam of the intermittent movement 

The entire assembly is held under substantial tension by means of a heavy 
coiled spring, one end of which is held under tension by a collar on the shutter- 
shaft and revolving with it, and the other end of which fetches up solidly against 
the ball-race attached to the gear. This spring performs two functions : it forces 
the piston rearward at all times, and at the same time removes any slight end- 
play in the shutter shaft and framing device synchronizing assembly. 

In operation, when the framing handle is turned in one direction, the intermit- 
tent movement, complete with its framing cam, revolves in its housing, forces the 
plunger against the pivoted arm, which in turn moves the piston and gear as- 
sembly forward against the spring compression, thus revolving the spiral gear and 
shutter-shaft the exact amount necessary to maintain synchronism between the 
intermittent movement and the revolving shutters. When the framing handle is 
turned in the opposite direction, the entire assembly performs exactly the same 
function, except that the compression spring forces the piston and gear assembly 


rearward, and thus the same synchronism is obtained with any position of the 
framing handle and intermittent sprocket. 

All bevel gears have been eliminated and, as a matter of fact, the number of 
gears has been greatly reduced. Spiral gears alone now form the driving equip- 
ment, and thus the noise-level during operation has been tremendously reduced. 
The face of the main drive gears has been increased in cross-section as a protection 
against the high starting torque of the modern sound-head, and these gears now 
operate on hardened and ground studs rigidly attached to the center frame. The 
area of the bearings of the gears that revolve upon these studs has also been 
greatly increased, and lubrication is provided through the Bijur one-shot oiling 
system to the center of the studs, forcing in clean oil all the time and washing any 
dirty lubricant out on the non-operating side of the projector only; thus re- 
bushing of the main frame in this connection has been eliminated, and much 
longer life is assured and cost of maintenance reduced. 

Wherever the finest accuracy is not required non-scoring bearing material is 
used ; but where extreme accuracy is required, and this material can not be relied 
upon satisfactorily, the type of bearings best suited for their proper function, such 
as ball bearings on the shutter shaft, and burnished cast-iron bearings for hard- 
ened and ground shafts, are used. 

Lens focusing is accomplished from either inside or outside the mechanism, 
making it possible at all times to control readily the definition of the projected 

The mechanism is designed to fit any existing standard sound-reproducing 
apparatus. The interior is finished in pearl-gray enamel, to facilitate ob- 
servation of the film travel. This light interior also lends itself to cleanliness, and 
is brightly illuminated by the additional threading lamp provided in the upper 
right-hand corner of the operating side of the mechanism. This latter lamp 
eliminates the need for the old-fashioned trouble-lamp heretofore necessary for 
checking during threading operations. 




Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice-P resident 

W. C. KUNZMANN. Convention Vice-President 

J. I. CRABTREE, Editorial Vice-President 

L. L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 

J. HABER, Chairman, Publicity Committee 

Pacific Coast Papers Committee 

L. A. AICHOLTZ, Chairman 




Reception and Local Arrangements 

H. G. TASKER, Chairman 







Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation 

G. A. CHAMBERS, Chairman 






Convention Projection 

H. GRIFFIN, Chairman 






Officers and Members of Los Angeles Projectionists Local No. 150 

Banquet and Dance 

N. LEVINSON, Chairman 






Ladies' Reception Committee 

MRS. N. LEVINSON, Hostess 

assisted by 







J. HABER, Chairman 



New Equipment Exhibit 
J. G. FRAYNE, Chairman 



O. F. NEU 


Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Special hotel rates, guaranteed to SMPE delegates, European plan, will be as 
follows : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8 . 00 

Parlor suite and bath, 2 persons 12.00 

338 1939 SPRING CONVENTION [j. s. M. p. E. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available 
to those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately 
upon arriving at the Hotel. Convention badges and identification cards will 
be supplied which will be required for admittance to the various sessions, the 
studios, and several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges : 


Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 147.50 23.65 

Detroit 106.75 19.20 

New York 139.75 22.85 

Rochester 124.05 20.50 

Cleveland 110.00 19.20 

Philadelphia 135.50 22.35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips, sixty-day limits. Arrange- 
ments may be made with the railroads to take different routes going and coming, 
if so desired, but once the choice is made it must be adhered to, as changes in the 
itinerary may be effected only with considerable difficulty and formality. Dele- 
gates should consult their local passenger agents as to schedules, rates, and stop- 
over privileges. 

San Francisco Fair 

On February 18, 1939, the Golden Gate Exposition opened at San Francisco, 
an overnight trip from Hollywood. The exposition will last throughout the sum- 
mer so that opportunity will be afforded the eastern members of the Society to 
take in this attraction on their Convention trip. Special arrangements have been 
made with the Hotel Empire at San Francisco for Convention delegates visiting 
the Fair, at the following daily rates : 

One person, room and bath $3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 


Parlor and bedroom for two persons 8 . 00 and up 

Two large bedrooms, each with private bath and a living 

room; for four persons 16.00 

Reservations can be made either by writing directly to the Hotel Empire or by 
addressing Mr. W. C. Kunzmann, Convention Vice-President, Box 6087, Cleve- 
land, Ohio. 

Mar., 1939] 1939 SPRING CONVENTION 339 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems, and 
arrangements will be made to visit several of the studios. The Local Papers 
Committee under the chairmanship of Mr. L. A. Aicholtz is collaborating closely 
with the General Papers Committee in arranging the details of the program. 
Complete details of the program will be published in a later issue of the JOURNAL. 

Studio Visits 

On the afternoon of Tuesday, April 18th, Paramount Pictures, Inc., will act as 
hosts of the Convention at their Hollywood Studio. The program will be in 
charge of Messrs. L. L. Ryder and H. G. Tasker. On the afternoon of Thursday, 
April 20th, the delegates of the Convention will be entertained at the studio of 
Warner Brothers First National, Inc., at Burbank. The program of the afternoon 
will be under the supervision of Mr. N. Levinson. 

Semi- Annual Banquet and Dance 

The Semi- Annual Banquet of the Society will be held at the Hotel on Thursday, 
April 20th. Addresses will be delivered by prominent members of the industry, 
followed by dancing and entertainment. Tables reserved for 8, 10, or 12 persons; 
tickets obtainable at the registration desk. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the general office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. N. Levinson, hostess, and the Ladies' Committee. A 
suite will be provided in the Hotel, where the ladies will register and meet for 
the various events upon their program. Further details will be published in a 
succeeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 
Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 


Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Li- 
brary and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at 
Ocean Park and Venice, Calif.; famous old Spanish missions; Los Angeles Mu- 
seum (housing the SMPE motion picture exhibit); Mexican village and street, 
Los Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, 
and Palm Springs, and special tours may be made throughout the Hollywood 
area, visiting the motion picture and radio studios. 


The following are available from the General Office of the Society, at the prices 
noted. Orders should be accompanied by remittances. 

Aims and Accomplishments. An index of the Transactions from October, 
1916, to December, 1929, containing summaries of all articles, and author and 
classified indexes. One dollar each. 

Journal Index. An index of the JOURNAL from January, 1930, to December, 
1935, containing author and classified indexes. One dollar each. 

SMPE Standards. The revised edition of the SMPE Standards and Recom- 
mended Practice was published in the March, 1938, issue of the JOURNAL, copies 
of which may be obtained for one dollar each. 

Membership Certificates. Engrossed, for framing, containing member's name, 
grade of membership, and date of admission. One dollar each. 

Lapel Buttons. The insignia of the Society, gold filled, with safety screw back. 
One dollar each. 

Journal Binders. Black fabrikoid binders, lettered in gold, holding a year's 
issue of the JOURNAL. Two dollars each. Member's name and the volume 
number lettered in gold upon the backbone at an additional charge of fifty cents 

Test- Films. See advertisement in this issue of the JOURNAL. 



As outlined in the preceding section of this issue, and also as announced on the 
inside front cover, the next Convention of the Society will be held on April 17th- 
21st, inclusive, at Hollywood, Calif., with headquarters at the Hollywood 
Roosevelt Hotel. Full details concerning the program will be published in the 
next issue of the JOURNAL. 


At a meeting held at the Hotel McAlpin, New York, N. Y., on Wednesday, 
February 15th, Mr. Clinton P. Veber, Research Associate of the Department of 
Biophotography at Rutgers University, presented a paper describing "The 
Time Telescope." 

A demonstration of the instrument accompanied the paper, which discussed 
the use and history of time-lapse photography, and also the control, design, and 
operation of the new equipment used at Rutgers University. Films were shown 
illustrating the use of machines in producing spectacular pictures showing the 
life histories of plants and other botanical subjects. 


The first meeting of the year was held on January 24th in the meeting rooms 
of the Western Society of Engineers at Chicago. Mr. E. F. Lowry, Research 
Director of the Continental Electric Company, Chicago, gave an interesting 
talk on "The Theory and Operation of Rectifier Tubes and Cathodes." Briefly 
tracing the history of vacuum-tubes from the beginning to the present day, the 
paper turned to the subject of rectifier tubes, in particular, those of the mercury- 
vapor type. 

Following the talk, Mr. J. G. Black gave a demonstration of a 6-phase mercury- 
vapor rectifier. 


At the Detroit Convention of the Society, on October 31, 1938, the following 
amendment of the Constitution was proposed: 

Article IV, Officers 

It is proposed that the term of office of the Executive Vice-P resident be extended to 
two years, in view of the fact that the terms of all the other vice-presidents are two years. 
Original wording: 

The officers of the Society shall be a President, a Past-President, an Executive 
Vice-President, an Engineering Vice-President, an Editorial Vice- President, a 
Financial Vice-President, a Convention Vice-President, a Secretary, and a Trea- 



The term of office of the President and Past- President shall be two years; of 
the Engineering, Editorial, Financial, and Convention Vice-Presidents, two years; 
and of the Executive Vice-President, Secretary, and Treasurer, one year. Of the 
Engineering, Editorial, Financial, and Convention Vice-Presidents, two shall be 
elected alternately each year or until their successors are chosen. The Presi- 
dent shall not be immediately eligible to succeed himself in office. 
Proposed wording: 

The officers of the Society shall be a President, a Past-President, an Executive 
Vice-President, an Engineering Vice-President, an Editorial Vice-President, a 
Financial Vice-President, a Convention Vice-President, a Secretary, and a 

The term of office of the President, the Past-President, the Executive Vice- 
President, the Engineering Vice-President, the Editorial Vice-President, the 
Financial Vice-President, and the Convention Vice-President shall be two years, 
and the Secretary and the Treasurer one year. Of the Engineering, Editorial, 
Financial, and Convention Vice-Presidents, two shall be elected alternately each 
year, or until their successors are chosen. The President shall not be imme- 
diately eligible to succeed himself in office. 

Adhering to the procedure for voting upon amendments of the Constitution, 
voting ballots were mailed to the voting membership shortly after the Conven- 
tion, and a recent count of the ballots by the Secretary indicated practically 
unanimous approval of this amendment. 


At a recent meeting of the Admissions Committee at the General Office of the 
Society, the following applicants for membership were admitted to the Associate 


270 North Michigan, 1821 Roselyn St., 

Chicago, 111. Philadelphia, Penna. 


6 Pall Mall, 13553 Artesian Ave., 

London, England. Detroit, Mich. 


14 Ballygunge Circular Rd., 119-40 Union Turnpike, 

Calcutta, India. Kew Gardens, N. Y. 


2780 Dewey Ave., 1015 N. Edinburgh, 

Rochester, N. Y. Los Angeles, Calif. 


609 Stratford PL, 1050 Anderson Ave., 

Chicago, 111. Bronx, N. Y. 


12708 Littlefield St., Corti 12, 

Detroit, Mich. Milan, Italy. 


448 Lincoln Ave., 35 E. Wacker Dr., 

Orange, N. J. Chicago, 111. 

Mar., 1939] 




119 LeRoy St., 

New York, N. Y. 
HALL, H. W. 

Beeville, Tex. 
22 Tulpweg, 

Wassenaar, Holland. 
245 W. 55th St., 

New York, N. Y. 
231 S. Witmer St., 

Los Angeles, Calif. 

14668 Abington Rd., 
Detroit, Mich. 


Kincardine, Ontario, Canada. 

1513 Field St., 
Detroit, Mich. 


1223 S. Wabash Ave., 

Chicago, 111. 
931 Ogden Ave., S. E., 
Grand Rapids, Mich. 
Breslin Bldg., 

Louisville, Ky. 

614 Frelinghuysen Ave., 

Newark, N. J. 

P. O. Box 41, Linwood Station, 
Detroit, Mich. 


N. V. Philips, 

Eindhoven, Holland. 

OLIN, N. E. 

126 W. 73rd St., 
New York, N. Y. 


255 Golden Gate Ave., 
San Francisco, Calif. 
PARK, W. C. 
278 N. Fulton Ave., 
Mt. Vernon, N. Y. 
590 HAMILTON St., 
Vancouver, B. C. 

Box 4969 Hoe Ave., 
New York, N. Y. 


100 Gibbs St., 

Rochester, N. Y. 

12 Dongan PI., 

New York, N. Y. 

932 Collingwood Ave., 

Detroit, Mich. 

4552 Camellis Ave., 

N. Hollywood, Calif. 
404 E. 55th St., 

New York, N. Y. 
195 Broadway, 

New York, N. Y. 
66 Sibley St., 

Detroit, Mich. 
WALL, C. R. 
39 Nassau Ave., 

Malverne, N. Y. 

2719 Hyperion Ave., 
Los Angeles, Calif. 

In addition the following applicant was approved by the Board of Governors 
for transfer from the Active grade to the grade of Fellow : 

6625 Romaine St., 
Hollywood, Calif. 




Article I 


The name of this association shall be SOCIETY OF MOTION PICTURE 

Article II 


Its objects shall be: Advancement in the theory and practice of motion picture 
engineering and the allied arts and sciences, the standardizationof the equipment, 
mechanisms, and practices employed therein, the maintenance of a high profes- 
sional standing among its members, and the dissemination of scientific knowledge 
by publication. 

Article III 

Any person of good character may be a member in any class for which he is 

Article IV 


The officers of the Society shall be a President, a Past-President, an Executive 
Vice-President, an Engineering Vice- President, an Editorial Vice-President, a 
Financial Vice-President, a Convention Vice-President, a Secretary, and a Trea- 

The term of office of the President, the Past-President, the Executive Vice- 
President, the Engineering Vice-President, the Editorial Vice-President, the 
Financial Vice-President, and the Convention Vice-President shall be two years, 
and the Secretary and the Treasurer one year. Of the Engineering, Editorial, 
Financial, and Convention Vice-Presidents, two shall be elected alternately each 
year, or until their successors are chosen. The President shall not be immedi- 
ately eligible to succeed himself in office. 

Article V 

Board of Governors 

The Board of Governors shall consist of the President, the Past-President, the 
five Vice-Presidents, the Secretary, the Treasurer, the Section Chairmen, and five 
elected Governors. Two, and three, of the Governors shall be elected alternately 
each year to serve for two years. 

* Corrected to January 1, 1939. 



Article VI 


There shall be an annual meeting, and such other meetings as stated in the By- 

Article VII 


This Constitution may be amended as follows : Amendments shall be approved 
by the Board of Governors, and shall be submitted for discussion at any regular 
members' meeting. The proposed amendment and complete discussion then shall 
be submitted to the entire Active, Fellow, and Honorary membership, together 
with letter ballot as soon as possible after the meeting. Two-thirds of the vote 
cast within sixty days after mailing shall be required to carry the amendment. 

By-Law I 


Sec. 1. The membership of the Society shall consist of Honorary members, 
Fellows, Active members, Associate members, and Sustaining members. 

An Honorary member is one who has performed eminent services in the ad- 
vancement of motion picture engineering or in the allied arts. An Honorary 
member shall be entitled to vote and to hold any office in the Society. 

A Fellow is one who shall not be less than thirty years of age and who shall 
comply with the requirements of either (a) or (6) for Active members and, in 
addition, shall by his proficiency and contributions have attained to an outstand- 
ing rank among engineers or executives of the motion picture industry. A 
Fellow shall be entitled to vote and to hold any office in the Society. 

An Active member is one who shall be not less than 25 years of age, and shall be: 

(a) A motion picture engineer by profession. He shall have been engaged 
in the practice of his profession for a period of at least three years, and shall have 
taken responsibility for the design, installation, or operation of systems or appa- 
ratus pertaining to the motion picture industry. 

(6) A person regularly employed in motion picture or closely allied work, 
who by his inventions or proficiency in motion picture science or as an executive 
of a motion picture enterprise of large scope, has attained to a recognized standing 
in the motion picture industry. In case of such an executive, the applicant must 
be qualified to take full charge of the broader features of motion picture engi- 
neering involved in the work under his direction. 

(c) An Active member is privileged to vote and to hold any office in the 

An Associate member is one who shall be not less than 18 years of age, and 
shall be a person who is interested in or connected with the study of motion 
picture technical problems or the application of them. An Associate member is 
not privileged to vote, to hold office or to act as chairman of any committee, 
although he may serve upon any committee to which he may be appointed; and, 
when so appointed, shall be entitled to the full voting privileges of a committee 


A Sustaining member is an individual, a firm, or corporation contributing 
substantially to the financial support of the Society. 

Sec. 2. All applications for membership or transfer, except for honorary or 
fellow membership, shall be made on blank forms provided for the purpose, and 
shall give a complete record of the applicant's education and experience. Honor- 
ary and Fellow membership may not be applied for. 

Sec. 3. (a) An Honorary membership may be granted upon recommendation 
of the Board of Governors when confirmed by a four-fifths majority vote of the 
Honorary members, Fellows, and Active members present at any regular meeting 
of the Society. An Honorary member shall be exempt from all dues. 

(&) Fellow membership may be granted upon recommendation of at least 
three-fourths of the Board of Governors. 

(c) Applicants for Active membership shall give as reference at least three 
members of Active or of higher grade in good standing. Applicants shall be 
elected to membership by the approval of at least three-fourths of the Board of 

(d) Applicants for Associate membership shall give as reference at least one 
member of higher grade in good standing. Applicants shall be elected to member- 
ship by the approval of at least three-fourths of the Board of Governors. 

By-Law II 


Sec. 1. An officer or governor shall be an Honorary, a Fellow, or Active mem- 

Sec. 2. Vacancies in the Board of Governors shall be filled by the Board of 
Governors until the annual meeting of the Society. 

By-Law III 

Board of Governors 

Sec. 1. The Board of Governors shall transact the business of the Society be- 
tween members' meetings, and shall meet at the call of the president. 

Sec. 2. A majority of the Board of Governors shall constitute a quorum at 
regular meetings. 

Sec. 3. When voting by letter ballot, a majority affirmative vote of the total 
membership of the Board of Governors shall carry approval, except as otherwise 

Sec. 4. The Board of Governors, when making nominations to office, and 
to the Board, shall endeavor to nominate persons, who in the aggregate are 
representative of the various branches or organizations of the motion picture in- 
dustry, to the end that there shall be no substantial predominance upon the Board, 
as the result of its own action, of representatives of any one or more branches or 
organizations of the industry. 

By-Law IV 


Sec. 1. The location of each meeting of the Society shall be determined by 
the Board of Governors. 


Sec. 2. Only Honorary members, Fellows, and Active members shall be en- 
titled to vote. 

Sec. 3. A quorum of the Society shall consist in number of one-tenth of the 
total number of Honorary members, Fellows, and Active members as listed in the 
Society's records at the close of the last fiscal year. 

Sec. 4. The fall convention shall be the annual meeting. 

Sec. 5. Special meetings may be called by the president and upon the request 
of any three members of the Board of Governors not including the president. 

Sec. 6. All members of the Society in any grade shall have the privilege of dis- 
cussing technical material presented before the Society or its Sections. 

By-Law V 

Duties of Officers 

Sec. 1. The President shall preside at all business meetings of the Society and 
shall perform the duties pertaining to that office. As such he shall be the chief 
executive of the Society, to whom all other officers shall report. 

Sec. 2. In the absence of the president, the officer next in order as listed in 
Article 4 of the Constitution shall preside at meetings and perform the duties of 
the president. 

Sec. 3. The five vice-presidents shall perform the duties separately enumerated 
below for each office, or as defined by the president : 

(a) The Executive Vice-President shall represent the president in such geo- 
graphical areas of the United States as shall be determined by the Board of 
Governors, and shall be responsible for the supervision of the general affairs of 
the Society in such areas, as directed by the president of the Society. 

(b) The Engineering Vice-President shall appoint all technical committees. 
He shall be responsible for the general initiation, supervision, and coordination of 
the work in and among these committees. He may act as chairman of any com- 
mittee or otherwise be a member ex-officio. 

(c) The Editorial Vice-President shall be responsible for the publication of 
the Society's JOURNAL and all other technical publications. He shall pass upon 
the suitability of the material for publication, and shall cause material suitable 
for publication to be solicited as may be needed. He shall appoint a papers 
committee and an editorial committee. He may act as chairman of any com- 
mittee or otherwise be a member ex-officio. 

(d) The Financial Vice-President shall be responsible for the financial opera- 
tions of the Society, and shall conduct them in accordance with budgets approved 
by the Board of Governors. He shall study the costs of operation and the in- 
come possibilities to the end that the greatest service may be rendered to the 
members of the Society within the available funds. He shall submit proposed 
budgets to the Board. He shall appoint at his discretion a ways and means 
committee, a membership committee, a commercial advertising committee, and 
such other committees within the scope of his work as may be needed. He may 
act as chairman of any of these committees or otherwise be a member ex-officio. 

(e) The Convention Vice-President shall be responsible for the national con- 
ventions of the Society. He shall appoint a convention arrangements com- 
mittee, an apparatus exhibit committee, and a publicity committee. He may 
act as chairman of any committee, or otherwise be a member ex-officio. 


Sec. 4. The Secretary shall keep a record of all meetings; he shall conduct the 
correspondence relating to his office, and shall have the care and custody of 
records, and the seal of the Society 

Sec. 5. The Treasurer shall have charge of the funds of the Society and disburse 
them as and when authorized by the financial vice-president. He shall make 
an annual report, duly audited, to the Society, and a report at such other times 
as may be requested. He shall be bonded in an amount to be determined by the 
Board of Governors and his bond filed with the secretary. 

Sec. 6. Each officer of the Society, upon the expiration of his term of office, 
shall transmit to his successor a memorandum outlining the duties and policies 
of his office. 

By-Law VI 


Sec. 1. (a) All officers and five governors shall be elected to their respective 
offices by a majority of ballots cast by the Active, Fellow, and Honorary members 
in the following manner : 

Not less than three months prior to the annual fall convention, the Board of 
Governors, having invited nominations from the Active, Fellow, and Honorary 
membership by letter form not less than forty days before the Board of Governors' 
meeting, shall nominate for each vacancy several suitable candidates. The sec- 
retary shall then notify these candidates of their nomination, in order of nomina- 
tion, and request their consent to run for office. From the list of acceptances, 
not more than two names for each vacancy shall be selected by the Board of 
Governors and placed on a letter ballot. A blank space shall also be provided 
on this letter ballot under each office, in which space the names of any Fellows or 
Honorary members other than those suggested by the Board of Governors may 
be voted for. The balloting shall then take place. 

The ballot shall be enclosed in a blank envelope which is enclosed in an outer 
envelope bearing the secretary's address and a space for the member's name and 
address. One of these shall be mailed to each Active, Fellow, and Honorary 
member of the Society, not less than forty days in advance of the annual fall con- 

The voter shall then indicate on the ballot one choice for each office, seal the 
ballot in the blank envelope, place this in the envelope addressed to the secretary, 
sign his name and address on the latter, and mail it in accordance with the in- 
structions printed on the ballot. No marks of any kind except those above pre- 
scribed shall be placed upon the ballots or envelopes. 

The sealed envelope shall be delivered by the secretary to a committee of tell- 
ers appointed by the president at the annual fall convention. This committee 
shall then examine the return envelopes, open and count the ballots, and announce 
the results of the election. 

The newly elected officers and governors of the general Society shall take office 
on the January 1st following their election. 

(6) The first group of vice-presidents, viz., the executive vice-president, engi- 
neering vice-president, editorial vice-president, financial vice-president, conven- 
tion vice-president, and a fifth governor, shall be nominated by the Board of 
Governors at its first meeting after the ratification of the corresponding provisions 


of the Constitution; and the membership shall vote on the candidates in accord- 
ance with the procedure prescribed in these By-Laws for regular elections of 
officers so far as these may be applicable. 

By-Law VII 

Dues and Indebtedness 

$ ec i xhe annual dues shall be fifteen dollars ($15) for Fellows and Active 
members and seven dollars and fifty cents ($7.50) for Associate members, payable 
on or before January 1st of each year. Current or first year's dues for new mem- 
bers, dating from the notification of acceptance in the Society, shall be prorated 
on a monthly basis. Five dollars of these dues shall apply for annual subscription 
to the JOURNAL. No admission fee will be required for any grade of member- 

Sec. 2. (a) Transfer of membership may be made effective at any time by 
payment of the pro rata dues for the current year. 

(b) No credit shall be given for annual dues in a membership transfer from a 
higher to a lower grade, and such transfers shall take place on January 1st of each 

(c) The Board of Governors upon their own initiative and without a transfer 
application may elect, by the approval of at least three-fourths of the Board, any 
Associate or Active member for transfer to any higher grade of membership. 

S ec , 5. Annual dues shall be paid in advance. All Honorary Members, Fel- 
lows, and Active Members in good standing, as defined in Sec. 5, may vote or 
otherwise participate in the meetings. 

Sec. 4. Members shall be considered delinquent whose annual dues for the 
year remain unpaid on February 1st. The first notice of delinquency shall be 
mailed February 1st. The second notice of delinquency shall be mailed, if neces- 
sary, on March 1st, and shall include a statement that the member's name will be 
removed from the mailing list for the JOURNAL and other publications of the Society 
before the mailing of the April issue of the JOURNAL. Members who are in arrears 
of dues on June 1st, after two notices of such delinquency have been mailed to 
their last address of record, shall be notified their names have been removed 
from the mailing list and shall be warned unless remittance is received on or before 
August 1st, their names shall be submitted to the Board of Governors for action 
at the next meeting. Back issues of the JOURNAL shall be sent, if available, to 
members whose dues have been paid prior to August 1st. 

Sec. 5. (a)Members whose dues remain unpaid on October 1st may be dropped 
from the rolls of the Society by majority vote and action of the Board, or the 
Board may take such action as it sees fit. 

(6) Anyone who has been dropped from the rolls of the Society for non-pay- 
ment of dues shall, in the event of his application for reinstatement, be considered 
as a new member. 

(c) Any member may be suspended or expelled for cause by a majority vote 
of the entire Board of Governors ; provided he shall be given notice and a copy 
in writing of the charges preferred against him, and shall be afforded oppor- 
tunity to be heard ten days prior to such action. 

Sec. 6. The provisions of Section 1 to 4, inclusive, of this By-Law VII, given 
above may be modified or rescinded by action of the Board of Governors. 


By-Law VIII 


Sec. 1 . The emblem of the Society shall be a facsimile of a four-hole film-reel 
with the letter 5 in the upper center opening, and the letters M, P, and E, in the 
three lower openings, respectively. In the printed emblem, the four-hole open- 
ings shall be orange, and the letters black, the remainder of the insignia being black 
and white. The Society's emblem may be worn by members only. 

By-Law IX 


Sec. 1 . Papers read at meetings or submitted at other times, and all material 
of general interest shall be submitted to the editorial board, and those deemed 
worthy of permanent record shall be printed in the JOURNAL. A copy of each 
issue shall be mailed to each member in good standing to his last address of record. 
Extra copies of the JOURNAL shall be printed for general distribution and may be 
obtained from the General Office on payment of a fee fixed by the Board of 

By-Law X 

Local Sections 

Sec. 1. Sections of the Society may be authorized in any state or locality where 
the Active, Fellow, and Honorary membership exceeds 20. The geographic 
boundaries of each Section shall be determined by the Board of Governors. 

Upon written petition, signed by 20 or more Active members, Fellows and 
Honorary members, for the authorization of a Section of the Society, the Board of 
Governors may grant such authorization. 


Sec. 2. All members of the Society of Motion Picture Engineers in good stand- 
ing residing in that portion of any country set apart by the Board of Governors 
tributary to any local Section shall be eligible for membership in that Section, and 
when so enrolled they shall be entitled to all privileges that such local Section 
may, under the General Society's Constitution and By-Laws, provide. 

Any member of the Society in good standing shall be eligible for non-resident 
affiliated membership of any Section under conditions and obligations prescribed 
for the Section. An affiliated member shall receive all notices and publications 
of the Section but he shall not be entitled to vote at Sectional meetings. 

Sec. 3. Should the enrolled Active, Fellow, and Honorary membership of a 
Section fall below 20, or should the technical quality of the presented papers fall 
below an acceptable level, or the average attendance at meetings not warrant the 
expense of maintaining the organization, the Board of Governors may cancel its 


Sec. 4. Each Section shall nominate and elect a chairman, two managers, and 
a secretary-treasurer. The Section chairmen shall automatically become mem- 
bers of the Board of Governors of the General Society, and continue in that posi- 
tion for the duration of their terms as chairmen of the local Sections. 



Sec. 5. The officers of a Section shall be Active, Fellow, or Honorary members 
of the General Society. They shall be nominated and elected to sectional office 
under the method prescribed under By-Law VI, Section 1, for the nomination 
and election of officers of the General Society. The word manager shall be sub- 
stituted for the word governor. All Section officers shall hold office for one year, 
or until their successors are chosen, except the Board of Managers, as hereinafter 


$ ec Q The Board of Managers shall consist of the Section chairman, the Sec- 
tion past-chairman, the Section secretary-treasurer, and two Active, Fellow, or 
Honorary members, one of which last named shall be elected for a two-year term, 
and one for one year, and then one for two years each year thereafter. At the 
discretion of the Board of Governors, and with their written approval, this list 
of officers may be extended. 


Sec. 7. The business of a Section shall be conducted by the Board of Managers. 


Sec. 8. (a) As early as possible in the fiscal year, the secretary of each Section 
shall submit to the Board of Governors of the Society a budget of expenses for the 

(b) The treasurer of the General Society may deposit with each Section secre- 
tary-treasurer a sum of money, the amount to be fixed by the Board of Governors, 
for current expenses. 

(c) The secretary-treasurer of each Section shall send to the treasurer of the 
General Society, quarterly or on demand, an itemized account of all expenditures 
incurred during the preceding interval. 

(d) Expenses other than those enumerated in the budget, as approved by the 
Board of Governors of the General Society, shall not be payable from the general 
funds of the Society without express permission from the Board of Governors. 

(e) A Section Board of Managers shall defray all expenses of the Section not 
provided for by the Board of Governors, from funds raised locally by donation, or 
by fixed annual dues, or by both. 

(/) The secretary of the Society shall, unless otherwise arranged, supply to 
each Section all stationery and printing necessary for the conduct of its business. 


Sec. 9. The regular meetings of a Section shall be held in such places and at 
such hours as the Board of Managers may designate. 

The secretary-treasurer of each Section shall forward to the secretary of the 
General Society, not later than five days after a meeting of a Section, a statement 
of the attendance and of the business transacted. 



Sec. 10. Papers shall be approved by the Section's papers committee previ- 
ously to their being presented before a Section. Manuscripts of papers presented 
before a Section, together with a report of the discussions and the proceedings of 
the Section meetings, shall be forwarded promptly by the Section secretary- 
treasurer to the secretary of the General Society. Such material may, at the dis- 
cretion of the board of editors of the General Society, be printed in the Society's 


Sec. 11. Sections shall abide by the Constitution and By-Laws of the Society, 
and conform to the regulations of the Board of Governors. The conduct of Sec- 
tions shall always be in conformity with the general policy of the Society as fixed 
by the Board of Governors. 

By-Law XI 


Sec. 1. These By-Laws may be amended at any regular meeting of the So- 
ciety by the affirmative vote of two-thirds of the members present at a meeting 
who are eligible to vote thereon, a quorum being present, either on the recom- 
mendation of the Board of Governors or by a recommendation to the Board 
of Governors signed by any ten members of active or higher grade, provided that 
the proposed amendment or amendments shall have been published in the JOUR- 
NAL of the Society, in the issue next preceding the date of the stated business meet- 
ing of the Society, at which the amendment or amendments are to be acted upon. 

Sec. 2. In the event that no quorum of the voting members is present at the 
time of the meeting referred to in Sec. 1, the amendment or amendments shall be 
referred for action to the Board of Governors. The proposed amendment or 
amendments then become a part of the By-Laws upon receiving the affirmative 
vote of three-quarters of the Board of Governors. 




Volume XXXII April, 1939 



A Motion Picture Dubbing and Scoring Stage 


Unidirectional Microphone Technic 


Artificially Controlled Reverberation S. K. WOLF 390 

The Evolution of Arc Broadside Lighting Equipment 


Some Studies on the Use of Color Coupling Developers for 
Toning Processes K. FAMULENER 412 

The Metro-Goldwyn-Mayer Semi-Automatic Follow-Focus De- 
vice J. ARNOLD 419 

Independent Camera Drive for the A-C. Interlock Motor 
System F. G. ALBIN 424 

Silent Wind-Machine F. G. ALBIN 430 

New Motion Picture Apparatus 

Characteristics of Supreme Panchromatic Negative 

A. W. COOK 436 
New Background Projector for Process Cinematography. . . . 

G. H. WORRALL 442 

Book Reviews 445 

Current Literature 447 

Officers and Governors of the Society 452 

Committees of the Society 455 

Spring Convention at Hollywood, April 17-21, 1939 460 

Abstracts of Convention Papers : 465 

Society Announcements 480 





Board of Editors 
J. I. CRABTREE, Chairman 




Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 


** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 
** Past-President: S. K. WOLF, RKO Building, New York, N. Y. 
** Executive Vice-President: N. Levinson, Burbank, Calif. 

* Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
** Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 
** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 

* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. J. 

** M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

* H. GRIFFIN, 90 Gold St., New York, N. Y. 

* D. E. HYNDMAN, 350 Madison Ave., New York, N. Y. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

* A. C. HARDY, Massachusetts Institute of Technology. Cambridge, Mass. 

* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 

** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys, Calif. 

* Term expires December 31, 1939. 
** Term expires December 31, 1940. 



Summary. A new dubbing (re-recording) and scoring (music recording) building 
recently completed on the Republic lot consists of a recording stage, scoring monitor 
room, machine room, projection booth, power room, maintenance room, and a recording 
truck testing platform. 

The recording equipment consists essentially of two complete RCA high-fidelity 
recording channels, together with their associated equipment of film recorders, film 
phonographs, amplifier racks, power rectifiers, dubbing and scoring consoles, "ace- 
tate" recorder and projection equipment. 

The stage is of the live-end-dead-end type, and has dimensions which conform to 
the recommended 1:2:3 ratio. The live-end is provided with permanent side wall and 
ceiling reflecting panels which increase the reverberation and diffusion of sound. The 
remainder of the stage is treated with 4-inch rockwool battens, placed between the studs 
and retained in place by a dual muslin covering. The measured reverberation charac- 
teristic of the stage, fulfilling recommended requirements, is between 0.95 and 1 .00 
second for the frequency band of 540 to 7000 cps. The stage is equipped also with an 
eight-position mixer console so that dubbing may be monitored in a room having ap- 
proximate theater sound characteristics. 

Republic's recently completed dubbing (re-recording) and scoring 
(music recording) building was designed and constructed essentially 
for sound recording. The building is located adjacent to the sound- 
cutting building and readily accessible to the film vaults and loading 
rooms. The complete unit (Fig. 1) consists of a recording stage, 
scoring monitor room, machine room, projection booth, power room, 
maintenance room, and recording-truck testing platform. 

When designing the building, acoustical considerations and acces- 
sibility between rooms were given preference. Reinforced concrete 
footings and foundations are used for all walls and supporting columns 
making the building rigid and free from vibration. The stage foot- 
ings and foundation are isolated from those of the remainder of the 
building by a 6-inch space filled with granulated cork. All ground 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 27, 

'** Republic Productions, Inc., North Hollywood, Calif. 
t RCA Manufacturing Co., Hollywood, Calif. 




floors are constructed of fine gravel and sand asphalt laid hot within 
the foundation walls. Asphalt was used in preference to concrete be- 
cause the asphalt has a lower sound- transmission rate and is compara- 
tively non-homogeneous. The walls and roof structure of the work- 
rooms adjacent to the stage are of wood construction. The outsides 

of the walls are covered with 1-inch 
diagonal sheathing and a 1-inch finish 
of exterior cement stucco. The in- 
terior walls are of plaster board and 
cement plaster finish. The ceilings of 
all rooms and the hallway, with the 
exception of the truck- testing plat- 
form, are of plaster board y 2 -inch 
brown plaster finished with 1 / 2 -inch 
"Acoustite" rockwool composition 

Recording Stage. The recording 
stage, which was constructed essen- 
tially as a unit, is 25 feet high, 50 feet 
wide, and 75 feet long, satisfying the 
well known criterion that, for a stage 
of this size, the ratio of height, width, 
and length should be 1 : 2 : 3 . The ratio 
of 2:3:5 for the above dimensions is 
sometimes recommended, but a little 
consideration will quickly show that 
an enclosure of such size will not only 
make an undesirably high ceiling and 
narrowly spaced side walls, but will 
also cause the "mean free path" 
(average length of one reflection) to 
be longer. This condition produces 
fewer reflections per second at any 
point in the room, resulting in de- 
creased diffusion of sound in the room. 

FIG. 1. Plan of buildings. 

Forty musicians represent the optimum number of performers in 
this stage for maximum quality and best illusion, while eighty musi- 
cians represent the largest number that can be crowded into the space 
and still provide reasonably satisfactory recordings. In this connec- 
tion it should be remembered that it is practically impossible to imi- 

April, 1939] 



tate the acoustics of a large room in an enclosure that is actually 
small. On the other hand, the acoustics of a small room can be imi- 
tated easily in a large enclosure by the judicious use of flats and other 
reflecting surfaces. 

Only two materials, rockwool and wood, are used for the interior 
finish of this live-end-dead-end stage. In Figs. 1, 2, and 3, it is seen 
that wood is used as a reflective material around the band-shell (live- 
end) to produce sufficient localized reverberation to permit the musi- 
cians, long accustomed to playing in reverberant concert halls, to keep 
more easily in tune, to determine without undue effort precisely the 
true pitch of the following note while perceiving the present one, and 
to retain proper balance between bass and treble. Wood instead of 

Alltlta" Book Wool Treatment 

FIG. 2. Elevation of stage, monitor room, and projection room. 

some other material such as plaster or hard pressed-board was se- 
lected because of its well liked and practically inimitable quality of 
resonating over a wide range of musical pitch, as evidenced by its use 
in concert halls of avowedly superior acoustics. 

Because of the reverberant character of this band-shell it became 
important to make arrangements for the prevention of echoes and for 
an effective dispersion of the sound to obtain uniform distribution of it 
in the stage. This object was achieved by providing suitably orien- 
tated corrugations of sufficient depth to become effective also as dif- 
fusers of sound for lower frequencies. The absorbent panels at re- 
versed angles to the reflective ones are necessary to prevent the sound 
from being returned into the shell in too great a measure. 

The orientation of the reflective side-wall and ceiling splays is such 
as to obtain not only sufficient localized reverberation in the band- 
shell but also to achieve a desirably directed efflux of the sound into 
the dead end of the stage. Reflecting surfaces close to the perform- 
ers are, therefore, positioned so as to secure enough short- time reflec- 



tions at the microphone to preserve the naturalness of the instru- 
ments, while more distant reflecting surfaces are utilized to produce 
in the band-shell a sufficient amount of the long-time reflections which 
musically are so pleasing and without which the music would tend to 
sound flat, as in the open air. The problem, on close inspection, will 
be found to be exceedingly complex, not only because it is essentially 
three-dimensional in character, but also because not one but many 
sources of sound must be taken into consideration. A solution was 
obtained by drawing many diagrams depicting the travel of sound 

FIG. 3. Interior of recording stage. 

from various parts in the stage and for several angles of splay-slope, 
and then choosing a splay orientation that gave the most desirable 
results for the largest number of considered imaginary point-sources 
representing the musicians. 

The absorbent regions surrounding the microphone, as well as the 
dead end of the stage are, of course, necessary to provide placement of 
sufficient damping material to give the desired reverberation period 
in the stage and to permit the smoothing out of whatever interference 
pattern may exist there. Interference, it is well known, may be of 
the nature of a space or a time-effect. The first enters most clearly 
during sustained passages, when the transmitter may be at a region of 

April, 1939] 



reduced or enhanced sound-intensity. The time-effect makes itself 
known in the form of irregular fluctuations of the sound-pressure dur- 
ing growth or decay of the sound in the room. The more reverberant 
a room, the more pronounced are the two effects, and the more dis- 
turbing do they appear in a recording. 

*" .6 





\OO 1.000 10.000 


FIG. 4. ( Upper) Reverberation-volume curve. 
5. (Lower) Republic stage reverberation-frequency 

Recording studios should have a reverberation- time at 1000 cycles 
of about two-thirds of that found satisfactory for a room of equal vol- 
ume used for binaural hearing. Fig. 4 shows the limits of variation 
of reverberation time with volume for scoring stages, and illustrates 
that it is not readily possible to speak of the optimal time of rever- 
beration of a room as a definite figure unless one mentions at the same 
time the type of activity for which the room is being used, such as for 
speech, piano recitals, or songs. The optimal time, in general, is 
therefore a range, with the upper limit pertaining to organ oratoria 


and the lower limit to speech. A mean value of reverberation at 
1000 cycles of 0.97 second was chosen as being the time most suitable 
for the type of music to be most frequently played on this stage. A 
number of portable hinged panels, 4 by 7 feet, absorbent on one side 
and reflective on the other, are used to provide acoustical isolation or 
special reverberation effects for small groups of performers. 

The variation of reverberation time with frequency, called the 
reverberation characteristic, has been widely discussed in the litera- 
ture. 1 ' 2 - 3 - 4 However, none of the criteria so far proposed for the re- 
verberation characteristic in rooms appears to be completely tenable 
for scoring stages. Even MacNair's criterion,* which for the lower 
frequencies makes for reverberation-times shorter than those ob- 
tained by any other criterion, when applied to a scoring stage still 
produces recordings marred by a little "boominess." Fig. 5 shows the 
reverberation characteristic of this scoring stage, and all tests made 
so far direct listening tests as well as recording tests show that the 
studio is remarkably free from any boominess or prolonged reverbera- 
tion for the lower frequencies. 

It may be of interest to determine for this stage the value of the 
M. O. Strutt equation for the ratio of the "useful" to delayed sound. 
By "useful" sound is meant the direct sound plus that sound that 
comes to an auditor within Vie second after it was emitted; by de- 
layed sound is meant the sound that comes to an auditor Vie second 
after it was emitted. The value of this equation depends, of course, 
on the distance between the auditor and the source of sound ; for this 
purpose an average distance D equal to V 1 /3 /2 ( V = volume of stage) 
was chosen. The M. O. Strutt 5 equation is: 

+ / e -13.8t/Tdt 

-i3.8//r dt 

where P = power output of source of sound. 
c = velocity of sound. 

T = time of reverberation (the reverberation time for a given frequency 
is the time required for the average sound-energy density, initially in 
a steady state, to decrease, after the source is stopped, to one-mil- 
lionth of its initial value). 

* By this criterion the loudness level of all frequency components in speech 
and music should decay at the same constant rate. 


V = volume of room. 
t = time. 

D = distance between source of sound and position of listener or micro- 

This equation may be written as : 

Q -0.86 [-0.004 y/ -nix 
e T L r J 

if r = 1 second, V = 90,000 cubic-feet; Q equals 1.78, showing that 
the amount of "useful" sound is quite large at this average distance 
of 90,000' /3 /2 or 22.5 ft. 

All construction in the stage was made exceedingly rigid to avoid 
structural resonances. The wall-studs are 2 by 6 inch, covered on the 
outside with 1-inch diagonal sheathing and 1-inch exterior cement 
stucco. The entire wall area in the dead-end half is treated with 4- 
inch long-fiber rockwool battens placed between the studs and held 
in place by a retaining layer of 40-44 muslin stapled to the interior 
side of the studs (Fig. 8) . On top of this layer of muslin, 1 by 2-inch 
wood retaining strips are nailed at right angles to the studs. The 
strips are spaced on 9-inch centers from the floor to a 5-ft. height. 
From this point the spacing is graduated from 18-inch centers to 12- 
inch centers at the plate line. On top of the wood strips, a layer of 
fire-proofed and color-dyed muslin is tacked. The tacks and muslin 
joints are covered with 3 / 4 -inch wood half-round. Fig. 3 shows the 
finished appearance of the absorbent treatment. 

The roof of the stage consists of a Lamella roof resting on 8 by 10-in. 
sills anchored to the 2 by 6-in. side walls. The crown of the roof is 
approximately 34 x /2 feet above the finished floor. The roof sills are 
tied together by four \ l / z -in. steel tie-rods to absorb the roof thrust. 
The Lamellas consist of segments of an arc milled so as to intersect 
continuously and uniformly as the "skew arch" crosses the roof. 

These intersecting arches (Fig. 6) form the familiar diamond pat- 
tern of the Lamella roof. Each diamond in the stage is 8 feet long and 
36 inches wide, with each intersection joint bolted with one 5 /g-inch 
bolt. The diamond-patterned Lamella roof is used to carry the center 
43-ft. section of the roof with diagonal sheathed rafters closing the 16- 
foot end-sections, and spanned from the end-walls to the end arch of 
the Lamella web. 

The height of the roof from the floor, the high degree of fire resis- 
tance, the absence of intermediate supports for the roof, and the free- 
dom from large structural members requiring sound-deadening treat- 
ment were all factors guiding the selection of the roof as the best 



suited for this modern recording stage. The entire roof area is acous- 
tically treated with 4-inch rockwool battens (Fig. 6) in the same man- 
ner as the wall area with the exception of the spacing of the retaining 
strips, which is graduated from 26 inches at the sill line to 8 inches at 
the center of the ceiling. 

The interior of the live-end wall area of the stage is covered with 1- 
inch fiber insulation board. The reflective side-wall splays (Figs. 1, 

FIG. 6. Roof construction and treatment. 

2, 3) reaching from floor to ceiling consist of alternate wood panels 
parallel to each other and separated by angular absorbing panels 2 
feet in width. The panel construction consists of 2 by 6-inch studs 
and cross-pieces, spaced on 2-ft. centers covered with 1-inch diagonal 
sheathing surfaced with 3 /Vinch grooved T & G ceiling lumber. The 
rear of the panels is braced at 6V2-ft. intervals to the wall of the stage. 
Eight 35-ft. angular ceiling splays (Fig. 3) are anchored to the ceiling 
between the side-wall panels. These panels are of 1-inch plywood 
lumber, screwed to 2 by 12-in. supporting joists and cross-pieces 

April, 1939] 



spaced on 2-f t. centers and bolted to the roof rafters. The surfaces of 
all wood panels are stained and finished with three coats of trans- 
parent varnish. 

The stage floor consists of 2 by 6-in. joists laid flat on the 4-inch 
asphalt ground floor. The space between the joists is filled to the 
surface with fine aggregate asphalt. A subfloor of 1-inch T & G di- 
agonal sheathing is securely nailed to the joists. A 1-inch T & G- 
finished floor is nailed directly on top of the sheathing. This con- 
struction results in a very rigid non-resonant type of floor. 






I"X3" OAK 



FIG. 7. Detail of sound retarding doors. 

A horn-tower (Figs. 1, 2) 6 feet wide by 9 feet long is provided in 
back of the projection screen. The interior walls and ceiling of the 
horn-tower are treated with 4-inch rockwool battens. The horn- 
tower floor, which is 6 feet above the stage floor, is of wood construc- 
tion covered with 1-inch fiber insulation board. Entrance to the 
tower is through a trap-door in the floor. The sound-reproducing 
system is the well known RCA two-way loud speaker system em- 
ploying two high-frequency and four low-frequency units. The 
width of the horn-tower allows only a 4-inch space between the low- 
frequency units and the side wall. This space and the area around 
the high-frequency speaker is closed in with 1-in. fiber insulation 
board. This construction prevents the generation of backstage reso- 
nance in the loud speaker cavity. 


All openings leading into the stage are closed with massive double 
doors made of dual sections of 1-inch plywood, 1-inch insulation 
board, and 18-gauge sheet-metal, as shown in Fig. 7. The doors are 
held tightly closed against rubber weather-stripping by special non- 
slipping clamps. 

Recording wiring for scoring activities terminates on the stage in 
conveniently located panels consisting of a 6-position microphone 
outlet panel, head-phone outlet panel, signal-light panel, and mobile 
acetate recorder-outlet panel. The music director's stand is equipped 
with a built-in PA microphone, speaker, and head-phone volume con- 
trol. A general PA speaker is mounted on the rear wall of the stage. 

FIG. 8. Republic dubbing console. 

The stage is used also as a monitoring room for dubbing. For this 
purpose an 8-position mixer console is located in the dead end of the 
stage, as shown in Figs. 1 and 3. The dubbing console (Fig. 8) will 
seat three mixer operators, and is designed with a group of special 
equalizer controls located in the center of the console. High-, low-, and 
middle-frequency attenuation and equalization, with the various 
telephone, PA, and special equalizers are provided. Eight single- 
stage booster amplifiers, used with the equalizers, are mounted in the 
console, and are accessible through panels in the side or rear. A 
variable high-pass filter is included with five cut-off frequencies be- 
tween 80 and 150 cycles. Telephone, PA, and signal facilities con- 
necting with all stations, are located within easy reach of all the 

April, 1939] 



Jack bays provide connections to the machine room amplifier bays, 
scoring console, and for patching a reproducer through any desired 
equalizer in any mixer position. A neon volume indicator and an 
electric clock are mounted in the line of screen vision on the front of 
the console. Three remote controls for changing the location of the 


FIG. 9. Detail of monitoring room; stage obser- 
vation window. 

"breakaway point" (post) of the electronic compressor amplifiers are 
installed conveniently near the dialog mixer. Remote volume con- 
trol of the projection reproducing system is provided on the console. 
A projected footage counter is placed below the picture screen, and a 
reset button is located on the dubbing console. 

Scoring Monitor Room. Special consideration was given to the de- 
sign of the scoring monitoring room, which is usually a small room 
ranging in volume from 500 to 5000 cubic-feet. Adjunct to a more 


voluminous and expensive stage, they do not always receive the same 
attention during the design period that the larger enclosure receives, 
and often are accorded only such space as fits in conveniently with the 
grounds. They are important rooms, however, since arrangement of 
orchestra and tonal balance are usually regulated by the mixer in 
these rooms. 

It is well known that enclosures, the dimensions of which are not 
large compared with the wavelength of the sound, exhibit a phenome- 
non known as room resonance. Under such condition one or more 
of the lower modes of vibration of the room may be prominently 
stimulated, causing intensification of the low-frequency components 
of the sound emanating from the monitoring speaker. It is often 
thought that by providing irregularities in the room, such as pilasters 
or corrugations, or by making the enclosure non-rectangular, room 
resonance can be eliminated. Such, of course, is not the case. It is 
more difficult to determine theoretically the frequencies of the eigen- 
tones or damped free vibrations in a non-rectangular room, but the 
number of them occurring within a certain frequency-interval is cer- 
tainly not increased. For that reason, also, cubical rooms, or even 
rooms having two dimensions alike, are less to be recommended than 
oblong rooms, since their eigentones may superimpose, causing an 
even greater intensificiation of a certain frequency in the room. It 
is the number of resonant vibrations within a given frequency band 
that is important in a room, since the larger this number the more 
will every forced vibration in that interval coincide with a natural 
mode of vibration of the room. If the room is not too small, one can 
calculate the number of eigentones within a band by the Rayleigh- 
Jeans formula 6 for the optical case. This is : 

where F = frequency. 

V = volume of room. 

c = velocity of sound. 

N = number of eigentones in the interval ranging from F to F + A F. 

This equation shows that the number of eigentones within a certain 
frequency-band is proportional to the volume of the room, so that 
pilasters, corrugations, etc., exert no effect in changing this number 
except so far as the room is made smaller by them an undesired con- 

April, 1939] 



For this reason the scoring monitoring room, of 4500 cubic-feet 
volume, was kept rectangular in shape with dimensions of 9 feet high, 
18 feet wide, and 28 feet long (ratio 1:2:3) (Figs. 1, 2). The moni- 
toring room floor is covered with a hair-felt pad and a heavyweight 
broadloom carpet. The walls are treated with 1 /z-inch fiber insula- 
tion board applied directly over 1 inch of cement plaster. The ceiling 
is of plaster board, 1 /2-inch brown plaster finished with 1 / 2 -inch 
"Acoustite" plaster. 

Another important property of a monitoring room is adequate 
sound insulation between it and the adjoining studio. The wall ad- 
jacent to the stage is structurally separated from the stage wall and is 


FIG. 10. Diagram of scoring mixer. 

supported by a separate footing. The matter of sufficient insulation 
through the observation window deserves particular attention. 
Such windows often consist of two panes of glass separated by a small 
air space (1 to 3 inches) with one sheet of glass sometimes thicker 
than the other. Work by J. E. R. Constable 7 has shown that such 
an arrangement is invariably less insulative for the lower frequencies 
than a single pane having the combined thickness of the two panes. 
Increased insulation by means of two sheets of glass is achieved only 
if the panes are at least 4 inches apart, and when the wall space be- 
tween the panes is treated with a sound-absorbing material such as 
fiberboard or acoustic plaster. 

The observation window (Fig. 9) for this monitoring room consists 
of two double panes of y 4 -inch plate-glass, with one pair inclined to 
the other at a small angle and the pairs separated from each other as 



shown. The wall space between the pairs of sheets is treated with 
V2-inch nberboard, and the rebate around the edges of the pane is 
closed tightly against the pane with weather-stripping between rebate 
and glass. 

The equipment in the scoring monitoring room consists of a 6-posi- 
tion mixer console and a RCA two-way theater loud speaker system. 
The mixer circuit (Fig. 10) utilizes a switching arrangement for di- 
viding the six mixers into two groups of three, connected to two sepa- 
rate recording channels. A soloist and an orchestra accompaniment 
if isolated with acoustic baffles can be recorded simultaneously on two 
separate films. Whenever the channel is used as described, the scor- 
ing monitor is connected to both recording systems. A neon volume 

FIG. 11. Amplifier rack; Bays 1 to 7. 

indicator and a high-speed Weston meter volume indicator are used as 
level indicators. High- and low-frequency attenuation is supplied in 
four mixer positions. A patch bay is furnished with the necessary 
trunks to the dubbing console amplifier bays and associated equip- 

A signal and PA panel is provided with the additional feature of a 
separate PA switch connecting directly with a PA microphone and 
speaker on the music director's stand enabling the mixer to converse 
privately with the music director. A remote variable jEZ"-pad control 
(Figs. 13, 15) is provided to raise or lower the "breakaway point" of 
No. 4 compressor amplifier (post) used in the scoring channel. A 
reset button for the projected footage counter is conveniently located 
on the console. 

April, 1939] 



Ventilation and Heating. The ventilating and heating system con- 
sists of niters, fan, and gas heater all mounted on cork insulation pads 
on the roof adjacent to the projection room. In order to reduce wind 
noises and fan vibration, a fan normally rated at 20,000 cfm. is 
driven at a speed to produce 6000 cfm. The duct leading from 
the heater to the discharge into the rooms, is lined with 2-inch rock- 
wool blankets, the surface of which is covered with a double thickness 
of 40-44 muslin. Staggered acoustic absorbing panels of 2-inch rock- 
wool are placed at right angles to the air travel at 2-ft. intervals 
throughout the length of the duct. 
The discharge openings from the 
monitoring room and stage are 
designed so that the maximum 
velocity of the air does not exceed 
300 feet per minute. To prevent 
external noise from entering the 
room, acoustic insulating panels of 
1 /2-hich fiber insulation board are in- 
stalled at right angles to the air-flow. 

Machine Room. The machine 
room (Fig. 1) contains the amplifier 
racks, recorders, film phonographs, 
sound-heads, and portable acetate 
recorder. Two complete recording 
channels are provided either for 
scoring or dubbing. There are 
eight amplifier bays containing the 
following equipment : 

Bay No. 1 (Fig. 11) contains six 
microphones and eight photocell 

pre-amplifiers mounted in the upper portion of the rack. The micro- 
phone pre-amplifier is a two-stage amplifier with an overall gain of 
47 db. at 1000 cycles. The first stage of this amplifier utilizes the 
new RCA 1603 tube, 8 fed by a specially designed input transformer. 
Equalization for film-transfer losses is incorporated in these pre- 
amplifiers and consists of a rising characteristic starting from 1000 
cycles and rising to 6 db. at 6000 cycles. The phototube pre-ampli- 
fier is also a two-stage amplifier using the RCA 1603 in the first stage. 
The overall gain is 43 db. at 1000 cycles. Equalization for re-record- 
ing transfer-losses is incorporated in these pre-amplifiers. Both types 

FIG. 12. Mountings for micro- 
phone and phototube pre-amplifiers. 



of pre-amplifiers are mounted in rectangular cases which fit in shelves 
at the rear of the rack (Fig. 12). The male output receptacle at one 
end of the amplifier case connects with the female receptacle on the 
rack, and the input receptacle on the amplifier is connected by a 
short piece of cable from the rack. Power switches, metering jacks, 
and meter are supplied on the front face of the rack. 

A section of jack rows, immediately below, contains high- and low- 
level trunks to the dubbing and scoring consoles, the circuit-test lab., 
the inputs and outputs of two electronic compressor amplifiers, and 
the fixed pads and variable controls associated with the operation of 









: w 










































" c s: 


OR f 
1 &[ 


V ft 








7 D 






o 3 





R M 

2R N 

> SEC. 






.11 / 

k.1 A 3 





FIG. 13. Compressor curves. 

the compressors. The compressors and pads are mounted below the 
jack rows. 

Compressor amplifier No. 1 is designed to work in the music-dub- 
bing channel. The compressor consists of a two-stage push-pull am- 
plifier, the first stage of which is a pair of variable-mu tubes 6K7, the 
gain of which is controlled by the output of the rectifier (6H6). 
The rectifier is fed by a one-stage amplifier (6C5) which is bridged 
across the output of the compressor. The harmonic distortion intro- 
duced by the compressor at an output of plus 10 db. is less than 1 per 
cent. The frequency-response is flat within plus or minus l /z db. 
from 30 cycles to 10,000 cycles. The timing characteristics used in 
this compressor are two milliseconds for operating and approximately 
100 milliseconds for release. The operating characteristic is such 


that it requires a 17-db. increase of input to raise the galvanometer 
the final 3 db. of modulation (curve B, Fig. 13). This compressor is 
operated in this manner to prevent peak voltages from overloading 
the sound-track without affecting the normal volume changes in the 

No. 2 compressor amplifier is designed to work in the dialog dub- 
bing channel (Fig. 14). The timing characteristics used are 2 milli- 
seconds for operating and approximately 500 milliseconds for release. 
The operating characteristic is such that it requires a 20-db. increase 
of input to raise the galvanometer the final 10 db. of modulation, as 
illustrated by curve A of Fig. 13. A variable T-pad in 1-db. steps in 
the output of the compressor is provided on the dubbing console and 
is used to raise or lower the "breakaway point." 

Bays Nos. 2 and 3 (Fig. 11) each contains a complete recording 
amplifier channel with a balanced low-pass filter, 45-cycle high-pass, 
recording amplifier, and d-c. bridging amplifier (Figs. 14 and 15). 
The balanced low-pass filter has variable cut-off frequencies. Speech 
recording is done with the 6500-low-8000, and music recording with 
the 8000-low-10,000. The 45-cycle high-pass with operating charac- 
teristics of 40-high-60 is inserted in the recording channel for both 
music and speech recording. 

The 108 recording amplifier is used as the main gain-amplifier and 
serves to bring the signals from the low-level mixer circuits to a zero 
level at the bridging bus. It employs four stages of amplification 
and has an overall gain of 84 db. at 1000 cycles. The frequency- 
response is flat from 30 cycles to 10,000 cycles, within l / z db. A 
third compressor, which has the operating characteristics of compres- 
sor No. 1, is inserted between the 108 amplifier output and the bridg- 
ing bus, preventing excessive peak voltages from overloading the 
galvanometer. A three-stage bridging amplifier completes the cir- 
cuit between the bridging-bus and the galvanometer. The overall 
gain of this amplifier is 40 db. The frequency response is flat from 30 
cycles to 10,000 cycles within y 2 db. All these amplifiers are pro- 
vided with metering jacks and a meter for measuring operating volt- 

Jacks are provided in both bays for the input and output of each 
individual amplifier and its associated equipment and also high and 
low-level trunks to the different bays and the dubbing and scoring 
consoles. The noise level of the overall channel at the recording gal- 
vanometer is maintained to 60 db. below "O" db., and the overall 



distortion at 400 cycles is 0.4 per cent at 100 per cent galvanometer 

Bay No. 4 (Fig. 11) is the circuit-test lab. and contains an oscilla- 
tor, distortion-factor meter, gain set, and a patch-bay containing 


FIG. 14. ( Upper) Diagram of dubbing channel. 
FIG. 15. (Lower) Diagram of scoring channel. 

trunks to all bays. The jack bay provides connections to various 
loss pads, transformers, band-pass niters and trunk terminations use- 
ful in making transmission runs. A test-panel at the lower section of 
the bay is directly connected to a test-panel in the truck-testing 

April, 1939] 



platform with high- and low-level trunks. It also contains power- 
supply and provision for checking pre-amplifiers. Connections for a 
portable PA system or a telephone hand-set are provided for com- 
munication between the truck platform, maintenance room, and cir- 
cuit lab. 

Bay Nos. 5 and 6 (Fig. 11) contain the monitoring amplifiers and 
associated equipment used with the scoring and dubbing channels. 
Each monitor system consists of a 40-watt amplifier fed by a three- 
stage bridging amplifier the input of which is connected across the 
bridging bus. The monitoring equalization is connected between 
these two amplifiers. The bridging amplifier is similar in operating 

FIG. 16. Noise reduction amplifier Bay 8, recorders, 
and motor switching panel. 

characteristics to those described in Bays 2 and 3. The output of 
the power amplifier feeds the two-way speaker system through its 
dividing network. The total harmonic distortion in the monitoring 
system is less than 1 per cent at a power output of 40 watts. 

Bay No. 7 (Fig. 11) contains the PA amplifiers and signal systems. 
The PA system includes 5 stations: viz., recorder No. 1, recorder No. 
2, scoring console, dubbing console, and projection room. 

Two voltage and two power-amplifiers supply amplification for the 
PA system. A PA switching panel is provided for making the con- 
nections to and from the selected stations. A signal patch panel 
makes it possible to select any station for controlling the signal and 
warning-light system. A portable PA amplifier is provided for use 
with a portable PA microphone and speaker which can be used for 


test communication. A patch-bay is furnished containing the inputs 
and outputs of these amplifiers with trunks to the other bays. 

Bay No. 8 contains the noise-reduction amplifiers (Fig. 16) asso- 
ciated with the recording channels, mounted between the two record- 
ing machines. These noise-reduction amplifiers contain new de- 
velopments in operating characteristics. The timing characteristics 
used are 19 milliseconds opening and approximately 220 milliseconds 
closing. The frequency characteristic of the amplifier is flat from 30 
to 10,000 cycles within l / 2 db. 

A meter and metering jacks are provided for measuring operating 
voltages. A patch-bay is furnished with the inputs and outputs of 
the amplifiers and trunks to the circuit lab. and recording-channel 
bays. This rack contains also an RCA modulated oscillator for use 
in determining optimum negative and printing densities for processing 
control. 9 

The machine room also contains three film-phonographs, five 
sound-heads, two film-recorders, and mobile acetate recorder. The 
three film-phonographs are of the RCA magnetic-drive type and are 
used for reproducing master dialog and music tracks. The five 
sound-heads are of the RCA rotary-stabilizer type, and are used for 
sound-effects tracks. A loop arrangement is mounted above the 
sound-heads providing for film loops up to 300 feet in length. All 
reproducers are equipped with switches for reproducing either stand- 
ard or push-pull tracks. Automatic motor-driven rewinds are fur- 
nished on all reproducers so that it is unnecessary to remove the film 
from the machines for rewinding. An inspection bench is provided 
with motor-driven rewinds and illuminated inspection plates. 

In the rear of the machine room is a panel with outlet for a mobile 
"acetate" recorder which is self-contained in a steel cabinet mounted 
on pneumatic tires. The mechanism is provided with both selsyn 
and synchronous motors driving the turntable at a speed of 78 rpm. 
An RCA 72A cutting mechanism, the new RCA pick-up, tone-arm, 
associated filters and equalizer, microscope, and record-spotting mecha- 
nism complete the operating accessories. The amplifying equip- 
ment consists of an amplifier system and associated filament rectifier. 
A meter volume-indicator is provided in the cutter circuit. The 
external speaker is the new RCA all-metal exponential horn with a 
power handling capacity of 24 watts. A microphone input is fur- 
nished so that the mobile unit may be used as a PA system on the pro- 
duction set. For immediate playback purposes when operating with 


the recording channel, a switch on the acetate control panel operates 
a relay connecting the acetate reproducer and network to the moni- 
toring two-way horn system in both the scoring stage and scoring 
monitoring room. 

Two RCA ultraviolet film recorders of the magnetic-drive type are 
equipped with a photographic slating device and film-punch operated 
simultaneously by a hand-lever. An exposure meter, corrected 
for temperature variations and which gives accurate photometric 
readings for controlling exposure, is mounted on the front of the opti- 
cal systems. The recorders are mounted on tables (Fig. 16) the 
front of which contains a control panel with a PA microphone, tele- 
phone hand-set, interlock control switches, signal-control switches, 
and signal lights. 

Alongside the recording tables on the front wall (Fig. 16) is the 
selsyn distributor control panel which contains twelve specially de- 
signed six-pole double-throw switches, enabling the operator to 
switch any or all of the reproducer and projection interlock motors 
from one distributor to the other. A convenience outlet is installed 
near each reproducer to provide a connection for variable-speed shots. 
A remote portable variable-speed control is provided for operation 
near the dubbing console. 

Projection Booth. The projection room, which is located above a 
section of the hallway and one end of the monitor room (Figs. 1, 2) 
is supported by columns which are structurally separated from the 
stage and the monitor room walls and ceiling. The projection room 
floor consists of a 2-inch layer of asphalt on top of which is 
cemented IVVinch cork insulation pads. One-quarter inch cork 
carpet is cemented to the top of the cork pads. This construction 
eliminates the possibility of footfalls being heard in the monitoring 
room and stage. The ceiling and the upper 3 feet of the projection 
room walls are finished with y 2 -in. "Acoustite" plaster. 

The projection booth contains two Simplex E-7 projection heads 
with removable aperture plates, two high-intensity Peerless Magnarcs 
and RCA PG118 double sound-head projection system with one head 
driven by a synchronous motor and the second head by a selsyn mo- 
tor, and two RCA preview attachments. Both heads are push-pull 
or standard. Each arc lamp is supplied by a General Electric cop- 
per-oxide rectifier of 65-ampere capacity. The amplifier rack con- 
tains a patch-bay with the inputs and outputs of the voltage and 
power amplifiers, and trunk lines to the dubbing and scoring consoles 


and the amplifier bays. A volume indicator meter is mounted on the 
panel and is connected by a switch and transformer across the output 
to the stage speakers to check the level and make frequency runs. 
The photocell output of either sound-head can be plugged into photo- 
cell pre-amplifier No. 9 Bay 1, in the machine room, through a 5-pin 
Cannon receptacle mounted on the wall in front of the sound-heads. 
A signal telephone and PA panel are mounted on the wall between 
the two projectors. A PA and monitor speaker are mounted in the 
end of the booth. A motor-driven rewind cabinet, a film-storage 
cabinet and an inspection table with hand rewinds completes the 
equipment. On the rear wall is a remote switch which turns on all 
the rectifiers in the power room supplying the projection amplifiers, 
exciter lamps, and field supplies. A table-switch on each projector 
controls the relay supplying alternating current to the arc rectifiers. 

Power Room. The power room contains all the rectifiers supplying 
the filament and plate voltages of all recording and reproducing am- 
plifiers, exciter lamp supplies, and field supplies. Two selsyn dis- 
tributors and an emergency truck-battery charging generator are also 
located in the power room. Control panels, starting relays, and all 
associated switches are mounted conveniently on the wall. The 
rectifiers are mounted in specially built racks on one side of the power 
room, and all the wiring is contained in easily accessible gutters. 
Telephone or a portable PA outlet provides communication to the 
truck platform, maintenance room, projection booth, and machine 

Maintenance Room. The maintenance room (Fig. 1) contains a 
work-bench along two side-walls, with cupboards, drawers, and cabi- 
nets for storing accessories and spare parts. A test and patch-panel 
is located above the work-bench with filament and plate supply for 
any amplifier tests and high and low-level trunks to the truck plat- 
form and the circuit lab. telephone; and portable PA communication 
with the truck platform, machine room, projection booth and power 
room, is available. Selsyn interlock and 220- volt 3 -phase connections 
are furnished for testing motors. A complete complement of testing 
instruments, meters, and accessories is provided for all testing. 

Recording Truck Platform. The truck platform contains stalls for 
four sound trucks. In each stall is a 220-volt 3-phase outlet for sup- 
plying the tungar battery-chargers in each truck. Each stall con- 
tains a 16- volt and an 8- volt d-c. charging outlet, supplied by a 
generator in the power room for giving the 16- and 8- volt batteries in 


the sound- trucks an emergency boost charge. In the center rear wall 
of the truck platform is a test-panel with facilities for making audio, 
continuity, and megger tests of all cables used. A patch-bay in the 
test-panel provides high- and low-level lines to the maintenance room 
or the circuit test lab. Thus any truck amplifier can be patched to 
the circuit- test lab. for frequency runs. Telephone or portable PA 
communication is provided between the sound-trucks or the truck 
test-panel, maintenance room, power room, and circuit- test lab. 


1 RETTINGER, M.: "Note on Reverberation Characteristics," /. Acoust. Soc. 
Amer., VI (July, 1934), No. 1, p. 51. 

2 KNUDSON, V. O.: "Recent Developments in Architectural Acoustics," Rev. 
Modern Physics, VI (Jan., 1934), No. 1, p. 14. 

3 RYRING, C. F.: "The Reverberation Time in Dead Rooms," /. Acoust. Soc. 
Amer., 1 (1930), No. 2, p. 217. 

4 MACNAIR, W. A.: "Optimum Reverberation Time for Auditorium," J. 
Acoust. Soc. Amer., 1 (1930), No. 3, p. 242. 

6 STRUTT, M. J. O.: "Raumakustick." Handbuck der Experimental physik 
von Wien-Harms, Bd. 17, Techn. Akustick (1934), S. 460. 

JEANS, J. H.: "On the Partition of Energy between Matter and Ether," 
Phil. Mag., 10 (1905), No. 91. 

7 CONSTABLE, J. E. R. : Phil. Mag., 18 (1934), No. 7, p. 321. 

8 HOLLANDS, L. C., AND GLOVER, A. M. : "Vacuum Tube Engineering for Mo- 
tion Pictures," J. Soc. Mot. Pict. Eng., XXX (Jan., 1938), No. 1, p. 42. 

9 BAKER, J. O., AND ROBINSON, D. H.: "Modulated High-Frequency Record- 
ings as a Means of Determining Conditions for Optional Processing," /. Soc. Mot. 
Pict. Eng., XXX (Jan., 1938), No. 1, p. 3. 


MR. MACNAIR: The expression "closing time" is used with respect to the 
compressor. Exactly what does that mean? 

MR. WOLFE : A more nearly correct term would be "restoring time." What was 
meant was obviously the time required for the gain of the compressor to restore 
to its normal conditions. The term "closing time" was borrowed from noise- 
reduction terminology. 

MR. MACNAIR: Sooner or later, in working with noise-reduction units and 
compressors, we must agree on these terms. Theoretically, the circuit never 
restores except in an infinity of time, and some of us choose to talk about 1/e, 
because we used to be scientists. Others talk about the 99-per cent point, and so 
on. I think sooner or later we must agree on something. 

MR. WOLFE : In our company we are trying to standardize on the 90-per cent 
point, as the point at which the restoring or closing time is measured. 

MR. KELLOGG: I have often wondered what difference in impression you get 
in a small room as compared with a large room if both of them have the same 


reverberation time for all frequencies. That is theoretically quite possible, and 
no doubt it is quite often moderately well approached. I do not believe many of 
us would be fooled into thinking we had a larger room, but I have never seen the 
point brought out quite as well as I think the authors do. 

The authors mention the fact that the small room has a shorter mean free path 
for the sound, and therefore the echoes come much more frequently. You get 
many more echoes in the same time, and if the absorption is adjusted so the total 
reverberation time is the same, then the dying away of the sound takes place in 
smaller jumps. In other words, the sound is chopped up a great deal finer. 

It is of some interest that with a large orchestra we seem to want the rather 
slower chopping that we can get with the large room. With a smaller 
orchestra it is obvious that since there are fewer instruments you might need 
more chopping up of the echoes. In other words, the large number of players 
does very much in one way what the frequent echoes do in the other. That may 
have something to do with our preference for a large room where we have a large 
number of players. 

MR. BUTLER: I believe distribution of frequency in a room is the answer to 
Mr. Kellogg's question. If we have a definite reverberation from one end of the 
room to the other and can distribute it, it is all right; but if we can distribute the 
frequent small echoes, I feel we would have a better overall condition. 



Summary. After describing the constructon of a unidirectonal microphone several 
desirable factors are discussed connected with the use of such a transmitter for recording 
sound in motion picture studios. Six illustrations show how the microphone may be 
used to advangate under specific set conditions, and four diagrams illustrate its use 
in recording various types of music. 

A unidirectional microphone is a microphone that is operated 
partly by sound pressure and partly by a pressure gradient, or differ- 
ence, in sound pressure between the two sides of the part so driven. 
The moving element in the most commonly used unidirectional micro- 
phone is a light corrugated metallic ribbon suspended in the magnetic 
field of a permanent magnet and divided into two parts. One section, 
freely accessible to air vibrations from both sides, acts as a so-called 
velocity microphone, because the induced emf . in the ribbon is, within 
practical limits, directly proportional to the particle velocity of the 
driving sound-wave. The other section of the ribbon, exposed to 
pressures from sound-waves on one side only, has its other side termi- 
nated into an acoustic labyrinth, and responds as a pressure-operated 
device, the induced emf. in the ribbon being proportional to the 
pressure of the driving sound-wave. Because the ribbons are in 
series, the combined output from the microphone is 

E u = E p + E v cos8 (1) 

where E u = Voltage output of the unidirectional microphone for sound origi- 
nating in the direction 6. 

E p = Voltage output of pressure-driven element for sound originating 
in any direction. 

E v = Voltage output of pressure-gradient element for sound originating 
in the direction 6 = 0, which corresponds to the direction of a 
normal to the flat part of the ribbon. 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received September 
23, 1938. 

** Columbia Pictures Corp., Ltd., Hollywood, Calif. 
t RCA Manufacturing Co., Inc., Los Angeles, Calif. 



Assuming that emf. generated by each ribbon is adjusted to be the 

same for zero degree incidence (6 = 0), then E P = E v 

= Eo (1 + cos 8) 

E 0) and 


The directional characteristic of the unidirectional microphone as 
expressed by eq. 2 is a cardiod of revolution, with the axis of revolu- 
tion normal to the plane of the ribbon. This characteristic is shown 
in Fig. 1 for the two-dimensional case. 

FIG. 1. Directional characteristic of 
unidirectional microphone. 

Four definite advantages for sound recording are expressed by such 
a directional characteristic. 

The fact that the sound striking the microphone from the rear is 
greatly attenuated prevents recording such undesirable sounds as 
camera noise, back-stage reflections, and what incidental noises might 
occur from that direction during a recording. 

The large solid angle of reception over which the microphone re- 
ceives sound without appreciable attenuation indicates that practically 
any action can be covered with a single microphone. This, of course, 
eliminates what interference is produced by the microphones when 
two or more units are used in covering an action, since the identical 
results are produced when the voltages from the microphones are out 


of phase as when sound-waves unite to produce near or complete 
cancellation of the vibrations in space. Much smoother dialog may 
therefore be expected with the use of one unidirectional microphone 
in place of two or more microphones of different types. 

The energy response of the unidirectional microphone to sound 
originating in random directions is one-third that of a nondirectional 
microphone. This means that for the same allowable reverberation, 
the unidirectional microphone can be used at 1.7 times the distance 
of a nondirectional mirophone. 1 No loss in intelligibility occurs when 
this greater distance is used, since the per cent syllable articulation 
of recorded sound is dependent only upon the amount of recorded 
reverberation* in a room free from noise and echoes. 2 

The directional characteristic of the unidirectional microphone is 
independent of frequency within all practicable reception angles. One 
of the most objectionable qualities of a pressure-operated microphone 
used in recording sound is the directional response that such a trans- 
mitter may exhibit for frequencies above 2000 cycles. While the 
polar response-frequency characteristic of an ideal pressure-operated 
microphone is a circle, as far as a plane through the transducer is con- 
cerned, in practice the response at the higher frequencies becomes 
noticeably attenuated for angles larger than 30 degrees on either side 
of the normal, or zero degree, incidence axis through the microphone. 
While such undesirable effects can be reduced by recording all dialog 
at some angle off the normal, such practice is greatly dependent on 
the experience and skill of the man who is entrusted with the handling 
of the transmitter during a recording. Considering, moreover, the 
manifold situations of a recording, the several sources of sound that 
either simultaneously or in quick succession must be recorded with a 
minimum of delay and hazard, it stands to reason that a microphone 
having a directional response independent of frequency will greatly 
reduce these objectionable abrupt loudness and quality variations. 

It may be stated at this point that a pressure-operated micro- 
phone, such as used in practice, tends toward a ratio of direct to re- 
flected sound in the recording that is larger for the high frequencies 
than for the low ones, if the microphone is used "beam on," because 
reflected high frequencies striking the microphone at large angles of 
incidence are attenuated by the microphone. While this has a ten- 

* Recorded reverberation is defined as the ratio of generally reflected to direct 
sound energy. 


dency to lend greater "presence" to the sound recorded b'y a pressure- 
operated microphone, the increased amount of low frequencies re- 
corded may exert a masking effect on this sound. Only experience 
will be able to state how important these two factors are, whether 
they neutralize each other, or whether the absence of one of them in 
the unidirectional microphone will be noticed in recordings made with 
such a microphone. 

In the following it is intended to describe a number of scenes that 
lend themselves particularly well to the use of a unidirectional micro- 
phone. These scones are specific, but by no means infrequent, and 
certainly have variations that can be covered equally well. 

Screening of Undesirable Sounds. Fig. 2 shows a subway tunnel 
the "ceiling" of which consists of iron grids opening to the sidewalk 
of the street above. It is intended to record only the dialog of the two 
persons in the tunnel, but not the footfalls of the passers-by above. 
The camera, on the other hand, is to photograph the entire scene, the 
actors speaking as well the actors overhead. A unidirectional micro- 
phone, skillfully concealed in the grating and oriented with the "dead 
plane" toward the sidewalk, represents an ideal solution for this 
difficult scene, since footfalls may later be "dubbed in" to an extent 
that will not mar the dialog but yet permit the auditor in the theater 
to hear actual, if faint, footsteps. 

Fig. 3 shows the hull of a ship in which two actors, at some dis- 
tance from one end, are talking. The hull, which is that of a real 
boat, is very "live," and considerable reflected sound comes from the 
end being photographed. A unidirectional microphone so oriented 
that its zero-degree incidence axis points toward the camera, will 
eliminate much of the undesirable reflected sound from the pictured 

Fig. 4 shows an actor being photographed near a tree and a water- 
fall, where the rush of the water is to be "dubbed in" in re-recording. 
A unidirectional microphone so placed that the 180-degree axis is 
directed toward the waterfall will reduce the sound of the water by 
approximately 20 db., which represents the difference in response be- 
tween the front and the rear of the unidirectional microphone. 

Use of Greater Microphone Distance. Fig. 5 represents a medium 
shot. Good recording practice calls for an "acoustic perspective" con- 
forming to the visual perspective of the picture seen on the screen. 3 
This means that, if a microphone may be said to have "focal length," 
its value should be equivalent to the optical focal length of the camera 







fctic,aoq panes 

386 J. P. LIVADARY AND M. RETTINGER [j. s. M. P. E. 

lens in order to achieve effective visual and aural coordination. In 
practice, however, it is not only difficult in many cases to position the 
microphone so as not to be within the camera angle, but cameras are 
often equipped with lenses of greater focal length, which calls for an 
even shorter distance between the speaker and the microphone than 
between the speaker and the camera. If a pressure microphone is 
placed barely outside the camera angle when such a condition exists, 
the auditor in the theater may gain the impression that the source 
of sound is not on the screen but behind it. A unidirectional micro- 
phone, however, having similarly a large "acoustic focal length," 
when placed at the position of the pressure microphone will create the 
effect of a pressure microphone situated at a distance six-tenths of 
that between the speaker and the unidirectional microphone. Indeed, 
with some care a position can be chosen for the unidirectional micro- 
phone that will not only maintain a high degree of intelligibility in the 
recorded sound when the transmitter is placed outside the view of the 
camera, but also the "acoustic perspective" can be made fully com- 
mensurate with the depth of the image on the screen a condition 
often referred to as "screen presence." 

Directional Response Independent of Frequency. Fig. 6 shows two 
actors engaging in rapid diaglog. If a "boom man" were to attempt 
to orient a pressure microphone so that its zero-degree incidence axis 
would point to each of the actors whenever he was speaking, several 
"takes" would probably be required to insure good intelligibility in 
the reproduced sound, if it can be had at all. On the other hand, if 
the pressure microphone remains stationary, with the zero-degree 
incidence axis pointing midway between the speakers, a type of 
recording can result that is sorely lacking at the high frequencies 
because of the narrow directional characteristic that so many pressure- 
operated transmitters exhibit.. This deficiency in high frequencies 
can, of course, later be remedied during re-recording by high-frequency 
equalization in the dubbing channel. Such post-equalization is, of 
course, necessary only when parts of the picture are recorded with 
the zero-degree incidence axis pointing directly at a speaker. If all 
dialog is recorded at a certain angle off this zero axis, only the amount 
of pre-equalization is used in the recording channel that will result 
in maximum intelligibility and naturalness of speech. Oversight on 
the part of a boom man, however, as well as almost unavoidable 
speaker configurations, tending to produce "beam-on" recording, 
make such a microphone difficult to manipulate, particularly when a 



crew is pressed for time. A unidirectional microphone, however, even 
as a velocity microphone, preserves the balance between the high and 
low frequencies in a recording up to very large angles of reception. 

Large Solid Angle of Reception. The use of two or more micro- 
phones to cover a large scene has several disadvantages. The level 
from the different microphones must at all times be balanced properly 
by the mixer, who is already called upon to control the overall gain to 
the amplifiers. Two or more men may be necessary to manipulate 
the microphones, causing additional difficulties in maintaining a 

FIG. 11. 

Arrangement of microphone and symphony 

D, Director 
M, Microphone 

B, 4 Bassoons 

C, 4 Clarinets 
F, 4 Flutes 
H lt 2 Harps 

H 2 , 8 French Horns 
Ob, 3 Oboes 
Ti, 3 Trumpets 

TZ, 2 Tympani and Traps 

7^3, 4 Trombones 

T 4 , 1 Tuba 

Vi, 12 First Violins 

V 2 , 10 Second Violins 

V 3 , 8 Violas 

F 4 , 6 'Cellos 

V 6 , 4 String Bass 

Total: 75 Musicians 

constant orientation of the microphones if they are of the pressure- 
operated type. Interference effects caused by the voltages from the 
the microphones being out of phase because of the spatial separation 
of the transmitters, may produce a blurred or "bumpy" recording 
not always readily detected by the mixer. Fig. 7 shows how a row 
of soldiers can be covered well by a single unidirectional microphone; 
for the sake of illustration there is also indicated the directional re- 
sponse of two pressure-operated microphones so placed to give similar 
coverage. Fig. 8 is a similar application of the unidirectional micro- 
phone covering a large garden party near a house by a noisy street. 



In the ordinary motion picture set consisting of a floor and three 
walls, the main part of the reflected sound which adds to the illusion 
of an interior setting is that reflected from the set walls. Reflections 
from the absorbent walls of the sound-stage are either too weak or, 
if noticeable, are usually delayed too long in time to contribute 
pleasingly toward such an illusion. Hence, if the atmosphere of an 
interior setting is to be preserved within its proper limits, it becomes 
necessary to collect as much as possible these reflections from the set 
walls before they strike the walls of the sound-stage. In this matter 
also a unidirectional microphone with its wide pick-up angle is an 

effective device toward the more 
realistic representation of the 
picture shown on the screen. 

Finally, when recording music, 
a satisfactory balance can often 
be achieved by the use of one 
unidirectional microphone and a 
judicious placement of the in- 
strument. Fig. 9 shows the re- 
cording of a soloist accompanied 
by a piano. The distance be- 
tween the vocalist and the micro- 
phone should be determined by 
the strength of his or her voice, 
and the piano should be placed 
accordingly for proper balance. 
Fig. 10 shows a set-up for record- 
ing a small band, such as a dance 
orchestra. The diagram is self-explanatory, the only precaution 
necessary being to keep the soloist at least two feet, and preferably 
three, from the microphone. Fig. 11 shows microphone and orches- 
tra arrangement for a symphony orchestra. 

There are also situations, however, that lend themselves less 
successfully to the use of a unidirectional microphone. Such scenes 
usually involve several actors, all of whom are speaking, while it is 
intended to record very clearly the voice of only one. Obviously, in- 
stead of using a microphone having a wide pick-up angle, a transmitter 
with a narrow solid cone of reception should be used. Likewise, when 
for some reason or other very close talking is necessary it is advisable 
to use a microphone that will not cause an increase in the low-fre- 

FIG. 12. Decibels correction as a 
function of frequency and distance of 
new type unidirectional microphone 
from a point source of sound (add 
correction to plane wave calibration of 


quency response when the distance between the speaker and the 
microphone is decreased. This low-frequency build-up is by no 
means so pronounced in a unidirectional microphone, however, as it 
is in a velocity microphone. Fig. 12 shows the variation of low-fre- 
quency response of a unidirectional microphone with variation in 
microphone distance. 

This variation in low-frequency response with angle of incidence 
may be calculated as follows : Let 

E p = Voltage output on a nondirectional microphone. 

C p = Sensitivity constant of this nondirectional microphone. 

E v Voltage output of a bidirectional microphone. 

C v = Sensivity constant of this bidirectional microphone. 

d = Microphone distance. 

F = Frequency. 

w = 2irF. 

A = Wavelength. 

t = Time. 

6 = Angle between the direction of the incident sound and the normal 
to the ribbon. 

then E p = C sin wt 

If C p = C v (unidirectional microphone having cardiod directional 
frequency response), then the output of the unidirectional micro- 
phone compared to that of a nondirectional microphone is given by: 

If = (normal incidence), this reduces to: 

Qi = Jl + - 006 
\ d 2 

or, expressed in decibels: 


1 OLSEN, H. F., AND MASSA, F.: "Applied Acoustics," P. Blakiston's Sons Co., 
Inc. (Philadelphia), 1934, p. 141. 

2 RETTiNGER, M. : "Note on the Velocity Microphone," J. Soc. Mot. Pict. 
Eng. XXIX (Dec., 1937), p. 629. 

8 MAXFIELD, J. P.: "Some Physical Factors Affecting the Illusion in Sound 
Motion Pictures," J. Soc. Mot. Pict. Eng., XVII (July, 1931). p. 69. 


S. K. WOLF** 

Summary. In the recording, acoustical, and electrical transmission of sound, the 
control of reverberation for purposes of speech articulation, musical quality, and 
acoustic illusion has been one of the problems confronting architects, broadcasting, 
recording, and acoustic engineers for some time. The paper discusses briefly the 
phenomenon of reverberation, and describes two methods of reverberation control: (1} 
reverberation chambers and (2) a practical machine employing magnetic recording. 

High-quality recording and reproducing require a wider and more 
accurate control of all acoustic characteristics, particularly reverbera- 
tion, in the never-ending quest for perfect illusion in sound motion 
pictures and radio broadcasting. Reverberation chambers for add- 
ing a fixed amount of reverberation to a sound recording or to a 
broadcast are already being used by the leading recording and broad- 
casting studios. These reverberation chambers introduce an addi- 
tional liveness into the sound that is not present in the studio where 
the original sound is being picked up. 

Such a reverberation chamber is normally a sizable room, approxi- 
mately 10,000 cubic feet, with walls of a glazed hard-surface material, 
and having a reverberation time of several seconds. In the reverbera- 
tion chamber are placed a loud speaker and a microphone. The loud 
speaker in the chamber is connected by suitable means to the micro- 
phone in the studio, and the microphone in the reverberation chamber 
is electrically connected to the sound-transmission channel. The 
output of this channel is then recorded or broadcast. In this way the 
acoustic liveness of the reverberation chamber will be added to the 
original sound picked up by the studio microphone Such a rever- 
beration chamber offers only a fixed amount of reverberation and is 
not capable of instantaneous variation or control. 

The acoustic control of sound recording or broadcasting either 
through reverberation chambers or in the space where the 

*Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 24, 
**Acoustic Consultants, Inc., New York, N. Y. 







original sound is created, depends upon the acoustic properties of the 
enclosure and the placement of the microphone relative to the sound- 
source. A correlation between microphone placement and acoustic 
characteristics of interiors has been worked out by Albersheim and 
Maxfield. If a sound is produced in a room, a short time elapses 
before the intensity of the sound reaches a maximum value. This 
time is called the growth time. If the sound-source suddenly ceases 
to emit energy, time elapses be- 
fore the energy is completely 
absorbed or falls below the 
threshold of audibility. The re- 
verberation time is defined as 
the time required for the sound 
to diminish to one-millionth of 
its maximum value. 

In Fig. 1 (A) is diagram- 
matically shown how the sound- 
energy in a room builds up to 
the stationary value and how it 
decreases to the threshold of 
audibility. The subjective im- 
pression upon the ear, which is 

logarithmic, is shown in Fig. 1 (B). 





FIG. 1. Diagram illustrating growth 
and decay of sound in a room. 

The growth time of the sound is 
scarcely detected (curve B) be- 
cause subjectively the sound 

seems to reach its peak value almost instantaneously, whereas the 
decay is more noticeable since it drops from a higher to a lower in- 
tensity proportionately with time. 

Experience has shown that music and speech require different re- 
verberation times and that different musical compositions require 
different rates of decay. Since it is always rather difficult to change 
the acoustic characteristic of a room at will there has been for many 
years a need for a practical method of artificially controlling rever- 
beration for producing any desired rate of decay of the sound. Since 
the growth of the sound is scarcely discernible, such a reverberation 
machine need only control the decay rate. However, the growth of 
the sound may be artificially produced, if desired for any reason, by 
the same method. 

The problem of artificial reverberation can also be expressed a little 



[J. S. M. P. E. 

differently. If, by some artificial means, the intensity of a sound can 
be controlled or regulated so as to correspond to the natural change of 
intensity, the effect must be the same as the effect of natural rever- 

A simple way of producing reverberation artificially is to record the 
sound and to have a number of time-displaced pick-up heads feed the 
energy, through adjustable volume controls, back into the trans- 
mission line to which the microphone is connected, through an 
amplifier of the desired gain and frequency characteristics. 

The volume controls are so adjusted that the amounts of energy 
supplied to the transmission line, from one pick-up to the next, follows 
an exponential law. To approach theoretically the natural rate of 

FIG. 2. Circuit diagram of reverberation unit. 

decay, an infinite number of pick-up heads would be required. For 
most practical purposes, however, several reproducing heads are 

An artificial reverberation machine must meet the following re- 
quirements : 

(1) Immediate playback. 

(2) Low maintenance cost. 

(3) Control of intensity and frequency response. 

(4) Mechanically and electrically fool-proof. 

Existing methods of sound recording can not fulfill these require- 
ments. Film recording used in the sound motion picture industry 
requires processing before reproducing. Mechanical recording is too 
expensive because of the necessity of continuously using new record- 
ing material. There are other methods of recording that are a prac- 



tical solution of the problem. One of the methods makes use of a 
tape coated with fluorescent material, which, when exposed to ultra- 
violet light controlled by a suitable light- valve, will fluoresce for a 
short while. This tape passes 
a number of photocells, which 
then pick up the sound and re- 
produce it. The exponential 
decay of the fluorescence has at- 
tracted experimenters to this 
means of creating artificial rever- 
beration. After a certain time 
the emission ceases, particularly 
if the exposure was made to 
infrared light, and a new re- 
cording can take its place. In 
this method the background- 
noise remains constant as the 
signal-level diminishes; the sig- 
nal-to-noise ratio therefore de- 
creases. For long periods of 
reverberation the fluorescence 
decays too rapidly. 

The author's method makes 
use of the principle of magnetic 
recording that has proved prac- 
ticable. A magnetic record may 
be instantly reproduced and im- 
mediately obliterated. A com- 
plete description of the principle 
of magnetic recording has been 
published in the JOURNAL by 
S. J. Begun. 1 For artificial re- 
verberation the tape may be 
used as shown in Fig. 2. The 
recording head a is supplied 
with energy from the microphone b and amplifier c. The pick-up 
heads (d, e, f, and g) and the recording amplifier are connected to a 
mixer amplifier, the output of which can either feed into a trans- 
mission line or a loud speaker. The mixer amplifier is provided 
with adjustable filters for the pick-up heads to make it possible to 

FIG. 3. 

Mechanism for driving 
the tape. 



[J. S. M. P. E. 

get any frequency-response desired in reproduction. Such adjust- 
ment of response is valuable since the reverberation time is not 
the same for all frequencies, and depends upon the absorption coeffi- 
cient of the room for different frequencies. It is very important 
that the sound-carrier move without appreciable variation of speed, 
particularly since the machine is used most frequently for musical 
reproductions. Fig. 3 shows a mechanism for driving the tape. A 
motor drives, through a belt, one cylinder a, and additional 

cylinders b are driven by 
the endless tape loop c, the 
ends of which are joined over 
two cross-over rollers d. This 
endless loop can be made 
long enough for any desired 
reverberation time, and as 
many reproducing heads can 
be arranged as required. The 
machine is normally provided 
with eight reproducing heads 
logarithmically displaced in 
time; the first so located that 
it will pick up the record af- 
ter 0.1 second, the second 
after 0.16 second, the third af- 
ter 0.25 second, the fourth 
after 0.4, the fifth after 0.66, 
the sixth after 1 second, the 
seventh after 1.7 seconds, 
the eighth after 2.7 seconds. 
The arrangement of the com- 
plete unit for motion picture studio and broadcasting use is shown in 
Fig. 4. The equipment is rack mounted, enclosed in a cabinet, and 
supported on casters so that it can be easily moved from one studio 
to another. 

Magnetic recording meets the quality requirements for synthetic 
reverberation : Its frequency responses, using adequate equalizers, are 
flat from 50 to 7500 cycles, and, if desirable, even higher. The 
signal-level is 40 db. above the background-noise. A sound-carrier of 
steel tape 0.1200 mil wide and 0.003 mil thick is used. This steel tape 
is particularly strong, and tests have shown its mechanical strength 








I [S] @ 

Pil/6S Si' 

Swee PAUCL as" 


VowHcCo/anoi OF PICK UP Hc*as\- 








FIG. 4. Arrangement of reverberation 
control unit. 


and electromagnetic properties to be entirely satisfactory. The ma- 
chine requires little servicing and is simple to operate. The mecha- 
nism shown in Fig. 3 has been designed jointly by S. J. Begun, 
A. Stapler, and the author. The electrical and physical designs of the 
unit have been anticipated by A. N. Goldsmith 2 in his patent on syn- 
thetic reverberation under which this company is licensed. 


1 BEGGUN, S. J. : "Recent Developments in Magnetic Sound Recording," 
J. Soc. Mot. Pict. Eng., XXVIII (May, 1937), p. 464. 

2 GOLDSMITH, A. N. : U. S. Pat. 2,105,318. 


DR. GOLDSMITH : The method here described is obviously one of which we shall 
hear more as time goes on, because it is impossible that reverberation of all sorts 
and types will be produced merely by simulating the actual physical chamber or 
enclosure in which the original reverberation might take place. It is manifestly 
not economical in the long run to have a great number of empty rooms or pipe 
lines of different characteristics not flexibly controllable, when such an ingenious 
mechanism as Mr. Wolf has described can be conveniently and economically used 
for the purpose. 

The versatility of that type of mechanism depends upon the work in connection 
with magnetic recording that was described. The problem of producing a reliable 
telegraphone is not so simple as it sounds, because if one takes a piece of steel 
wire and tries to run it around in a loop over and over again, he soon makes the 
interesting discovery that steel can be defined as a material that kinks and snaps 
itself automatically. The problem of producing telegraphones with wire elements 
is difficult if one requires reliable, continued operation, and it takes a clever ar- 
rangement, such as this steel-tape holder, to accomplish the results in heavy-duty 

The flexibility of the circuits and arrangements that have been shown is perhaps 
greater than has been indicated. Thus, if one wants to simulate the acoustics of 
a room which has walls, floor, and ceiling of different characteristics, one can 
divide the reproducing pick-up heads into three major groups corresponding 
respectively to the horizontal right and left walls, the front and back walls, and 
the ceiling and floor, and then put into the circuits of the reproducing heads cor- 
rective networks corresponding in general to the frequency and also the phase-of- 
reflection characteristics of the walls in question; so that one can modify each of 
the three groups of major reflections more or less systematically as desired. 

Other interesting possibilities exist. In the panel arrangement that was shown 
are a group of reproducer amplitude controls that is, volume controls. It is 
possible to interconnect those by chains, levers, or other mechanical means, so as 
to have a master control. One can even move the recording heads along, changing 
the time of each delay ; or vary their amplitude systematically, or both, so that by 
means of a simple knob one can go to extremes of flexible control, one can change 

396 S. K. WOLF [j. s. M. p. E. 

the delays in each reproducer head relative to fundamental sounds and change the 
relative amplitudes and/or tone qualities from each. So one could conceivably 
have a knob with a pointer moving over a scale marked: "small room of wood," 
"larger room of stone," "scene under a bridge," "cathedral interior," and so on; 
and by merely turning the knob one could actually change the resulting acoustics 
over this wide series of conditions. 

There are other interesting applications, as Mr. Wolf has pointed out, for this 
technic ; but one of the main points that should be considered is that the acoustic 
output-to-ground-noise ratio of each of the echoes produced by the machine re- 
mains satisfactory. 

There is another point of interest. It is believed telegraphone recording equip- 
ment is entirely adequate for the purpose mentioned, for two reasons, first, be- 
cause its tonal quality is very high when it is properly built ; and, second, because 
the role played by the very high frequencies is less in synthetic reverberation than 
in the original sound. 

Finally, there is another point of interest. To the practical man carrying out 
recording in studios, this device offers the possibility of later sound editing on a 
large scale, because he can take an original record of sound in "dead" surround- 
ings, and then he can add any desired type of reverberation at any time thereafter. 
This he can re-record in any desired fashion as often as desired, and experiment 
and produce different types of reverberation until he finally hits the one that 
gives him, for example, the effect of a man walking out of a room into a tunnel and 
into a larger room. That can be experimented with over and over again until 
the desired result is obtained, without injury to the original record. 

Perhaps I should apologize for the length of this discussion, but I am greatly 
interested in the whole philosophy of producing sound effects by electrical means 
rather than by clumsy, large, and costly, mechanical means. 

MR. KELLOGG : My first SMPE paper was read in 1928 under the title, "Some 
New Aspects of Reverberation," in which I indulged in the speculation that since 
we did not need reverberation to help intensity any more with our electrical appa- 
ratus, we could control things beautifully if we could only get rid of the natural 
reverberation and supply just what we wanted where we wanted it and when we 
wanted it by various electrical devices. It seemed that the remarkable flexi- 
bility and power our new electronic and acoustic tools were going to give us better 
control than we have ever had before. 

Well, I have been waiting during the intervening ten years to see any of that 
really done. After all, I do not think that such mere speculation as I indulged in 
is a particular credit compared to really doing something about it. 

There is one aspect in the production of reverberation by a recording sound 
system which is not necessarily an indication of its being faulty, but it is funda- 
mentally different from what we will get with any normal natural reverberation. 
If the absorbent qualities of the walls are such as to cause, let us say, twice as much 
absorption at 5000 cycles as we have at 2000, the 2000-cycle tone would be audible 
for twice as long a time as the 5000-cycle tone. In the case of reverberation pro- 
duced by recording the sound, if the rate of attenuation is determined by the gain 
settings of the several pick-ups, all the components will have the same reverbera- 
tion time. Therefore, the only kind of room this will truly simulate is one which 
has exactly equal attenuation at all frequencies. 


I am not saying that the kind of reverberation you may get by the recording 
method may not be even better, provided you keep the ground noises down, but it 
is essentially different. 

There is one phase of the question that I feel deserves much consideration. 
It seems to me to be very desirable, if we have a ready means of producing arti- 
ficial reverberation, to do it in the listening and not in the recording. I grant that 
by doing it in the recording you make it available for all theaters, but the ideal 
system which I hope ultimately to see in use is one in which the original sound 
recorded with very little reverberation, and in the reproduction the non-reverber- 
ant sound will come from a speaker directly in front of you, and echoes will come 
from speakers scattered around the room. 

We tried some experiments a number of years ago in Camden to check out this 
idea, and it works according to theory very nicely. If we put all the echoes 
through one loud speaker in front of us we got the impression of sound coming 
down a long hallway. Although the tests were made in a small room we got quite a 
good illusion of being in a large room when we produced only the initial sound 
under a loud speaker directly in front, and the reverberation or echoes with scat- 
tered speakers around the room. 

We did those experiments with a record and a series of pick-ups. The thing one 
would naturally be likely to do in arranging a series of pick-ups would be to space 
them uniformly. We did not get far enough to make any analysis of that, or to 
try many variations, but such uniform steps are obviously not what happens in 
the echoes we get in natural reverberation. Can Mr. Wolf tell us what he has 
found in the way of optimum arrangements? 

MR. WOLF : I did not quite follow some of your reasoning as to why we could 
not simulate the reverberation condition. Theoretically, with the flexibility that 
we have, we believe that we can simulate or at least create the illusion of any de- 
sired reverberation condition. 

The distribution of the reproducing heads is not very critical. We are now 
building a machine on which we can put as many as 40 or 50 heads, or even more 
if desirable. Preliminary experiments indicate that only a small number of heads 
are necessary and their positions are not very critical. They may be spaced 
logarithmically or uniformly, and still produce a very good illusion of reverbera- 
tion with a small number of heads spaced almost at random. 

DR. GOLDSMITH: There is another point of interest in this connection. It is 
possible, of course, to simulate effects in a room having different attenuation rates 
for the different frequencies by placing in each reproducer -head circuit a fre- 
quency-selective circuit, so that with the passage of time one cuts down the 
different frequencies to different extents. It is thus possible to simulate the de- 
sired effect. 

MR. KELLOGG: I checked that, by increasing attenuation of certain fre- 
quencies on the pick-ups that are reached successively by the location. 



Summary. From the earliest days of artificial lighting the broadside type of 
unit has been a fundamental lighting tool. Regardless of the light-source used in such 
lamps whether mercury-vapor tubes, carbon arcs, or incandescent filament globes 
the broadside is a lamp of the floodlight type, designed to emit a relatively wide flood 
of soft, moderately powerful illumination. It has withstood innumerable changes in 
lighting and photographic technic, including the introduction and acceptance of spot- 
lighting, the change from orthochromatic to panchromatic film, the changes from silent 
to talking pictures and from arc to incandescent light-sources, and the present growing 
popularity of natural-color photography. 

The paper traces the evolution of arc broadsides only, and comment upon the design 
and performance of the early units. The evolution of the broadside is followed through 
successive improvements in silent-picture usage; its decline at the introduction of 
sound and Mazda lighting; through the relatively recent rebirth of arc lighting due to 
the requirements of modern natural-color photography; and the most recently intro- 
duced units of this type which are replacing equipment designed less than five years 
ago at the introduction of the three-color Technicolor process. Comparison is made 
between the early, intermediate, and modern units as regards color distribution, 
light distribution, steadiness and length of burning period, indicating that though 
less public attention has been given to these types than to the more familiar spot- 
lighting units, the broadside has kept pace with advances in lighting and equipment 

The first artificial light-sources used to illuminate motion pictures 
were of the "broadside" or floodlighting type. From that day down 
to this, the "broadside," regardless of the type of light-source it housed, 
has remained a fundamental tool of motion picture lighting. 

So far as is known, the first installation of artificial lighting for 
motion picture production was made at the original Biograph studio 
on 14th Street, New York, N. Y., in 1905. The lamps used were 
primitive "banks" of mercury- vapor tubes, suspended above the sets 
under the glass roof, to supplement to daylight on dull days, and to 
replace it on dark ones. 

Other pioneer producers and technicians were not long in appreci- 

* Presented at the 1938 Fall Meeting at Detroit, Mich. ; received October 31, 

** Mole-Richardson, Inc., Hollywood, Calif. 


ating the commercial advantages of artificial lighting, and in time 
virtually all the eastern studios equipped themselves with mercury- 
vapor lighting equipment. When the industry began its migration 
to California, the vapor-tubes followed, for in spite of the most en- 
thusiastic claims, clouds do sometimes obscure the California sun, and 
artificial lighting remained a commercial asset. 

As this development progressed, the mercury- vapor tubes were 
adapted to a variety of units, all of the floodlighting type. In addition 
to the original overhead units were "broadside" units of from six to 
eight tubes, mounted on wheeled stands to permit their use on the 
stage floor; "goose-neck" units which resembled the "broadside" 
banks but with the addition of a second bank, mounted above the 
first and directed at a downward angle ; and in some instances special 
low front-lighting units (usually of four tubes) mounted horizontally 
on a low, wheeled carriage and used to throw light upward against 
the faces of the players. 

The first arc-light unit to appear seems to have been the Aristo, 
introduced not long after the introduction of the vapor tube. This 
unit, which was an adaptation of similar street-lighting units, was an 
overhead floodlight. It was a single arc, burning at about 28 amperes 
and 63 arc volts. It was commonly fitted with a simple conical 
reflector reminiscent of those on street lamps, and the arc was en- 
closed in a glass globe. With its small dimensions and relatively high 
power for those days, it became very popular for supplementing na- 
tural light on glass stages. 

The introduction of true arc "broadsides" that is, floodlighting 
units for floor use appears to have taken place about 1912. Ac- 
cording to cinematographers active at the time, the Wohl was one of 
the first, if not actually the first of these units used. It, like most of 
its successors for a decade or more, was an adaptation of units pre- 
viously made for photoengraving. These pioneer lamps were what 
might be called double-twin arcs, for they consisted of a pair of twin- 
arc units, each with a large, box-like reflector, mounted one above the 
other on a common stand. The stand consisted of three upright posts, 
arranged parallel to each other in a triangular formation; the lamps 
slid up and down between the two front posts, while a counterweight 
operated on the third post. The four arcs were wired in series-multi- 
ple. They burned at 30 amperes when all four arcs were connected 
in series across a 220-volt circuit, or at 60 amperes if each two arcs 
were burned independently in multiple on a 110-volt line. 

400 P. MOLE [j. s. M. P. E. 

The advantages of arc lighting became increasing pronounced as 
cinematographers drew away from the earliest flat lightings and be- 
gan to experiment with the possibilities of creating effects of contour 
and separation of planes by contrasts in lighting. A considerable 
variety of arc "broadsides" were built during the next several years 
by a number of manufacturers. Among these might be mentioned 
one curious design in which a single arc of relatively high power (30- 
40 amperes) was mounted to burn horizontally in a semicylindrical 
reflector, and another in which the carbons were placed at right angles 
to each other. In general, however, the successful designs soon 
evolved to the form familiar to all who have had any experience with 
production prior to the early days of sound. 

In general, these lamps were of the twin-arc type with the two arcs 
placed beside each other with the carbons vertical, and burning in 
series at about 30 amperes. The lamp was mounted on a pedestal 
quite similar to the types in general use today, with the necessary 
ballast resistance at the base of the pedestal. 

These arcs were generally used in conjunction with the softer vapor 
tubes. Before the introduction of arc spotlighting equipment, they 
were the only sources of strongly directional "hard" light available. 
In some studios the way in which the "hard" and "soft" lighting was 
mixed was left to the cameraman. In others, a rigid studio policy 
dictated the lighting: in some such cases all the vapor lights might 
be used overhead, and all arcs on the floor; in others, vapor lights ex- 
clusively on the floor, and arcs overhead. 

A common malady throughout all the days of the early arcs was 
the so-called "kleig eye," medically termed conjunctivitis. It was 
a painful inflammation of the eye and eyeball. The cause was 
simply ignorance of the spectral characteristics of arc lighting. Arc 
light has always radiated strongly in the injurious, short-wave ultra- 
violet region. At that time, the lamps were very generally used with 
no diffusion, or at best a simple scrim of silk or tracing-cloth which, 
of course, failed to impede the ultraviolet rays. Since the rebirth of 
arc lighting five or six years ago, modern knowledge of spectral radia- 
tion has virtually eliminated this malady. Ordinary lead glass ab- 
sorbs all the injurious components of the ultraviolet radiation. Ac- 
cordingly modern arcs are always used with some sort of a lead-glass 
window clear, if no diffusion is wanted; translucent, if diffusion is 
desired. And "kleig eye" is known only to press agents seeking imagi- 
nary copy. 


The performance of the early arcs left much to be desired. Of 
course, when motion pictures were the silent drama, it did not mat- 
ter whether or not lighting equipment burned silently; but then, as 
now, a steady-burning light-source was important to good cinema- 
tography. Even the most enthusiastic booster of these early lamps 
could not deny that they flickered badly, and frequently went out at 
the most inopportune moments. It was probably fortunate that the 
film used in those days was of relatively limited sensitivity, for main- 
taining a mere exposure level of illumination usually required the use 
of so large a number of overlapping lamps that the effects of flickering 
by individual lamps were minimized. 

In a certain measure this performance was due to the then relatively 
limited knowledge of carbon design and production. Fundamentally, 
however, the flickery performance of all types of pre- talkie "broad- 
sides" must be laid to the crude methods of feeding the carbons. Some 
early lamps even used a simple, hand-operated gravity feed. The 
majority made use of some type of gravitational-magnetic feed, which 
fed both arcs simultaneously. The result, of course, was an exceed- 
ingly intermittent feed. The lamps would burn with less and less in- 
tensity and increasingly pronounced flicker as the arc -gap grew wider. 
Then the carbons would suddenly feed, after which the light would 
momentarily become abnormally brilliant, and then diminish slowly 
as before. The electricians of those days used to keep long poles 
available on the sets with which to beat or jolt the lamps at the start 
of each "take," in the hope that the jolt would cause the carbons to 
slip down and thus minimize flickering during the scene. Floor lamps 
were often shaken, and the main switch flipped rapidly on and off 
for the same reason. The percentage of otherwise good scenes 
spoiled by lamp flicker was high. 

Fig. 1 shows a curve made by one of these lamps with a General 
Electric recording photometer. The lamp used was a typical twin- 
arc "broadside" of the later, pre-Vitaphone vintage. It is possible 
that when the lamp left its maker's hands some fifteen years ago its 
performance might have been considerably more creditable; but time 
unfortunately did not permit completely reconditioning the unit, and 
the test was made with the lamp in approximately the condition it 
would be in under normal studio usage of its period. 

It will be observed that when first struck, the arc leaps to a rela- 
tively high intensity, reaching a peak after about 30 seconds, after 
which the intensity rapidly decreases, with frequent and strongly 



[J. S. M. P. E. 

noticeable fluctuations; until, after approximately 3 l / 2 minutes of 
burning, when the intensity has declined to approximately l /a its 
original value, the lamp retrims itself, without, however, regaining 
more than 2 /s of its initial intensity. Thereafter the cycle of decline 
and retrimming repeats itself. 

Similar tests, covering a period of an hour's burning, were even 
more noteworthy. The short-period fluctuations already noted stood 
out prominently, and superimposed upon them was a pattern of 
longer-period fluctuations of still greater intensity. These occurred 
at approximately 5-minute intervals, and at the peaks the recording 
stylus was thrown completely off the scale. Immediately before these 

f . ; '\ 


larly twia 
broads! <5s 

FIG. 1 . Characteristic of early type of lamp, prior to 1926. 

peaks, as the carbons in retrimming momentarily touched before 
striking what for all purposes was a new arc, the intensity dropped 
to zero. 

It will be seen that there was a triple flicker in these lamps, phased 
as follows : first, minor variations in intensity at intervals of less than 
2 seconds; second, fluctuations of 40 to 50 per cent at intervals of ap- 
proximately 3 minutes; third, fluctuations of several hundred per 
cent at approximately 5-minute intervals. Thus while these lamps 
would actually burn for considerable periods, it will be obvious that 
for true photographic effectiveness it was seldom safe to burn them 
continuously for more than 3 minutes, or at most 5 minutes without 
extinguishing for adjustment. Even during this short burning period, 
they were only momentarily at their best performance. 


The coming of sound and the introduction of panchromatic film, 
occurring a most simultaneously, spelled the doom of these early 
arcs. Even though it was in time found that arcs could be silenced 
quite effectively by the application of choke-coils, the much longer 
scenes general in talking pictures demanded the use of steady, flicker- 
free illuminants. At the same time, panchromatic film's stronger 
sensitivity in the yellow-red region made the early arcs, which were 
deficient in this range, inferior to the steadier and redder incandes- 
cents. High-intensity arc spotlights, of course, continued in oc- 
casional use, since no other illuminant could compete with their 
strong, intensely directional beams for certain dramatic lighting 

The arc was reborn about five years ago, with the introduction of 
the three-color Technicolor process. With any process of natural- 
color photography or cinematography the color of the light is of 
fundamental importance, both technically and commercially. The 
color control possible in the camera's separating filters, and in the 
multiple color-printing operations naturally make a certain degree of 
compensation possible. Natural daylight, however, is a fairly uni- 
form blend of rays of all spectral colors. If the system is balanced 
for this standard, there is difficulty in using it with light which, like 
the incandescent, leans to the red end of the spectrum, or, like the 
earlier arcs, leans to the blue end. Printing color-control alone is 
seldom sufficient to compensate for such differences. The filter- 
balance of the camera can; of course, be altered to make such com- 
pensation. But this is not commercially feasible, for it would necessi- 
tate either readjusting the camera-filters, which are an integral part 
of its optical system, or the use of completely different cameras 
whenever a company went from an artificially lighted stage to na- 
turally lighted exteriors. A further complication is found in the gen- 
eral practice of using "booster" lights to supplement natural light 
outdoors. To be useful, such artificial light must mix imperceptibly 
with daylight. 

The logical requirement in lighting the one that the Technicolor 
engineers set up as a basic standard would be that the artificial 
light must have as nearly as possible the spectral distribution of nat- 
ural light at mid-day. 

Certain other requirements, almost equally important, also existed. 
The light-losses inevitable to distributing an image over three films, 
and absorbing color-components of each with selective filtering, 

404 P. MOLE [J. S. M. p. E. 

necessitated, especially at the outset, illuminants of high intensity. 
The requirements of talking pictures naturally presupposed a silent 
lamp, while the length of scenes in such pictures made flicker unde- 
sirable. The high sensitivity of the Technicolor process definitely 
called for flicker-free lamps. 

Arc lighting seemed inherently more nearly suited to these require- 
ments. Arcs are the most intense illuminants thus far available for 
motion picture lighting. Experience had shown how they could be 
silenced satisfactorily. Their radiation, while not then ideally 
matched to the daylight standard, even then seemed more nearly 
suitable and appeared capable of being made more so. On the other 
hand, the arcs then available, especially the fundamental "broadside" 
types, flickered badly. Since much scientific knowledge had been 
amassed since the design of these early lamps, however, it appeared 
hopeful that flickering could be overcome, or at least minimized. 
Accordingly the Technicolor Motion Picture Corporation commis- 
sioned the Mole-Richardson engineers to develop arc equipment 
suited to modern production in the three-color Technicolor process. 

Since the fundamental lighting tool was the "broadside" arc, and 
since the then-existing "broadsides" were perhaps the least adequate 
of any existing units, the first lamp to be developed for three-color 
Technicolor cinematography was the "Side Arc" (MR Type 29). 
This unit has been thoroughly described in previous papers, and 
little need be said in detail about it at this time. While similar in 
appearance to previous arc "broadsides, "'in design and performance 
it was revolutionary. 

This lamp, though it operated at 40 amperes, used carbons much 
smaller than any previously used in arc "broadsides," and of different 
composition. These carbons were specially developed for the pur- 
pose by the National Carbon Company, and were known as 8-mm. 
Motion Picture Studio Carbons. The light radiated was an almost 
perfect substitute for daylight. The intensity of the light of these 
lamps was approximately 250 per cent greater than that of previous 

Like previous arcs of the same type, the twin arcs were burned in 
series, with a ballast resistance. Instead of feeding simultaneously, 
as did most previous "broadsides," each pair of carbons was fed and 
controlled independently, to maintain the required voltage across 
its arc-gap. This naturally did much to eliminate flicker. 

Fig. 2 shows a record of a test made with one of these lamps. It 



will immediately be observed that the characteristic slow loss of inten- 
sity, and the longer-period fluctuations of the previous type arcs have 
been eliminated, although considerable minor variation still remains. 
However, judged by the "broadsides" then existing, and by the arc 
spotlights then used, the Side Arc was considered a flickerless lamp. 
For overhead use a companion design (MR Type 27) was made, 
mechanically the same, but mounted for overhead use. It was known 
as the "Scoop." 

During the ensuing five years new and greatly improved types of 
arc spotlighting equipment (MR Types 65, 90, and 170) have been 
brought out, as detailed in previous papers. Their performance was 

K8 Type 89 

FIG. 2. Characteristic of side arc. 

so improved that the imperfections of the Type 29 Side Arc became 

Two improvements in arc "broadsides" were deemed especially 
necessary: first, further reduction of flickering; second, longer burn- 
ing periods without retrimming or other attention. The latter was 
of definite commercial importance, for much time was lost retrimming 
large batteries of arcs, especially the overhead Scoops, on large sets. 

Those requirements have been met in a new unit, introduced only 
within the last two months. Known commercially as the "Duarc" 
(MR Type 40), it embodies principles not hitherto employed in 
studio floodlighting arc equipment. 

Research in connection with the design of high-intensity arc spot- 
lights had indicated that in these rotary-carbon spotlights much of 



[J. S. M. P. E. 

the flicker was eliminated by continuous feeding of the carbons. 
Therefore, in the Duarc the carbons are fed continuously. Each 
arc is, of course, fed and controlled individually. 

Front and rear views of the Duarc are shown in Fig. 3, while the 
same lamp, without its covering, is shown in Fig 4. It will be seen 
that each pair of carbons is fed by means of an endless chain; the 
carbon-holders are mounted on opposite sides of this loop in such a 
way that as one holder ascends the other descends. Each chain is 

FIG. 3. Front and rear views of the Duarc. 

driven by an independent, slow-speed electric motor, which requires 
only 600 revolutions to feed completely a trim of carbons. This re- 
quires over 2 hours. 

The operation of these motors, and hence of the carbon feed, is con- 
trolled automatically by the resistance across each respective arc. 
This is done by an adaptation of the familiar Wheatstone bridge 
principle of balanced resistances. 

The cycle of operation in the Duarc is as follows. When the master 
switch is thrown, current is fed into the motors, causing them to re- 
volve sufficiently to bring the carbon electrodes into contact. As the 
current flows through these electrodes, the motors immediately and 



automatically reverse themselves, drawing the carbons apart to form 
the arc. When the carbons are so separated as to give the most satis- 
factory arc, the motors again reverse and drop to the very slow speed 
of 5 rpm. ; then they feed the carbons continuously, at a rate in each 
case dictated by the resistance across the individual arc-gap, keeping 
the arc at its most favorable point until the carbons are consumed. 
Special 8-mm. positive and 7-mm. negative carbons have been de- 
veloped for this lamp by the National Carbon Company. 

FIG. 4. Front and rear of the Duarc, with covers removed. 

The practical result of these improvements is shown in Fig. 5. 
From this curve, made under conditions similar to those of the two 
previously shown for earlier types of "broadsides," it will be seen 
that while minor fluctuations still exist in the light-flux of the 
"Duarc," they average less than % the magnitude of those of the 
Type 29 Side Arc, and less than l /25 the magnitude of the pre-talkie 
"broadside." They are scarcely evident, either visually or photo- 
graphically. The several superimposed fluctuation patterns of greater 
magnitude and longer period, evident in the earlier lamps, have wholly 



[J. S. M. P. E. 

disappeared. For all practical purposes it may be said that the long- 
sought goal of an absolutely flickerless arc "broadside" has at last 
been attained. 

At this point may be mentioned one of the frequent instances where 
the performance concepts of the engineer and the practical comeraman 
do not agree. Measurements of the intensity of the light-flux radiated 
by the Duarc, made by Mole-Richardson and Technicolor engineers, 
indicate that there is very little difference between the intensities of 
the new Duarc and the older Type 29 Side Arc. This is as it should be, 

FIG. 5. Characteristic of the Duarc. 

for increased uniformity of light-flux, rather than increased intensity, 
was the aim from the start. 

Several cinematographers, on the other hand, after using the new 
lamp on production, have reported that they obtained better results 
with the new lamp, used 8 feet distant from the subject, than they 
did with the earlier Side Arc at half the distance. 

A number of practical improvements in design have been possible 
by virtue of the radically different principles involved in the new unit. 
For one thing, earlier ' 'broadsides" were generally fitted with a hinged 
cover over the upper part of the carbon-feed mechanism. This cover 
was almost invariably opened when the lamp was in use, for better 
ventilation. In the Duarc, asbestos insulation is applied behind the 
sheet-metal housing of the unit, and between the reflector and the 


mechanism. The latter, especially, insulates the mechanism from the 
heat of the burning carbon electrodes. More accurate knowledge of 
convection currents within such a lamp also dictated the design of 
ventilating ports and inner light-baffles. As a result, the operating 
mechanism of the Duarc is semipermanently sealed. In actual use 
there is no reason for opening this compartment save for rare major 
repairs which would, of course, never be made on the set. 

The only manual operating controls are the main switch and two 
knobs which project from the front of the lamp, directly below the 
reflector. Each of these is connected to one of the two carbon-feed 
chains. Their purpose is to permit quick separation of the upper 
and lower carbon-holders when the lamp is to be re trimmed. 

The carbon-holders are of the quick-release type, consisting of a 
split bushing compressed by a small coil-spring. The butt-ends of 
the carbons are simply inserted in these holders, after which the 
spring-loaded bushing holds them fast. No tools are needed for trim- 
ming or re trimming the lamp. 

Another innovation is found in the diffusing screen and its mount- 
ing. Previously, because of the heat radiated from the arc, such 
diffusers had necessarily to be made of relatively narrow strips of 
glass, mounted in a frame that, for better ventilation, was simply 
hung rather loosely over the front of the lamp. 

The diifuser used in the Duarc is constructed of a single sheet of 
translucent pyrex heat-resisting glass, mounted in a rigid cast- 
aluminum frame. This frame fits closely over the lamp opening. For 
trimming or inspection, the frame slides up and off a tongue-and- 
groove joint like a window-screen. Ventilation is cared for without 
the necessity of any opening between the lamp and the diffuser, while, 
of course, the use of pyrex virtually eliminates heat-breakage risks. 
The frame design prevents undesired "spilled light," including both 
visible and ultraviolet rays. The diffuser frame is hinged to open like 
a book, so that the diffusing screens may be replaced easily, while in 
the somewhat rare event that no diffusion is needed, a pane of clear 
pyrex may be used. Hooks are provided by which additional diffus- 
ing media, silks and the like, may be hung over the regular diffuser 
as desired by the cameraman. 

The Duarc is a twin-purpose unit. Ordinarily it is mounted on a 
conventional three-lift pedestal for floor use, allowing a wide range of 
adjustment from very low to very high positions. Alternatively, 
special chain hangers are available by which the same units may be 

410 P. MOLE [J. S. M. P. E. 

utilized either singly or in banks for suspended overhead units, re- 
placing the older "scoops" previously referred to. 

The fully automatic operation of the Duarc gives a very practical 
advantage for this latter use. Much time is ordinarily lost with 
"scoops" of conventional type when used on large sets, due to the 
relatively frequent need for re trimming. Such units are suspended 
from the roof-trusses of the stage, directly over the set. They are 
in most cases quite inaccessible. Re trimming means that the lamps 
must be lowered to the floor so that the electricians can get at them; 
in only rare instances it is possible to reach them by ladders. In any 
event, reaching and retrimming large batteries of such lamps is a 
serious interruption to shooting. In a modern production, where 
overhead costs may mount up at several hundred dollars an hour, 
such delays are not only inconvenient, but expensive. 

The Duarc, however, has an unusually long burning period, as it 
burns both carbons down to stubs less than three inches long. Under 
both tests and practical operating conditions, these lamps have burned 
without attention for periods in excess of 2 hours, on a single trim. 

In practice, this means that with only reasonable care to turn the 
lamps off during nonproductive periods between takes, the Duarcs, 
used as overhead lamps, may be used without retrimming for not 
less than half a day. Under some conditions, where production for 
other reasons is slow, the lamps may well operate for a full day on one 
trim. In any event, no shooting time need be lost, as the lamps can 
be retrimmed at the noonday halt, and need no other attention dur- 
ing the day. 

Since the lamps automatically strike their arcs whenever the cur- 
rent is switched on, they may be operated either singly or in banks 
by remote-control switches. An interesting fact revealed in recent 
tests of these lamps is that by the use of a conventional dimming 
rheostat it is possible to fade these lamps in and out with no ap- 
preciable flicker a valuable asset in certain types of dramatic effect- 
lightings. Since the Duarc strikes its arc almost noiselessly, and 
settles down immediately to steady burning with no initial period 
of abnormal strength, these lamps may also be switched on or off 
as required in the middle of a scene. 

It is evident that in the approximately 26 years since the introduc- 
tion of the industry's first arc "broadsides," the design, performance, 
and operation of these fundamental units have made genuine prog- 
ress. Yet during much of the period, "broadside" design remained 


actually almost static, as the more spectacular spotlighting units were 
introduced and developed. The original principles of "broadside" 
design, borrowed from other fields, had seemed good enough. Only 
when more scientific methods of design were applied, together with 
a willingness to cast aside previously conventional practices and de- 
velop lamps wholly intended for motion picture use, was radical 
progress made. The same has been true of spotlighting equipment 
as witness the advances made when previously conventional ideas 
were supplanted by the modern Fresnel-lens spotlight designs, ori- 
ginated solely for motion picture lighting and the same must be true 
of virtually every other phase of equipment design for motion picture 
apparatus. Having attained the status of a major scientific industry, 
the motion picture should no longer be satisfied to borrow and adapt, 
but can strike out for itself, designing and using equipment planned 
exclusively for the special requirements for making better motion 


DR. GOLDSMITH: How close can you bring a broadside like that to an actually 
recording microphone without the microphone picking up anything from the mo- 
tors during automatic feeding? 

MR. MOLE : We have placed this new lamp within six feet of the microphone 
and have found it very satisfactory. It depends entirely on the particular dra- 
matic effect that you are trying to accomplish in recording. 

A short time ago, in a picture in which Shirley Temple was the principal artist, 
these broadsides were used and we were confronted with a problem of recording the 
scene in a very low key. Nevertheless, we were able to use these lamps within 
about six feet of the microphone with satisfactory results. 

MR. FINN : What is used for the mat surface diffuser? 

MR. MOLE : The diffuser, which is placed in front of the lamp, is pebbled and 
sandblasted glass. It gives a soft, diffused light on the subject. The reflector is 

DR. GOLDSMITH: So you get your efficiency of reflection from the chromium- 
plated reflector and depend on the diffusers for the quality of the light, that is, the 
softness or diffusion? 

MR. MOLE: Yes. 

DR. GOLDSMITH: Have you ever tried to any extent successfully using a hard 
spot with a diffuser on it, when you have to place the lights quite a way off from a 
set, and yet desire controlled diffusion? 

MR. MOLE: Sometimes they use a 150-ampere Sun arc, with a diffusing glass in 
front of it, to give a large diffused surface. 



Summary. Some experiments on the toning of motion picture positive film by 
the methods of direct dye coupling color development, which have heretofore been applied 
principally to natural color processes, are described. 

Also methods of obtaining a wide range of colors and of controlling contrast are dis- 

During the past year there has been a revival of interest in the ton- 
ing of motion picture positive film. Several productions have ap- 
peared that were toned throughout and others in which certain se- 
quences were colored. The tendency in the application of these tones 
has been to obtain a subtle coloring of the image rather than the 
blatant results that in previous years were associated with toning 
processes. 1 In fact, the recent productions have used browns and 
blues to obtain blue-black or warm black tones rather than definite 
blues and browns. 

Essentially the process of toning motion picture film consists of 
converting the silver image to, or replacing it with, a colored com- 
pound. In this respect toning differs from tinting since only the 
image is colored, the highlights remaining clear. There are many 
methods available for obtaining these toned images but the majority 
fall into a few general classes. 

(1) Metallic Toning. (a) The conversion of the metallic silver to a colored 
silver compound. The common method of obtaining a sepia by sulfide toning is 
an example of this. 

(b) Replacement of the silver image with a colored metallic compound, fre- 
quently a ferrocyanide. Iron and uranium toning are the outstanding examples; 
iron producing the familiar blue ferriferrocyanide while uranium yields the reddish - 
brown uranium ferrocyanide. Recently, toning with uranium has been a more 
popular method of obtaining warm blacks than has the older sulfide method. 

* Presented at the 1938 Spring Meeting at Washington, D. C.; received 
May 26, 1938. 

** Agfa Ansco Corp., Binghamton, N. Y. 



(2} Dye Toning. (a) The conversion of the silver image to a salt that will 
mordant basic dyes. This method is well known and has been used for some time. 
The image is generally converted to either silver iodide or uranium ferrocyanide. 
Both these compounds have strong mordanting characteristics. The difficulty 
with this method has been to obtain an image in which the dye tone is not con- 
taminated with the color of the mordanting salt and, secondly, to obtain basic 
dyes with sufficient color range and stability. 

(5) Differential Hardening Methods. (a) The silver image is treated with a 
bleach and the products of the reaction between this bleach and the silver hardens 
the adjacent gelatin so that dyes will be differentially absorbed. This has had 
comparatively slight application to monochrome toning but has found some 
application in natural color processes. 

(6) The silver image is treated with a bleach, the products of the reaction har- 
dening or tanning the adjacent gelatin. The unhardened gelatin is then washed 
away with warm water and the remainder dyed. This is used in the production 
of matrices for polychrome imbibition work but has found little application as a 
monochrome method. 

(c) The silver image is treated with a bleach and the product of the reaction 
dissolves the adjacent gelatin which is washed away and the remainder dyed. 
This process has found little application and is of interest merely because it com- 
plements the tanning processes. In this case a positive dye image will be ob- 
tained from a negative silver image. 

(4) Color Development. (a) Color development with color formers. Here, 
the oxidation product of the developing agent is an insoluble dye which is co- 
precipitated with the developed silver image. Examples are leuco indigo and 
leuco thioindigo. 

(6) Coupling color development in which the oxidation products of the de- 
veloping agent couple with a compound that may be present either in the de- 
veloper or in the emulsion to give a comparatively insoluble dye. These dyes are 
frequently, but not necessarily, of the indophenol or indamine class. 

In the previously outlined methods, excepting color development 
the film must first be developed to a black-and-white image before 
it can be colored. In most cases where direct toning baths of the fer- 
rocyanide type are used, the film is developed, fixed, washed, and 
dried normally, that is, as a black-and-white print and then later 
toned, washed, and dried. 

While the outline given above does not touch all of the available 
methods for producing a colored photographic image, most of the 
processes in actual use are variations of the above systems. The 
methods described under the heading of color development have in 
the past been applied almost exclusively to two or three color proc- 
esses. However, they offer several advantages for the production of 
toned monochrome images as well and it is the latter of these methods, 
the dye-coupling method, that is to be discussed. The obvious saving 

414 K. FAMULENER [j. s. M. P. E. 

through such a system is the elimination of the multiplicity of opera- 
tions generally associated with toning. Here it is only necessary to 
develop the film, fix it, wash it, and dry it. This, of course, yields 
an image consisting of metallic silver and a relatively insoluble dye. 
In most natural-color processes where color development is used, the 
final result is a pure dye image, the silver being removed with a bleach 
such as Farmer's reducer after color development. However, in the 
case of monochrome color development the silver is left in the film. 
This does not greatly detract from the color values since the silver 
contributes most to the high densities where colors normally are not 

In 1912 Fischer patented 2 and in 1914 Fischer and Siegrist pub- 
lished 3 the process of producing colored photographic images by the 
use of dye-coupling development. In his patent Fischer outlined 
the chemistry of the process and covered quite broadly the type of 
compounds that could be used. The developing agent was a para- 
phenylenediamine or paraaminophenol ; the specific compound men- 
tioned in his example being diethylparaphenylenediamine, otherwise 
paradiethylaminoaniline. The coupling agents used were phenols 
such as alpha napthol, amines, or in fact compounds having an active 
methine group such as acetoacetic ester, benzyl cyanide, and phenyl- 
methylpyrazolone. An excellent review of their work as well as that 
done more recently by the Schinzel brothers 4 has been given by Fried- 
man. 8 

When the problem of dye-coupling development of cine positive 
was undertaken diethylparaphenylenediamine was used as the de- 
veloping agent and alphanaphthol as the coupler to produce a blue 
image; acetoacetanilide, and later dichloracetoacetanilide to produce 
a yellow image, and phenylmethylpyrazolone to produce a magenta 

Certain characteristics of the process became apparent immedi- 
ately. One was that a developing time approximately double that 
used for normal black-and-white positive work is necessary to obtain 
a contrast and density approaching that of black-and-white positive 
development. Another was that the usual hypo, acetic acid, sulfite, 
alum hardening, and fixing bath could not be used without bleaching 
the dye image. This was most noticeable with the yellow image and 
to a less extent with the blue and the red. It was found that a special 
hardening bath had to be used. This consisted of hypo, sulfite, and 
alkaline formaldehyde. It was necessary to use the formaldehyde in 


in order to harden the film sufficiently to withstand machine proc- 

Two problems had to be overcome before this process could be said 
to have any value. First, methods of blending the colors to obtain 
intermediate tones had to be worked out, and, second, the contrast 
of the process had to be increased before it could be applied to motion 
picture positive work. 

Several methods of blending colors have been arrived at. It was 
found that various coupling agents could be combined in the same 
bath and intermediate tones would result. However, the ratio of 
the concentration of the various coupling agents present did not bear 
any direct relation to the color that would be formed. For instance, 
in producing a green far more dichloracetoacetanilide than alpha 
napthol had to be used. 

While the combining of coupling agents produced fairly good re- 
sults, another and more flexible method was worked out. This con- 
sisted of using three independent color-forming developer solutions : 
a magenta, a blue-green, and a yellow. By developing the film in 
these solutions, almost any color desired could be obtained. The 
film could be either completely developed in one of these solutions 
or started in one and completed in a second; or even started in one, 
carried on in a second, and completed in a third. Then, by varying 
the time of development in each of the solutions used, the color tone 
of the final positive could be controlled to make a long range of colors 
available under reproducible processing conditions. This method of 
obtaining a range of colors seems particularly desirable when applied 
to machine processing", since with three solutions in the developing 
line a change-over from any color to any other color is possible without 
compounding new formulae. In a machine thus adapted to color 
development it is only necessary to vary the number of strands im- 
mersed in each color developer. As an example a green image is formed 
by developing the positive for 2 x /2 minutes in the blue-green color 
developer and then continuing in the yellow developer for 4*/2 minutes. 
It is interesting to note that equal times of development in two de- 
velopers did not produce the same hue when the order of development 
was changed. For instance, by developing for 3 x /2 minutes in a blue 
developer and then an equal time in a magenta developer, a redder 
image was obtained than if development was started in the magenta 
developer and completed in the blue developer. This effect was to 
be expected since we know that when a film is placed in a developing 



[J. S. M. P. E. 

solution there is a certain inertia period before the image begins to 
become visible. Since this inertia has to be overcome in the first 
solution and not in the second solution, we would expect the tone of 
the second solution to predominate and this has been found to be true. 

Either of the methods outlined above, that is, the combination of 
two or more color-forming compounds in the same solution or sequen- 
tial development in three color developers producing subtractive 
primaries can be used and have been used to produce a variety of 

The remaining problem was to obtain sufficient contrast for positive 
work. This was attacked in three ways. First, the inclusion of a high- 

BLUE 1.65 
RED 1.71 
YELLOW 1.67 


FIG. 1. Two-bath color-coupling development. 

contrast developing agent in the coupling developer solution was 
tried. Hydroquinone proved quite satisfactory for this purpose and 
did not interfere greatly with the color formation since its action was 
to build up the heavy densities which, even normally, did not show 
brilliant colors. The use of hydroquinorie was applied in two ways. 
The first consisted merely in adding hydro quinone to the single 
solution developer containing both a developing and a coupling 
agent. This yielded quite satisfactory results. 

The second method made use of a two-solution developer in which 
the first solution consisted of hydroquinone, diethylparaphenylene- 
diamine, a weak alkali, and bromide; and the second consisted of the 
coupling agent together with a strong alkali and bromide. It was 


felt that this two-solution system offered several advantages. The 
keeping qualities of the two solutions were very good and uniform 
results could be obtained merely by replenishing the first solution. 
Also, a two-solution system did not unnecessarily complicate the de- 
velopment process since, for the production of different colors, the 
same first solution was used followed by the appropriate second solu- 
tion. Moreover, with a two-solution system an accurate control of 
the time in each solution is not nearly as important as it is when a 
single developer is being used. In most cases the reaction goes to 
completion and the time-gamma curve flattens out, resulting in a 
considerable processing latitude. In Fig. 1 are shown sensitometric 
curves obtained by developing Agfa Cine positive film in three 
different color-forming developers containing hydroquinone. For all 
these curves the developing time in the first solution is three minutes 
and in the second, five. The temperature of the solutions is held 
constant at 70F. 

A third method that has been used to control the contrast and one 
that is more of experimental interest than practical value follows: 
The positive was developed to a normal black-and-white silver image, 
fixed, and washed as usual. It was then bleached in a solution that 
converts the image to a silver salt and flashed with white light. The 
film was then re-developed in the color-forming developer. This 
gave excellent results but was, of course, a long process quite similar 
to dye toning and other common toning procedures. As such, it 
offers but slight advantage over the commoner methods. Of course, 
it has the general advantage of all these color development methods 
in that a wide range of tones is possible. Also, the contrast presented 
no difficulty since the reaction goes to completion in the second de- 
velopment and the contrast obtained through the first, i. e., black-and- 
white development, was maintained throughout the rest of the process. 

Following the presentation of the paper a demonstration reel made up of scenic ma- 
terial color developed to appropriate tones was shown, to demonstrate the result of 
direct color-coupling development. Five different solutions were used to obtain the 
five tones shown. Alpha naphthol, dichloracetoacetanilide, and phenylmethylpyrazo- 
lone were the couplers. For the red and red-brown tones phenylmethylpyrazolone 
and dichloracetoacetanilide were combined; different proportions being used to obtain 
the two colors. 


1 NICHOLAUS, J. M.: "Toning Positive Film by Machine Methods," J. Soc. 
Mot. Pict. Eng., XXIX (July, 1937), p. 65. 

2 D. P. 253,335. 


3 FISCHER AND SIEGRIST: "Uber die Bildung von Farbstoffen durch Oxydation 
mittels belichteten Halogensilbers," Phot. Korr., 51 (1914), p. 18. 

4 SCHINTZEL, K. AND L. : "Dreischicht-Farbenphotographie durch gleichzeitige 
Dreifarbenentwicklung," Das Lichtbild, 12 (1936), p. 919. 

6 FRIEDMAN, J.: "Photographic Review," Amer. Phot., 31 (1937), p. 446. 


MR. CRABTREE : When mixed couplers are used in the single developers does 
not the hue change with exhaustion? 

MR. FAMULENER: We did not run any direct exhaustion tests. It is possible 
that that would take place, but the problem can generally be handled by raising 
the concentration of the coupling compounds beyond the exhaustion limit one 
would normally expect, allowing the developing agent rather than the coupling 
agent to regulate the exhaustion. 

MR. CRABTREE: Another difficulty, of course, is in being sure that the projec- 
tion contrast is correct by the time you have got the hue that you want. 

MR. FAMULENER: This problem is handled as in black-and-white work, by the 
proper formulation of the developer and the determination with light-test strips 
of the correct printing exposure. 

MR. CRABTREE: And assuming that you are replenishing correctly. 

MR. FAMULENER : In the course of the work we did make some sensitometric 
studies, but we felt sensitometry would tell us little because the psychological ef- 
fects of the color on the screen are more important to the observer than the theo- 
retically desirable contrast obtained on a sensitometric strip. 

MR. PRESGRAVE : Is it possible to do double-toning in this way, by a combina- 
tion of developing black-and-white first? 

MR. FAMULENER: We did no work on that. Undoubtedly it could be worked 
out, but I do not care to give an answer without doing further experimental work. 

MR. TOWNSLEY: Have you done any work on the negatives? 

MR. FAMULENER: Are you thinking of using it for fine-grain development? 
We did not run any exhaustive tests, and I do not believe there is any reason to 
believe that you would get any finer grain with dye-coupling than by using an 
ordinary paraphenylenediamine developer. If you bleach out the silver and use 
only the dye as the image the contrast drops so low it is difficult to get a printable 

MR. TOWNSLEY: I will have to disagree with you. I have done some work 
along that line, and have had surprisingly good results. 

MR. FAMULENER : We tried it and had difficulty getting a high enough contrast 
to get a printable negative. 

MR. CRABTREE: I think that if there is any diminution in graininess it is ob- 
tained at the expense of loss in definition, due to wandering of the dye. 

MR. FAMULENER : That is generally true, particularly when the couplers that 
we mentioned are used, because they are slightly alkali soluble, and will wander. 

MR. TOWNSLEY: It is perfectly possible to get less graininess but as you say, it 
is at the expense of contrast. Less graininess does not necessarily mean an in- 
crease in resolving power. 



Summary. During recent years an important problem in major-studio cine- 
matography has been that of following focus. Due to the shallow depth of field in 
modern lenses when used at maximum apertures, it is necessary to alter the focus fre- 
quently during the filming of a scene. In moving-camera shots, which are being 
used with increasing frequency, this problem is naturally aggravated, since both 
camera and players may move. The use of "blimped" cameras for sound pictures 
also aggravates the cameraman's problems, as finder parallax is greatly increased by 
placing the finder outside the camera "bungalow." 

At the Metro-Goldwyn- Mayer Studio these problems have been simplified by the 
use of the semi-automatic follow-focus device. This consists of a finder which is 
both focused and pivoted to correct for parallax as the lens is focused. Individual 
cams coordinate the finder movement with the characteristics of any given lens. 

During recent years the twin problems of following focus and of 
finder parallax have assumed major importance in studio camerawork. 
Whereas only a few years ago the camera was usually stationary, 
and the movements of the actors circumscribed to the plane of best 
focus, today both camera and actors move freely around and through 
the set, often in conflicting directions and with little apparent con- 
sideration of the focal limitations of yesterday. It is no exaggeration 
to state that present-day camera crews, with standard production 
sound camera equipment, are daily called upon to make "follow shots" 
that less than a decade ago would have been considered the province 
of the Akeley camera specialist. 

The difficulty of making these shots has, of course, been increased 
by the restrictions imposed by the use of sound. Where previously 
the finder was mounted close to the photographing lens, today the 
camera must be encased in a sound-proof "blimp." With a blimped 
camera, two courses are possible, neither of which is wholly satis- 
factory. If the finder is mounted in its usual place, directly on the 

* Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 26, 

** Metro-Goldwyn-Mayer Studios, Culver City, Calif. 


420 J. ARNOLD [j. s. M. P. E. 

camera, it must be enclosed within the blimp, and is accordingly 
difficult to view accurately. If the finder is mounted more conveni- 
ently outside the blimp, its separation from the camera lens is nearly 
doubled, and parallax becomes a serious problem. 

Several years ago these related problems came under practical con- 
sideration at the Metro-Goldwyn-Mayer Studio Camera Department. 
It was determined that if they could be solved the necessary research 
would pay concrete dividends in speedier, more efficient production 
and in fewer retakes. 

Since no great progress appeared likely in the realization of a 
genuinely silent camera, it was recognized that sound-proof blimps 
must be considered as a permanent factor. For maximum produc- 
tion convenience, it was decided that finders should be mounted ac- 
cessibly outside the blimps. 

The problem thus became one of coordinating the focal adjustments 
of the camera and finder lenses, and at the same time pivoting the 
finder automatically so that at all settings the fields covered by the 
two lenses should coordinate, notwithstanding that they must be 
over 9 inches apart. Automatic, virtually fool-proof operation, and 
durability were necessarily aimed at, despite the inevitably precise 
nature of the mechanism and adjustments involved. 

These aims have to a great extent been realized in the Metro- 
Goldwyn-Mayer semiautomatic follow-focus finder, which has been 
fitted to all of the studio's forty-odd production cameras, and in daily 
use for the last two years (Fig. 1). The device is not yet fully auto- 
matic, but involves the use of removable cams matched to the 
characteristics of each lens used ; but within this limitation the device 
has proved so accurate that the operative cameraman can depend on 
the focus and position of his finder image to indicate corresponding 
properties in the photographed image. 

The foundation of the device is an erect-image optical finder of 
essentially conventional type. The optical system and prisms used 
in this finder have, however, been designed and ground by the studio's 
engineers, and provide a finder image of considerably greater brilliance 
and clarity than usual. 

Obviously, if the finder image is to be sufficiently accurate to serve 
as a precise visual monitor for the camera image, the focusing move- 
ment of the finder lens must be straight in and out, rather than rotat- 
ing. This is provided by interposing a tubular slip-joint between the 
finder lens and the finder proper. This joint carries no load, however. 



FIG. 1. Camera "blimp" with Metro-Goldwyn- 
Mayer Semi-Automatic Follow-Focus Finder attached. 
Focus is controlled from calibrated dial above Finder. 

FIG. 2. Closer view of Metro-Gold wyn-Mayer Semi- 
Automatic Follow-Focus Finder. Note manner in which 
finder-lens moves straight in and out to focus, and dial 
calibrated for all commonly used lenses. 

422 J. ARNOLD U. S. M. p. E. 

The load is taken up by two rods attached to the lens-mount of the 
finder, and sliding in long friction bearings on the top and bottom of 
the finder housing. 

The camera lenses are conventionally mounted. Following the 
usual practice, the lens-mounts are fitted with precision gear-teeth 
which mesh with a train of gears connected to the focusing control 
outside the blimp. In the lenses used on Metro-Goldwyn-Mayer 
cameras, the teeth of the gear-rings on the lens mounts are cut with 
special precision, to eliminate backlash. 

The gear- train with which these gears mesh leads to a vertical shaft, 
the upper end of which is connected to the focusing control on the 
outside of the blimp, while the lower end actuates the pivoting and 
focusing of the finder. 

These latter movements are coordinated with the focusing of the 
lens by means of a roller-tipped lever working against a cam. The 
cams are made of hardened tool steel, and ground to the precise 
curvature that matches the characteristics of the individual lens with 
which the cam is to be used. The cam is in the form of an approxi- 
mately triangular piece of flat metal, and is held rigidly in place on 
hardened dowel-pins by spring-loaded fasteners. Each cam is 
matched to an individual lens, and is considered as a permanent ac- 
cessory of that lens. Since the other parts of the device are standard- 
ized and built to the highest precision standards, however, any lens 
and cam may be used with equal accuracy on any camera equipped 
for this system. 

It will be evident that since modern studio camerawork makes use 
of lenses of many focal lengths ranging from 24 mm. to 4 1 /2 inches, 
which if conventionally mounted would require different amounts of 
rotation to cover the full range of focal adjustments, the finder-syn- 
chronizing cams for some lenses might attain impractically large pro- 
portions. This has been eliminated by using lens-mounts carrying 
focusing threads of differing pitches for the various lenses. The 24- 
mm., 35-mm., and 40-mm. lenses use a 6-pitch thread; the 50-mm. 
and 75-mm., a 4-pitch thread; and the 4-inch and 4 1 /2-inch a 2 1 /z- 
pitch thread. Thus over a range of focal settings between infinity 
and 2 feet, a 24-mm. lens requires less than half a revolution of the 
controlling handle, while for a similar range a 4V2-inch lens requires 
more than a full revolution of the handle. This has proved a con- 
venience for the assistant cameraman, who usually operates the de- 
vice when following focus. 


The scales for all commonly used lenses are engraved on a single 
focusing dial mounted on the left-hand side of the blimp directly above 
the finders (Fig. 2) . A movable indicator on the control handle ob- 
scures all calibrations except those for the lens being used, minimizing 
the risk of errors. A duplicate dial and control are placed on the right 
side of the blimp for use in cramped quarters, when the assistant can 
not conveniently operate the control from the left side. 

Whenever lenses are removed from the camera, or placed thereon, 
lens, focusing control, and finder mechanisms must all be brought to 
a marked neutral point infinity focus for all lenses before the 
lens can be removed or inserted. The lever working against the 
synchronizing cam is spring-loaded, and automatically bears against 
the cam. As there is no other mechanical connection between the 
finder mechanism and the camera-focusing mechanism, the finder 
may be removed from the camera whenever the director or cinematog- 
rapher may wish it for use in lining up the next shot. Immediately 
the finder is put in place on the blimp, however, lens, focus-control, 
and finder form a single mechanical unit, and operate in exact syn- 
chronism. Probably no mechanism of moving parts can ever be con- 
structed or maintained with such perfection as to be wholly without 
play; but in this device the play is reduced to proportions that are 
too minute to introduce appreciable error into the result on the 
screen. In no portion of the mechanism do the tolerances exceed 
0.001 inch, while in some components, such as lens-mounts and gear- 
ing, tolerances as close as 0.0005 inch are maintained. 

In practice this makes it possible for the cameraman to depend 
upon the indications of the finder as to focus and scene alignment 
without the necessity of opening his blimp, racking over the camera 
and studying the camera image on the ground-glass. The assurance 
this gives to the .camera crew will be obvious. The operative camera- 
man, simply from what he has seen through his finder during the 
making of the scene, is able to state with confidence whether or not 
the focus and framing of even the most intricate follow-focus or 
moving-camera shot was correct. Being able to discover such errors 
immediately on the set, rather than in the projection room the follow- 
ing day, has increased production efficiency and has in several in- 
stances resulted in notable economies. 


F. G. ALBIN** 

Summary. The a-c. interlock motor system used to drive cameras, recording, re- 
recording, and projection machines in synchronism has special advantages in such 
applications as driving projector and camera for projection background process. The 
system is generally started from a central point, such as the recording room, and the 
cameraman does not have means for running his camera independently as is so often 
required for photographing slates, exposure tests, and silent scenes. 

An addition has been made to the system to give it the advantages of the synchronous 
motor system: namely, the facilities enabling the cameraman to operate his camera at 
will at regular speed. The addition consists of a set of relays with control circuits, 
and a frequency-changer and field-exciter set. Normally, the camera motors are con- 
nected to the common interlock system through the relays. If, however, the button 
provided at the camera is depressed, the pilot relay operates the main relays which 
transfer the camera motor circuit to the bus of the frequency-changer and field-exciter 
set. The camera motor is operated as a true synchronous motor. One phase of the 
rotor is short-circuited, and the remainder is excited with direct current and serves 
as the field. The three-phase stator is supplied with three-phase power of a frequency 
that will cause the motor to run at the required speed, the same speed as when driven 
with the interlock system. 

The power developed by the a-c. interlock camera motor when operated as a synchro- 
nous motor is approximately the same as under normal operating conditions. The 
acceleration is typical of small synchronous motors when the power supply is suddenly 
connected. The pull-in torque is superior to the slotted-rotor type of as-synchronous 
motor. The operation of the system is smooth, simple, and efficient, and has, after 
several years of use, proved its value. 

In the production of motion pictures, several types of motor systems 
for driving the cameras, recording machines, and sound or picture 
projection machines in synchronism are in general use. Among these 
types are the following with a brief description of their characteristics. 

(1) The a-c. interlock or selsyn system, wherein the primary and 
secondary winding of each motor is connected in multiple with the re- 

* Presented at the 1938 Fall Meeting at Detroit, Mich.; received October 17, 

** United Artists Studio, Hollywood, Calif. 


spective windings of all the other motors of the system, and the primaries 
are excited by alternating current. 

The secondaries of all motors are thereby electrically interlocked, 
and mechanically driving one motor of the system, called a distribu- 
tor, will cause all of the others to rotate at the same (electrical) speed. 

The interlocking torque decreases with increase of speed, diminish- 
ing to zero at synchronous speed for the frequency of the excitation 
potential. The usual operating speed is approximately 2 / 3 of synchro- 
nous speed. 

The merit of this system is that all motors will remain interlocked 
at all operating speeds, including zero or standstill. 

However, any motor depends upon the distributor, and thereby 
can not be operated independently at will. The inertia of the 

FIG. 1. Non-synchronous distributor. 

system is large in comparison with that of the motor required for the 
camera, and the acceleration is lower than desired for operating a 
camera alone. A small motor, such as a camera motor, may be con- 
nected suddenly to the distributor or system already running at 
full speed without damage, except for introducing a surge in the 
system speed. The camera motor then runs as an induction motor 
with torque toward the synchronous speed. At interlock speed it 
should fall into step with the system, which it often fails to do, but 
runs with a fluctuating speed greater than interlock speed. Thus, 
operation on and off a running distributor is not reliable or completely 

(2) The synchronous motor system wherein by proper choice of fre- 
quency of power supply and gearing ratio or both, the load may be driven 
at the exact speed desired. 

426 F. G. ALBIN [J. s. M. P. E. 

Two or more motors on the same power-supply line run in synchro- 
nism after arriving at the speed synchronous with the line frequency. 
Thereby the cameras, recorders, etc., may be run in synchronism, and 
the system is highly satisfactory when it is not important to be inter- 
locked from zero speed or standstill position. 

(3) Direct-current motors with a-c. interlocking potential obtained 
from the armatures via slip-rings and brushes, as commonly used for 
portable systems. 

The frequency of the interlocking potential is the product of the 
speed and the number of poles. At standstill position, therefore, 

FIG. 2. Relays for transferring stage motor leads from normal 
recording motor system to non-synchronous distributor bus. 

there is no interlock torque, and in this respect, this motor system is 
similar to the synchronous motor system. 

For certain purposes, such as for re-recording, photographing of 
projected background, etc., the a-c. interlock system is indispensable. 
The ability to set the several machines such as camera, projector, 
or playback on start marks at standstill and run them exactly in 
synchronism from the start, is invaluable, and possible only with the 
a-c. interlock system. 

To minimize the variety of motors in use, involve only one system 
for all types of photography and sound recording, except trick work, 
and for general economic reasons, the a-c. interlock system, together 
with a means for driving the camera independently at will, is the con- 
ception of an ideal motor system. 


Alternating-current interlock motors have a 3-phase winding on each 
stator and rotor, constituting the primary and secondary of a trans- 
former. The turn-ratio is approximately unity, so that either may 
be used as primary. If one winding is excited by a 3-phase supply and 
the other connected through external circuits, the speed will approach 
the synchronous speed of any typical induction motor : 

o _ / X 60 

where 5" = Speed in rpm. 

/ = Frequency of 3-phase power-supply, in cps. 
P = Pairs of poles. 

FIG. 3. Showing location of switch with respect to the 
camera (arrow indicates switch). 

As pointed out in a previous description of the a-c. interlock system, 
the motors are operated at approximately 2 / 3 synchronous speed, and 
so geared as to drive the camera normally. By operating the motor* 
synchronously with a frequency 2 / 3 as great as that used for the inter- 
lock system, the same speed is attained as previously. 

To convert the motor into a synchronous motor, one phase of the 
leads to the secondary is short-circuited, and from this common tie 
a large condenser is connected to the third lead. Thus a low-impe- 
dance path for a-c. secondary current is provided in all phases, and 
the motor has torque as a closed secondary induction motor. 



[J. S. M. P. E. 

A d-c. potential is applied across the condenser terminals sufficient 
to pass an exciting current through the secondary windings equal to 
the normal rms. value of the secondary current. The field thus 
formed is the resultant of the currents through the windings of two 

Fig. 1 is an illustration of a machine, called a non-synchronous 
distributor, designed to supply the required 3-phase power at the re- 
duced frequency, and the d-c. excitation power. The capacity of this 
machine is sufficient to supply the en tire, lot, or six production com- 
panies. It consists of a geared slotted-rotor motor driving a fre- 
quency-changer at a speed which reduces 60 cps. to 40 cps. Connected 

fffCC*a*rf toon 

FIG. 4. Diagram of independent camera motor drive. 

to the high-speed shaft of the motor is a small compound- wound d-c. 
generator, producing 30 volts. 

Not illustrated, is a box containing the condensers and a step-up 
transformer. It has been found beneficial to increase the potential of 
the 40 cps. supply to the same value as usual for 60 cps. with a cor- 
responding large current. However, when the field is proportionately 
increased so as to restore the power-factor of the current to unity, 
the current is well within safe limits, especially in view of the inter- 
mittent duty of the motor. The torque of the motor under this con- 
dition is about equal to the maximum provided when operating as an 
a-c. interlock. 

Fig. 2 shows the relays used to transfer the stage motor leads from 
the normal recording motor system to the bus supplied by the non- 
synchronous distributor. The small relay is a pilot operated by a 


non-locking switch at the camera. Fig. 3 illustrates the position of 
this switch with respect to the camera. 

One large relay connects the load to the recording motor system, 
and the other to the non -synchronous distributor. These two relays 
are electrically interlocked so as to insure against simultaneous closure 
of both relays. The pilot relay selects the relay for the circuit desired. 
Fig. 4 is a schematic diagram of the entire system . 

For silent shooting, when no sound recording or other equipment 
is involved, the output of the non-synchronous distributor is trunked 
directly to the stage without relays, and the a-c. interlock motor is 
used on the camera, replacing the "wild" motor and providing su- 
perior speed regulation, quieter operation, and general simplification 
of operations. 

After several years of use of this motor system, it has proved com- 
pletely satisfactory, highly efficient, and superior to any other system 
for general requirements of the several types of shooting used in pro- 
ducing motion pictures in a studio. 

F. G. ALBIN** 

Summary. The machines generally used on the motion picture production sets 
to create wind for pictorial effects are large motor-driven propeller fans mounted on 
floor stands. The noise-level at high velocities is so high that satisfactory sound 
recording of the scene is practically impossible. The size and shape require that the 
machines be placed at such distance that the directivity is not readily controllable. 
The additional hazard to sound recording of causing wind around the microphone 
always exists and, commonly, the desirable microphone placement is sacrificed in 
order to avoid the wind. 

A new wind-machine has been adopted and use for several years with a great im- 
provement realized. It is a centrifugal blower, such as is commonly used in ventilat- 
ing systems. The air is conducted by canvas ducts to the set where the scene is being 
enacted. The ducts are equipped with variously shaped fittings and nozzles so that 
the air stream may be directed as desired. 

It has been found expedient to locate the blower outside the stage building and enter 
the duct through a special portal. Thereby the greatest noise source, the blower, is 
remotely located and insulated from the scene by the walls of the stage building. 
Furthermore, it incidentally serves as a ventilator, supplying fresh air to the scene. 
Measurements of noise-level for various wind velocities indicate improvements up to 
70 decibels in noise reduction. Thus sound recordings of scenes requiring wind are 
made possible where heretofore it was necessary to photograph the scene without 
sound and provide synchronized sound subsequently. 

Many scenes in the production of present-day motion pictures call 
for the creation of artificial wind for pictorial effects by the use of 
wind-machines. The popular types of machine are similar to those 
illustrated in Figs. 1 and 2. These are propellers driven by motors 
mounted on floor stands. Fig. 1 is an airplane type of propeller with 
two blades. Its diameter is about 4 feet, and it operates at speeds 
up to 1200 rpm. Fig. 2 is an improved 3-blade screw type propeller. 
Its diameter is also about 4 feet, and it operates at speeds up to 600 

Wind-machines, in general, have long been obnoxious to the sound 
recorders; first, because of the noise of the machines, and, second, be- 

* Presented at the 1938 Fall Meeting at Detrbit, Mich. ; received October 17, 

** United Artists Studio, Hollywood, Calif. 












[J. S. M. P. E. 

cause of the noise effect of the wind produced above the scene in the 
vicinity of the microphone or striking the microphone. Wind "gags" 
on the microphone minimize the second trouble; but in the event of 

FIG. 3. Doorway used for machine, when more con- 
venient than special portals. 

the first, sound must be disregarded, making necessary subsequent 
synchronization of dialog and sound-effects for the scene. This post- 
synchronized recording seldom equals the original, at best. Further- 
more, a noisy device is distracting to actors, even when recording is 
not involved. 

A new type of wind -machine consisting of a conventional centrif- 
ugal ventilation-system blower 
has been adopted. This machine 
is comparatively large, but by 
virtue of its greater pressure 
enabling it to force the air 
through ducts, the machine may 
be situated remotely from the 
scene, and the noise of the 
machine is no problem. Once 
the installation for a particular 
set is made, the direction of the 
wind may be maneuvered with 

the nozzles more easily than is usually practicable with the pro- 
peller machines. 

The machine is usually situated outside the stage building, and the 
duct enters by way of a portal, as illustrated in Figs. 3 and 4, respec- 

FIG. 4. One of the special portals. 

April, 1939] 



lively. Fig. 3 illustrates a doorway, which is used when more con- 
venient than one of the special portals. 

The loss of insulation occasioned by cutting the entrance through 
the stage wall has not been found serious. Added insulation against 

FIG. 5. Typical installation of branch ducts on a stage. 

noises in the vicinity of the blower is provided, when necessary, by 
blankets around the duct, inside or outside the stage, or both. In- 
sulating blankets around the blower protect the stage from noises en- 
tering through the blower and ducts. 

FIG. 6, Reducers, couplings, and nozzles used with the 

Fig. 5 shows a typical installation of branch ducts within a stage. 
Various fittings such as reducers, couplings, and nozzles are provided, 
a few of which are illustrated in Fig. 6. 

A comparison of maximum velocities obtainable from the several 
types of wind-machines is illustrated by the contour diagram of 



[J. S. M. P. E. 

Fig. 7. The conditions for each of the various instances is indicated. 
In all cases, the motors were operated at practically full speed. The 
velocities were measured by means of a double Pitot tube connected 
with an inclined draft water-gauge. The double Pitot tube auto- 
matically corrects for static pressure, leaving an indication propor- 
tional to velocity pressure, which readings are converted into velocity 
in feet per minute, as illustrated in the figure. The values indicated 
for velocities on the axis are fairly accurate, but due to turbulence, 
the other values represent occasional peak values rather than average 

FIG. 7. Velocity contours of wind from several types of wind-machines. 

values. As a check of these readings, data were also taken with an 

It is evident from Fig. 7 that the velocities attainable with the 
blower are considerably greater than with the propellers. When a 
large nozzle is used, the area covered is much greater than possible 
with the propeller. 

The measured noise-level for the various types is the indication of 
the excellence of the blower as a wind-machine. A sound-level meter 
using 10 ~ 16 watt per sq. cm. as reference level and indicating in terms 
of decibels with this reference, and incorporating a weighting network 
for 70 db. loudness was used. The measured sound-levels with 
maximum speeds were as follows : 

April, 1939] SlLENT WlND-MACHINE 435 


2-blade propeller +76 

3-blade propeller +70 

4-inch pipe on blower +53 

2-inch pipe on blower +54 

1-inch pipe on blower +60 

2-inch pipe on blower +45 
(Reduced speed) 

To reduce the blower performance down to the level of the pro- 
peller, the motor was slowed down, resulting in a lowered noise-level 
and a field-velocity pattern much the same as for one of the pro- 
pellers. The noise-level was then approximately 30 db. lower. The 
chief source of noise is the turbulence within the canvas ducts due to 
corrugations of the duct surface. Additional care in installing these 
ducts, keeping them taut, serves to minimize the noise. 

Small blowers used in this manner have been used with great suc- 
cess when the volume requirements are not as great. Several years of 
use in the production of many pictures have proved the value of the 
blower type of wind-machine. 

Acknowledgment is given to Paul Widliska, of United Artist Prop- 
erty Shop, and to the Carrier Engineering Corporation for their 
assistance in preparation of the material in this paper. 


During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 


A. W. COOK** 

In a previous paper 1 Superpan negative film has been discussed. Since the 
properties of that product are well known, the characteristics of Supreme negative 
will be compared with them, in order that the properties of the newer material 
can be conveniently interpreted in relation to practical experience of the cinematog- 
rapher or photographic technician. 

The introduction of a film having such a radical increase in sensitivity com- 
bined with fine-grain size might be expected to arouse speculation concerning the 
possibility that hypersensitizing might have been employed during manufacture. 
It would appear that such speculation was still furthered because the makers of 
Supreme negative film had announced a method of "dry hypersensitization" with 
mercury vapor. 2 For this reason it must be emphatically stated that the in- 
creased sensitivity of Supreme negative is not attained by hypersensitizing or by 
using the old Superpan type of emulsion "pepped up" or pushed to limits. This 
would only endanger other desirable qualities, especially the fine-grain character- 
istics, for the sake of more speed. On the contrary, Supreme negative has an 
entirely new type of emulsion which incorporates the practical application of 
several new discoveries and developments in the technic of emulsion making. 

In physical characteristics Supreme negative and Superpan negative are iden- 
tical, with a double coating of emulsion on one side of the base, over a gray anti- 
halation layer. The back of the cellulose-nitrate base is chemically treated to 
inhibit any tendency toward the generation of static electricity under certain 
conditions of use. 

In expressing the sensitometric relationship between Supreme negative and 
Superpan negative, the usual .D-Log E curves are used, plotted from strips ex- 
posed in a Type IIJ5 sensitometer employing the standard negative filter provided 
with the instrument. Steps indicated on the Log E axis of the curves represent 
an exposure increment of 100 per cent, and all curves have been corrected for fog 

* Presented at the 1938 Spring Meeting at Washington, D. C.; received 
April 18, 1938. 

** Agfa Ansco Corp., Binghamton, N. Y. 







and optical density of the gray base. It should be understood that the curves 
under consideration illustrate relative values only and are not of individual 
quantitative import. 

The relative inertia speeds of Supreme negative and Superpan negative are 
compared in Fig. 1. The inertia values at A and B are one exposure step apart, 
and from their relative positions it may be seen that the speed of Supreme nega- 
tive, as determined by inertia, is 100 per cent greater than that of Superpan nega- 

In the curves shown in Fig. 2 the points A and B, respectively, indicate gradi- 
ent values of 0.3, arbitrarily selected for the present discussion as a value ap- 
proximating the minimum useful gradient. The exposure values opposite points 
A and B, as indicated by A' and B', are likewise one step apart, and it may be 

FIG. 3. (Left) Agfa Supreme Panchromatic negative exposed at//4.5, 1/40 
sec. ; (right) Agfa Superpan negative exposed at//3.2, 1/40 sec. (Developed 
to same gamma.) 

seen that the speed of Supreme negative determined by the minimum useful 
gradient is 100 per cent greater than that of Superpan negative, and in agreement 
with the relative sensitivity determined from inertia. 

A further comparison of Supreme negative and Superpan negative, by means 
of camera exposures, shows that comparable photographs of the same subjects 
can be made with Supreme negative exposed at//4.5, and with Superpan negative 
exposed at //3.2, using the same shutter opening and camera speed in both 
cases (Fig. 3). The pictorial results from such tests verify the conclusions 
drawn from sensitometric tests, and readily demonstrate that under conditions 
of actual practice Supreme negative requires only half the exposure necessary for 
Superpan negative. 

In practical cinematography the unusual light sensitivity of Supreme negative 
is most advantageous, since, with the same level of illumination required by older 
supersensitive films, it permits the use of smaller lens-stops with materially in- 
creased depths of focus. If the use of a smaller lens-stop is not desirable, the 

April, 1939] 



higher speed of Supreme negative permits a reduction of approximately 50 per 
cent in the set lighting, assuming that all other conditions of exposure remain the 

Supreme negative has a gradation inherently steeper than that of Superpan 
negative, and, when developed to a gamma between 0.60 and 0.70, Supreme re- 
quires about 15 to 20 per cent less developing time. Fig. 4 shows time-gamma 
and time-fog curves for the two films, machine developed in Agfa 17 borax de- 
veloper at 65 F. Because of the steeper gradation of Supreme negative, develop- 
ment can not be based upon the results of developer tests made with earlier types 
of film. This is particularly important if all the advantages of improved film quality 
are to be fully realized. However, if the film is over-developed through error or 
miscalculation, the unusually long scale and high shoulder minimize the tone 



* Supreme 



FIG. 4. Time-gamma curves: Agfa Supreme 
and Superpan negatives. Developed in Agfa No. 
17 borax developer at 65 F. 

distortion that might be expected. Referring again to Fig. 2, the unusual latitude 
is graphically indicated by the long straight-line portion of the characteristic 
curve. In practice, this is manifested by more faithful reproduction of highlight 
or shadow tone values, thus lending greater brilliance to the finished print. 

A survey made among a number of the major laboratories has shown that it is 
rather common practice to base processing technic on the overall-gamma method 
of tone reproduction. 3 Under such a system negatives and positives are developed 
to predetermined gammas, the product of which is the overall gamma selected 
as the value that most nearly reproduces the tonal values of the original subject 
under normal conditions of projection. Since the overall-gamma theory is en- 
tirely valid only when dealing with the straight-line portions of characteristic 
curves, processing control based upon this theory is the more effective in propor- 
tion to any extension of the straight-line response of the negative and positive 
materials in use. With this in mind, the advantages accruing from the use of 
Supreme negative may be readily appreciated. 


Fig. 5 shows spectograms of both Supreme negative and Superpan negative 
films exposed with tungsten light, and it will be seen that the relative color sensi- 
tivities are almost identical. The higher speed of Supreme negative extends 
through the full range of spectral sensitivity, and no alteration is required in the 
make-up normally employed with the older supersensitive films. Factors for some 
of the more commonly used filters are listed in Table I. 


Exposure Multiplying Factors for Wr alien Filters in Normal Daylight 

Filter Used Ultra Speed Superpan Supreme 

Aero No. J 1.5 1.5 1.5 

Aero No. 2 2.0 2.0 2.0 

3N5 4.0 4.0 4.0 

5N5 6.0 5.0 6.0 

K-l 1.8 1.6 1.8 

K-l l / t 2.0 1.8 2.0 

K-2 2.0 1.9 2.0 

Minus blue 2.5 2.5 2.5 

G 2.5 3.0 3.0 

23-A 3.5 4.0 4.0 

25-A 5.0 5.5 6.0 

B 9.0 7.0 9.0 

C-4 10.0 7.0 8.0 

C-5 6.0 6.0 5.5 

F 7.0 7.0 8.0 

N.D. 0.25 1.8 1.8 1.8 

N.D. 0.50 3.1 3.1 3.1 

N.D. 0.75 5.6 5.6 5.6 

N.D. 1.00 10.0 10.0 10.0 

72 20.0 20.0 30.0 

The obvious advantage in speed of Supreme negative over Superpan negative 
has been effected without sacrificing any other essential characteristic. This fact 
is singular when one considers that higher speed has usually been synonymous 
with coarser grain, higher fog, poorer keeping quality, and, in some cases, flatter 
gradation. In fact, from a manufacturing standpoint, the limiting factors in 
speed have been determined by the minimum requirements for each of these other 
important characteristics. In the production of this film, not only have these 
other characteristics been unimpared, but in some cases refined to a degree never 
before realized in super speed films. 

In Fig. 6 are shown enlargements made from single frames of each film. The 
subject photographed was the same in each case and the negatives were developed 
to the same gamma. Some comparison of the grain of the two films can be seen 
from these prints, although it must be acknowledged that in general such a com- 
parison does not necessarily depict the effect as it would appear upon the screen. 
The practical difference as seen in motion projection is in this case, however, of 
the same order as shown here. 

April, 1939] 



This fine grain coupled with unusual sensitivity makes Supreme negative an 
excellent film for the photography of projected background scenes. It allows 

FIG. 5. Mazda wedge spectrograms: (Above) Agfa Supreme Pan- 
chromatic negative; (below) Agfa Superpan negative. 

larger screens of diminished brightness to be photographed with adequate ex- 
posure, or with screens of normal size and undiminished brightness the combina- 
tion shot may be made with a smaller lens-stop, thus increasing the depth of focus 

FIG. 6. Agfa Supreme and Superpan grain comparisons, 20X normal. 

and obviating the necessity for the players to remain inconveniently close to the 
background. Since the film used to photograph projection background shots 
is actually being used as a duplicate negative, it may be seen that the unusually 


fine grain of Supreme negative makes it additionally valuable for this type of 

In perfecting the Supreme negative emulsion, not the least consideration was 
given to its aging characteristics. Before the first regular production was coated, 
several months were spent in studying the aging characteristics of the final ex- 
perimental coatings. These tests were conducted on accelerated and normally 
aged material. It was not until the stability of the film had been proved fully 
equal to that of Superpan negative that it was adopted for production. 


1 ARNOLD, P.: "A Motion Picture Negative of Wider Usefulness," /. Soc. Mot. 
Pict. Eng., XXIII (Sept., 1934), p. 160. 

2 DERSCH, F., AND DUERR, H. : "A New Method for the Dry Hypersensitization 
of Photographic Emulsions," J. Soc. Mot. Pict. Eng., XXVIII (Feb., 1937), p. 

3 MEYER, H.: "Sensitometric Studies of Processing Conditions for Motion 
Picture Films," /. Soc. Mot. Pict. Eng., XXV (Sept., 1935), p. 239. 



A new type of background projection apparatus has been developed using the 
Mitchell sound or eccentric movement identical with the one used in the latest 
cameras, except for some minor details (Fig. 1). 

The principal objectives hi designing this equipment were freedom from main- 
tenance and elimination of excessive noise. Freedom from maintenance is ac- 
complished by elimination of heating of the mechanism and by use of the eccentric 
movement which has relatively little wear. The noise is reduced by the eccentric 
movement since the accelerations are low, due to the use of eccentrics instead of 

It has been found from experience that it is necessary, in order to have steady 
background projection, to have pilot-pins that give positive registration using 
the same holes for projection as used in exposing the original film. Thus the 
present projectors in most studios in Hollywood today are built around a camera 
movement having pilot -pins. The film in this movement is guided through a 
narrow channel composed of very light steel plates which reciprocate in a direction 
parallel to the lens axis in order to push the film on and off the pilot-pins. In 
order to reduce the inertia it is necessary to make the plates as light as possible; 
consequently the spill light that strikes the plates causes them to warp and, in 
time, to require considerable maintenance. The new projector using the eccentric 

* Presented at the 1938 Spring Meeting at Washington, D. C.; received 
April 18, 1938. 

** Mitchell Camera Corp., West Hollywood, Calif. 

April, 1939] 



movement similar to the Mitchell camera movement has a fixed film-race, with 
the pull-down claws and pilot-pins entering the film in this fixed race and moving 
it in the direction of travel only, so that a heavier and more rigid construction 
may be used around the aperture. The movement has also been modified to ac- 
commodate a very large angle of light. The regular pilot-pin bearings have been 
offset downward so that they do not interrupt any of the beam of light, and, at 
the same time, the bearings themselves are removed from the heat so that the 
pins will not freeze, due to oil evaporating from the bearings if subjected to 
excessive heat. 

The present method of illuminating the aperture in order to get a reasonably 
uniform light on the film is to cover an area of several inches in diameter on the 

FIG. 1. Background projector. 

front of the projector and to use only the center portion of this area. This method 
necessarily throws considerable heat on the projector with a corresponding rise 
in temperature, sufficient at times to cause the mechanism to freeze. To overcome 
this difficulty a radiator consisting of a series of fins extending from the edge of 
the usable light-beam, outward in all directions for approximately P/z inches, 
was placed between the lamp and the main body of the projector. This radiator 
defines the light that falls upon the aperture and prevents any spill light from 
falling upon the main body of the projector. The radiator is insulated from the 
main body of the projector by means of a thin disk of relatively poor conducting 
material so that a rather steep gradient is maintained between the radiator and 
projector. The difference of temperature is of the order of 100F across approxi- 
mately Vs inch of non-conducting material. Thus the difficulties caused by ex- 
cessive heating of the mechanism are removed. 


The projector is equipped with an interlock motor and synchronizing device 
for setting the shutter in phase with the camera shutter after interlock has been 

Probably the most interesting question in connection with a projector of this 
type is: "Is the picture steady?" In answering this it can be pointed out that 
the projector has been tested in several of the major studios both visually and 
photographically, and has proved itself capable of projecting extremely steady 
pictures. The machine is at present being used by the Technicolor Motion 
Picture Corporation in some experimental work to demonstrate the possibility 
of process work in connection with their system of color photography, and has 
proved quite satisfactory for such use. 


Photographic Chemicals and Solutions: J. I. Crabtree and G E. Matthews, 

American Photographic Publishing Co., Boston, Mass. (1939), 366 pp., $4.00. 

This is a book that can be recommended unreservedly as filling a need too long 
neglected by photographic writers. While a large portion of the material has 
necessarily been taken from papers published in the SMPE JOURNAL and other 
publications, many original items have been incorporated to form a thorough and 
extremely useful text and reference book. 

An excellent introduction discusses the differences between the British and 
American systems of measurement and the many advantages of the metric system, 
but recommends that both American and metric equivalents be given for all 
formulas for the benefit of those who prefer not to change their present methods. 

Next follows an effective discussion of "photographic" arithmetic, illustrated 
by many examples of conversion of formulas and related topics. 

The chapter on apparatus not only covers numerous types of units but includes 
many useful hints as to the most effective use of these units. Then follows a com- 
prehensive chapter on materials used in the construction of photographic ap- 
paratus of all kinds. 

After these preliminaries and chapters on the importance of temperature con- 
trol and water purity, follows a chapter on the mixing and using of photographic 
solutions. The thoroughness of the treatment of this topic may be gathered from 
the fact that there are 63 pages of concise and accurate information furnished. 

Following chapters on solutions at high temperatures, storage of solutions, and 
substitution of chemicals, is an authoritative discussion of stains and their cause 
and treatment. This is succeeded, logically, by a discussion of the proper clean- 
ing of photographic apparatus and general suggestions and precautions. 

The book closes with an extensive formulary, list of solubilities, a valuable list 
of manufacturers of suitable materials, and an index. The book is well printed 
on high-grade paper and should be on every photographers bookshelf. 


Moderne Mehrgitter Elektronenroehren ("Modern Multigrid Electron Tubes"); 

M. J. O. Strutt, Eindhoven, Holland. Second volume: Electro-Physical 

Foundations, Julius Springer, Berlin (1938), 144 pp. 

The first volume of Modern Multigrid Electron Tubes, published in 1937 dealt 
with their construction, operation, and properties. Its reception by the pro- 
fessional world encouraged Dr. Strutt to prepare this second volume, which 
deals with the electrical and physical fundamentals of electron tubes. 

The first part of this second volume, starting from the laws of electrodynamics, 
derives the characteristics of the tubes from their constructional data. The 
second part deals with the highly complex electron movement in multigrid tubes. 
Not only are screen-grid and pentode tubes, discussed but also hexodes, heptodes, 



and octodes. The second portion contains also detailed descriptions of the 
apparatus and methods developed in the Research Laboratory of the Philips 
A. G. for determining the characteristics of these multigrid tubes particularly in 
their relation to short-wave work. 

Some appreciation of the completeness of this text can be gained from the table 
of contents: (1) Basic equations, mechanical analogies, and units, (2} Electron 
movement in a diode, with and without initial velocity, (3) Electron movement 
in a diode with constant cathode emission temperature, (4) Electron movement 
in a triode, (5) Static tube capacities, (6) The screen grid-plate spacing of an ideal 
tetrode, (7) Applications of the screen grid-plate spacing in high-frequency 
amplifier tubes, high-frequency, mixing, and power-amplifier tubes, (8) Dynamic 
tube capacities, (9} The characteristic tube admittances in the short-wave region, 
(10) The electron time of travel effect in amplifier tubes, (11) Dynamic measure- 
ments of the electron movement in hexodes and heptodes, (12) Electron movement 
in an alternating current field, (13) Dynamic measurements of the electron move- 
ment in an octode, (14) Tubes with a curved electron track, secondary emission 
tubes, (15) Ground-noise and the construction of low-noise-level tubes, (16) 
Comments on electrode temperatures, (17) Appendix, supplementing some com- 
putations in the text. 

The author's very concise and clear representation of the abundant material is 
supported by numerous graphical and pictorial illustrations. 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photo static copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

Acoustical Society of America, Journal 
10 (Jan., 1939), No. 3 

Departure of Overtones of a Vibrating Wire from a 
True Harmonic Series (pp. 161-166) 

Resonance in Certain Non-Uniform Tubes (pp. 167- 

Effect of Physical Size on the Directional Response 
Characteristics of Unidirectional and Pressure Gradi- 
ent Microphones (pp. 173-179) 

Indoor and Outdoor Response of an Exponential Horn 
(pp. 180-183) 

Exploration of Pressure Field Around the Human Head 

During Speech (pp. 184-199) 
Moving Coil Pistonphone for Measurement of Sound 

Field Pressure (pp. 200-202) 

Effect of the Consonant on the Vowel (pp. 203-205) 
Tubular Directional Microphone (pp. 206-215) 

Investigation of Room Acoustics by Steady-State Trans- 
mission Measurements. I. (pp. 216-227) 

Frequency Distribution of Eigentones in a Three-Di- 
mensional Continuum (pp. 228-234) 

Distribution of Eigentones in a Rectangular Chamber at 
Low Frequency Range (pp. 235-238) 

Apparatus for Acoustic and Audio-Measurements (pp. 

American Cinematographer 

19 (Dec., 1938), No. 12 

Three New Eastman Negative Emulsions : Background 
X, Plus X, and Super XX (pp. 487-490, 525) E 




C. P. BONER, H. W. 











Howard Greene Awarded Photographic Honors for Oc- 
tober (pp. 494) 

20 (Jan., 1939), No. 1 
Securing Uniform Results with Meters on Interiors (pp. 

6-7) D. B. CLARK . 

Technical Progress in the Past Year (pp. 8-10, 46) W. STULL 
New Tests Coordinate Make-Up (pp. 11-12) G. GAUDIO 

Stills from 8-Mm. Film (pp. 21-22, 45) R. W. TEOREY 

Telco Begins Production (pp. 31-32) I. B. HOKE 

Art Reeves Offers First Independent Re-Recorder (p. 33) 

20 (Feb., 1939), No. 2 
Make-Up and Set Painting Aid New Film (pp. 54-56, 


Gadgets for the Moviemaker (pp. 57-58, 87) R. W. TEOREY 

Metal Film Steadily Progresses (pp. 59-60) R. W. CARTER 

Lighting the New Fast Films (pp. 69-70) 
Photophone Soundheads Provide Studio Presence (pp. 

British Journal of Photography 

85 (Nov., 25, 1938), No. 4099 
Progress in Colour (pp. 744-746), Pt. I 

85 (Dec. 9, 1938), No. 4101 
Progress in Colour (pp. 773-774), Pt. II 

85 (Dec. 23, 1938), No. 4103 
Progress in Colour (pp. 804-805), Pt. Ill 

British Kinematograph Society, Journal 
2 (Jan., 1939), No. 1 
Demonstrations of New Apparatus (pp. 47-53) 

Cinematographic Francaise 

21 (Nov. 25, 1938), No. 1047 

L'Ultra-Cinema a fait de nouveaux progres (High 
Speed Motion Pictures Progress, 3000-4000 Frames 
per Second) (pp. II-IV, VII) 


18 (Dec., 1938), No. 12 
A Bibliography on Recording (pp. 22, 27) J. G. SPARLING 


11 (Dec., 1938), No. 12 

A Laboratory Television Receiver VI (pp. 17-19) D. G. FINK 
Thermionic Emission in Transmitting Tubes (pp. 22-25, 

32) C. P. MARSDEN, JR. 

Spherical Tank U H F Oscillator (pp. 26-28) H. E. HOLLMAN 

Characteristics of Phosphors for Cathode Ray Tubes 
(P. 31) 

April, 1939] CURRENT LITERATURE 449 

12 (Jan., 1939), No. 1 

Initial Drift in Photocells (pp. 15, 32) E. D. WILSON 

Concentric Folded Horn Design (pp. 16, 18) A. J. SANIAL 

International Photographer 

10 (Dec., 1938), No. 11 

Future of Television (pp. 9-11) E. HUSE AND 

New Eastman Emulsions (pp. 23-35, 27) G. A. CHAMBERS 

10 (Jan., 1939), No. 12 
Color Progress Dominates 1939 Technical Horizon (pp. 

9-10) E. GIBBONS 

Telco Bids for Color Recognition (pp. 10-13) 
Why Modern Lamps Are Better (pp. 21-23) P. MOLE 

Projection Symposium (pp. 24-25, 27) W. S. THOMPSON 

International Projectionist 

13 (Dec., 1938), No. 12 
P. A. Units Increasingly Important in Daily Projection 

Routine (pp. 7-11, 29-30) A. NADELL 

Studio Projection: Routine, Methods and Equipment 

(pp. 12-16) M. CHAMBERLIN 

The Projectionist's Part in Efficient Economical Sound 
System Installation (pp. 19-21). A. GOODMAN 

14 (Jan., 1939), No. 1 
Matching Various Units of Theatre Public Address 

Equipments (pp. 7-8, 10) A. NADELL 

Technical Data on New RCA Sound Systems (pp. 20- 

Kinematograph Weekly 

262 (Dec. 1, 1938), No. 1650 
A Revolutionary Projector (p. 31) 

262 (Dec. 22, 1938), No. 1653 

Microphones and Their Employment (pp. 23, 28) R. H. CRICKS 

263 (Jan. 12, 1939), No. 1656 

Technical Developments During 1938 (pp. 143, 149) R. H. CRICKS 

263 (Jan. 19, 1939), No. 1657 
Technical Developments During 1938 (p. 68) R. H. CRICKS 


20 (Nov., 1938), No. 11 

Die Bildwandhelligkeit in Filmtheatern (Screen Bright- 
ness in Motion Picture Theatres) (pp. 285-291) H. JOACHIM 
Die Moglichkeiten des Schmaltonfilms (Possibilities of 

Substandard Sound Films) (pp. 292-296) W. PISTOR 

Methoden zur Messung des photographischen Gleich- 
richtereffektes (Methods of Measuring the Photo- 
graphic Rectifying Effect IV) (pp. 296-299) A. NARATH AND 

W. Vox 



[J. S. M. P. E. 

20 (Dec., 1938), No. 12 

Der technische Stand der Stereophonic (Technical Posi- 
tion of Stereophony) (pp. 313-316) 

Fortschritte der deutschen Bildtechnik (Technical Prog- 
ress in Germany) (pp. 317-319) 

Schallplattenwiedergabe im Tonfilm-Theater (Use of 
Sound Records in the Theatre) (pp. 321-322) 

Ein Zweipackverfahren fiir subtraktive Dreifarbenkine- 
matographie Agfa Pantachrom-Verfahren (Bipack 
Method for Subtractive Three Color Motion Picture 
Photography, Agfa Pantachrom Method) (p. 323) 

Synchronlauf von Bild und Ton, insbesondere mittels 
Drehrichter (Synchronization of Picture and Image, 
Particularly by Means of a Synchronizer) (pp. 324- 

Die Aufnahme und Wiedergabe von Reihenbildern mit- 
tels Linsenrasterschichttrager (Taking and Reproduc- 
ing a Series of Pictures by Means of Lenticular Screen 
Films) (pp. 327-328) 

21 (Jan., 1939), No. 1 

Grossbilderzeugung beim Fernsehen (Large Pictures by 
Television) (pp. 1-5) 

Physikalische Problems der Fernaufnahme (Physical 
Problems Encountered in Telephotography (pp. 6-9) 

Mechanische Filterung Bei Tonfilmmaschinen (Mechani- 
cal Filtering in Sound Film Apparatus) (pp. 9-14) 

Plastischer Film (Stereoscopic Film) (p. 15) 

Der elektrische Belichtungsmesser fiir die Berufskine- 
matographie und seine Problems (An Electric Ex- 
posure Meter for Professional Motion Picture Photog- 
raphy and Its Problems) (pp. 16-18) 

Optical Society of America, Journal 

29 (Jan., 1939), No. 1 

A Note on the Color Temper ature-Candlepower Char- 
acteristic of Tungsten Lamps (pp. 16-19) 
A Simple Photox Photometer Head (pp. 35-36) 












Philips Technical Review 

3 (Oct., 1938), No. 10 
Television with Nipkow Disc and Interlaced Scanning 

(pp. 285-291) H. RINIA 

The Diffraction of Light by Sound Film (pp. 298-305) J. F. SCHOUTEN 

Photographic Journal 

78 (Dec., 1938) 

Exhibition of Kinematography (pp. 715-716) 
The Technique of Sound Recording (pp. 727-731) T. S. LYNDON-HAYNES 

April, 1939] CURRENT LITERATURE 451 

Die Photographische Industrie 

36 (Dec. 28, 1938), No. 52 

Grossere Lichtausbeute durch Kondensoren mit Zylin- 
derwirkung (Greater Light Yield by Use of Conden- 
sers that Produce a Cylindrical Effect) (pp. 1441- 

37 (Jan. 25, 1939), No. 4 
Zur Tonaufzeichnung mit ultraviolettem Licht (Sound 

Recording with Ultraviolet Light) (pp. 81-84) A. NARATH 


11 (Dec., 1938), No. 130 
Television Picture Faults and Their Remedies, I (pp. 

717-20) S. WEST 

The Supersonic Light Valve Simply Explained (pp. 734- 

736) M. J. GODDARD 

How the Picture Is Synchronised, II (pp. 741-742) 




Engineering Vice- President Executive Vice-President 

Editorial V ice-President 



Financial Vice-President 




Convention Vice-President 












Chairman, Atlantic 
Coast Section 


Chairman, Mid-West 



Chairman, Pacific 
Coast Section 


(Atlantic Coast) 

*D. E. HYNDMAN, Chairman 

G. FRIEDL, JR., Past-Chairman **H. GRIFFIN, Manager 

*P. J. LARSEN, Sec.-Treas. *R. O. STROCK, Manager 


*S. A. LUKES, Chairman 

C. H. STONE, Past-Chairman *J. A. DUBRAY, Manager 

*G. W. BAKER, Sec.-Treas. **O. B. DEPUE, Manager 

(Pacific Coast) 

*L. L. RYDER, Chairman 

J. O. AALBERG, Past-Chairman *C. W. HANDLEY, Manager 

*A. M. GUNDELFINGER, Sec.-Treas. **W. MILLER, Manager 

Term expires December 31, 1939. 
**Term expires December 31, 1940. 


(Correct to April 1st; additional appointments or changes may be made at 
any time during the year, as necessity or expediency may require,} 






G. FRIEDL, JR., Chairman 


J. I. CRABTREE, Chairman 


R. M. EVANS, Chairman 




W. C. KUNZMANN, Chairman 






O. F. NEU 





F. H. HOTCHKISS, Chairman 


A. W. SCHWALBERG, Chairman 


E. THEISEN, Chairman 

G. F. RACKETT, Chairman 



D. B. JOY 




[J. S. M. P. E. 


D. E. HYNDMAN, Chairman 






E. THEISEN, Chairman 




S. HARRIS, Chairman 





(West Coast) 

L. A. AICHOLTZ, Chairman 



J. G. BRADLEY, Chairman 




J. G. FRAYNE, Chairman 



A. N. GOLDSMITH, , Chairman 


April, 1939] 



E. R. GEIB, Chairman 















R. H. RAY 














New York 








District of Columbia 






























O. F. NEU 

J. S. ClFRE 






















G. D. LAL 




M. L. Mistry 













New Zealand 





[J. S. M. P. E. 


H. RUBIN, Chairman 




































J. HABER, Chairman 



P. A. McGuiRE 








E. K. CARVER, Chairman 































C. W. HANDLEY, Chairman 







A. N. GOLDSMITH, Chairman 




















April, 1939] 




(American Standards Association) 
A. N. GOLDSMITH, Chairman 

S. HARRIS, Secretary 














Officers and Committees in Charge 
E. A. WILLIFORD, President 
N. LEVINSON, Executive Vice-President 
W. C. KUNZMANN. Convention Vice-President 
J. I. CRABTREE, Editorial Vice-President 
L. L. RYDER, Chairman, Pacific Coast Section 
H. G. TASKER, Chairman, Local Arrangements Committee 
J. HABER, Chairman, Publicity Committee 

Pacific Coast Papers Committee 

L. A. AICHOLTZ, Chairman 




Reception and Local Arrangements 

H. G. TASKER. Chairman 















Registration and Information 

W. C. KUNZMANN, Chairman 


Hotel and Transportation 

G. A. CHAMBERS, Chairman 





Convention Projection 

H. GRIFFIN, Chairman 






Officers and Members of Los Angeles Projectionists Local No. 150 

Banquet and Dance 

N. LEVINSON, Chairman 






Ladies' Reception Committee 

MRS. N. LEVINSON, Hostess 

assisted by 








J. HABER, Chairman 



New Equipment Exhibit 

J. G. FRAYNE, Chairman 



O. F. NEU 


Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Special hotel rates, guaranteed to SMPE delegates, European plan, will be as 
follows : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8 . 00 

Parlor suite and bath, 2 persons 12.00 

462 1939 SPRING CONVENTION [j. s. M. P. E. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available 
to those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately 
upon arriving at the Hotel. Convention badges and identification cards will 
be supplied which will be required for admittance to the various sessions, the 
studios, and several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges : 


Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 147.50 23.65 

Detroit 106.75 19.20 

New York 139.75 22.85 

Rochester 124.05 20.50 

Cleveland 110.00 19.20 

Philadelphia 135 .50 22 . 35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips, sixty-day limits. Arrange- 
ments may be made with the railroads to take different routes going and coming, 
if so desired, but once the choice is made it must be adhered to, as changes in the 
itinerary may be effected only with considerable difficulty and formality. Dele- 
gates should consult their local passenger agents as to schedules, rates, and stop- 
over privileges. 

San Francisco Fair 

On February 18, 1939, the Golden Gate Exposition opened at San Francisco, 
an overnight trip from Hollywood. The exposition will last throughout the sum- 
mer so that opportunity will be afforded the eastern members of the Society to 
take in this attraction on their Convention trip. Special arrangements have been 
made with the Hotel Empire at San Francisco for Convention delegates visiting 
the Fair, at the following daily rates: 

One person, room and bath $3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 


Parlor and bedroom for two persons 8 . 00 and up 

Two large bedrooms, each with private bath and a living 

room; for four persons 16.00 

Reservations can be made either by writing directly to the Hotel Empire or by 
addressing Mr. W. C. Kunzmann, Convention V ice-President, Box 6087, Cleve- 
land, Ohio. 

April, 1939] 1939 SPRING CONVENTION 463 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems, and 
arrangements will be made to visit several of the studios. The Local Papers 
Committee under the chairmanship of Mr. L. A. Aicholtz is collaborating closely 
with the General Papers Committee in arranging the details of the program. 

Studio Visits 

On the afternoon of Tuesday, April 18th, Paramount Pictures, Inc., will act as 
hosts of the Convention at their Hollywood Studio. The program will be in 
charge of Messrs. L. L. Ryder and H. G. Tasker. On the afternoon of Thursday, 
April 20th, the delegates of the Convention will be entertained at the studio of 
Warner Brothers First National, Inc., at Burbank. The program of the afternoon 
will be under the supervision of Mr. N. Levinson. 

Semi- Annual Banquet and Dance 

The Semi- Annual Banquet of the Society will be held at the Hotel on Thursday, 
April 20th. Addresses will be delivered by prominent members of the industry, 
followed by dancing and entertainment. Tables reserved for 8, 10, or 12 persons; 
tickets obtainable at the registration desk. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the general office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. N. Levinson, hostess, and the Ladies' Committee. A 
suite will be provided in the Hotel, where the ladies will register and meet for 
the various events upon their program. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 
Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt 


Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Li- 
brary and Art Gallery (by appointment only) ; Palm Springs, Calif. ; beaches at 
Ocean Park and Venice, Calif.; famous old Spanish missions; Los Angeles Mu- 
seum (housing the SMPE motion picture exhibit); Mexican village and street, 
Los Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, 
and Palm Springs, and special tours may be made throughout the Hollywood 
area, visiting the motion picture and radio studios. 


The following are available from the General Office of the Society, at the prices 
noted. Orders should be accompanied by remittances. 

Aims and Accomplishments. An index of the Transactions from October, 
1916, to December, 1929, containing summaries of all articles, and author and 
classified indexes. One dollar each. 

Journal Index. An index of the JOURNAL from January, 1930, to December, 
1935, containing author and classified indexes. One dollar each. 

SMPE Standards. The revised edition of the SMPE Standards and Recom- 
mended Practice was published in the March, 1938, issue of the JOURNAL, copies 
of which may be obtained for one dollar each. 

Membership Certificates. Engrossed, for framing, containing member's name, 
grade of membership, and date of admission. One dollar each. 

Lapel Buttons. The insignia of the Society, gold filled, with safety screw back. 
One dollar each. 

Journal Binders. Black fabrikoid binders, lettered in gold, holding a year's 
issue of the JOURNAL. Two dollars each. Member's name and the volume 
number lettered in gold upon the backbone at an additional charge of fifty cents 

Test-Films. See advertisement in this issue of the JOURNAL. 



APRIL 17-21, 1939 

The Papers Committee submits for the consideration of the membership the follow- 
ing abstracts of papers to be presented at the Spring Convention. It is hoped that the 
publication of these abstracts will encourage attendance at the meeting and facilitate 
discussion. The papers presented at Conventions constitute the bulk of the material 
published in the Journal. The abstracts may therefore be used as convenient refer- 
ence until the papers are published. 

J. I. CRABTREE, Editorial Vice- President 

S. HARRIS, Chairman, Papers Committee 

L. A. AICHOLTZ, Chairman, West Coast Papers Committee 









Report of the Progress Committee; J. G. Frayne, Chairman. 
A summary of advances made during the past year in the various technologic 
phases of the motion picture art. 

"Brief Review of Foreign Film Markets during 1938;" Nathan D. Golden, 
Motion Picture Division, U. S. Bureau of Foreign and Domestic Commerce. 

American motion pictures continued to enjoy widespread popularity through- 
out the world during 1938, although the intensification of difficulties abroad has 
resulted in a drop of 70 to 65 per cent in America's domination of the world's 
motion picture screens. The obstacles encountered have been of diverse char- 
acter, including legislative restrictions, quota systems, high taxes, foreign-ex- 
change controls, occasional excessive censorship, so-called "racial" theories, 
fervent efforts to build up local film industries, active hostilities in the Far East 
and Spain, transfers of territories, and such intangible factors as uncertainty and 

Various significant legislative enactments occurred during the year in Europe. 
Great Britain imposed a new quota system, to last for 10 years. Commencing 


466 1939 SPRING CONVENTION [J. S. M. p. E. 

January 1, 1939. Italy placed the distribution of all films under Government 
monopoly, and because of the severe terms of this decree American picture firms 
have ceased doing business in Italy. In Switzerland was a new decree making the 
importation of motion pictures subject to an import permit from the Interior 
Department. Denmark created a Government agency, the Film Central, to 
distribute all Danish films not distributed by the producer himself or by inde- 
pendent Danish distributors. Notwithstanding the erection of new barriers, 
American films have continued to enjoy a substantial European market. 

The ban on the, importation of American motion pictures into Japan was lifted 
in October, 1938 for a limited number of American films. New South Wales 
established a new Theater and Films Commission and set up new provisions of 
the Quota Act 

Difficulties loomed in Argentina through the introduction of a bill to give 
definite powers of regulation and control to the local Cinematographic Institute ; 
Argentina has also imposed a ban on the importation of advertising matter. In 
Guatemala a new tax was levied against American distributors. Cuba attempted 
to put through an exhibitor's quota, but the bill failed of passage, being wholly 
impracticable in its provisions. 

The Latin American market at present appears to afford a promising oppor- 
tunity to offset the restriction of our picture markets in other parts of the world. 
With 5239 potential theater outlets in that area today, and with new theater 
construction increasing every year, American companies are coming to realize 
that Latin America is a region that should be intensively cultivated. This, it is 
believed, may best be done by producing in Hollywood Spanish-dialog films em- 
ploying stage favorites brought from Latin America and placed in Hollywood 
settings, with the use of reconstructed sets and our proficient American technic. 

During 1938, foreign motion picture production totaled 1706 feature films, 
against 1809 in 1937. The countries of the Far and Near East led in production, 
with 967 features, as compared with 959 in 1937. Production in Europe fell off 
sharply, the total for all Europe being only 609 features. Latin American feature- 
film production increased by 40 films to a 1938 total of 130, Mexico being the 
largest producer, with 60 features. 

Spanish-dialog films have scored notable box-office successes in nearly every 
Latin American country in which they have been shown, locally produced pic- 
tures having often exerted a powerful appeal during the past year, because they 
have portrayed familiar aspects of life, in a language understood by the audiences. 
On the other hand, a wealth of recent evidence demonstrates the grave defects 
and difficulties of the motion picture production attempted in certain countries 
abroad on wholly insufficient foundations. 

"Television Lighting;" William C. Eddy, National Broadcasting Co., New 
York, N. Y. 

Lighting a television production presents many problems peculiar to this new 
field of public entertainment. These problems have necessitated the redesign of 
lighting equipment and the establishment of a simplified technic for handling the 
equipment that differs radically from moving picture practice. 

To cope properly with the lighting requirements of the continuous action se- 
quences, characterizing television productions, a system employing inside silvered 

April, 1939] 1939 SPRING CONVENTION 467 

incandescent lamps in a standardized unit was developed by NBC engineers. 
Based on multiple standardized groups of ! 1 / 2 kw. each, these units are used in 
both the foundation light and modeling equipment of the television studios in 
Radio City, thus insuring quantitative as well as qualitative control of lighting 
by the personnel. 

With cameras generally in motion and an average duration of pick-up from one 
camera a matter of seconds, the problem of modeling in the sets becomes acute. 
This appears to be satisfactorily solved by the technic now in use wherein the 
major interest is centered around the close-up camera. Even this solution, how- 
ever, required new and ingenious equipment to maintain light in the sets and still 
give floor precedence to the cameras and sound equipment. 

While NBC at the present time has appeared to have standardized on the inside 
silvered lamp, exhaustive tests were carried out in an attempt to utilize more 
orthodox equipment. Actual tests under production conditions proved, however, 
that certain requirements of space, weight, and flexibility could not be had with- 
out a serious sacrifice of foot-candles on the set, resulting in the present set-up of 
equipment and personnel that are handling the television lighting assignment in 
the East. 

Under these circumstances, our producers relying on their scientific skill, 
the richness of their facilities and resources, and the variety and range of talent 
available to them in every field will, it would seem, be well advised to stress 
most strongly in the foreign markets the factor of the superior quality of American 
films. We should export only pictures of unquestioned excellence. High quality 
will continue to retain for American motion pictures an exceedingly worth-while 
place in the markets of the world. 

"The Time Telescope;" C. R. Veber, Department of Biophotography, Rutgers 
University, New Brunswick, N. J. 

The Veber time telescope or combination time-lapse and photoelectric exposure 
control machine speeds up imperceptible motion. It is the antithesis of the 
Edgerton time microscope, which covers the other end of the time spectrum. 

This optico-electric robot has both constant and variable (integrated) exposure 
time. The variable-exposure control with exposure modulator gives either a 
gradual change in density, or equal average frame densities regardless of spectral 
or intensity changes in subject lighting. It corrects for failure of film to follow the 
reciprocity law. Photoelectrically regulated, it is the first known camera control 
mechanism that automatically exposes the subject properly regardless of changes 
in color density, area, and average light intensity during or between exposures. 
Long periods of time between exposures make possible the use of a small fixed 
diaphragm (//256), one advantage of the photoelectrically controlled exposure 
time. A photoelectrically variable diaphragm is not good here due to low ex- 
posure range, constantly changing the depth of field. 

Norman McClintock, of Rutgers, in 1933 assigned the author to develop time- 
lapse machines that would eliminate curtains and permit time-lapse photography 
in field and greenhouse as well as in laboratory. Grants by the Chilean Nitrate 
Educational Bureau and Rutgers University made possible the construction of a 
number of machines including the one described here. Fifteen thousand feet of 
time-lapse material has been made in 2 years 40,000 machine hours of operation, 

468 1939 SPRING CONVENTION [j. s. M. p. E. 

the first time-lapse pictures made under natural conditions, and the longest con- 
tinuous run six months. 

Other uses, besides plant growth studies, include time lapse studies of erosion, 
disintegration and rotting, plastic flow, temperature and other changes, corro- 
sion, wear, and pitting. 

"Analysis and Measurement of Distortion in Variable-Density Recording;" 
J. G. Frayne and R. R. Scoville, Electrical Research Products, Inc., Hollywood, 

Types of non-linear distortion in variable-density recording are discussed and 
methods of measurement outlined. The frequency intermodulation method is 
described and applied to film processing for determination of optimal negative 
and positive density and overall gamma. Variance of these parameters from 
classic sensitometric values are traced chiefly to halation effects in film. Use of 
yellow dye in emulsion and fine grain emulsions tend to bridge the gap between 
intermodulation and sensitometric control values. 

"Microphones for Sound Recording;" F. L. Hopper, Electrical Research 
Products, Inc., Hollywood, Calif. 

Factors influencing the choice of a microphone for sound recording are con- 
sidered. The characteristics of a new miniature condenser transmitter and 
amplifier, as well as a number of other types of microphones now in use, are in- 

"A Lightweight Sound-Recording System;" F. L. Hopper, E. C. Manderfeld, 
and R. R. Scoville, Electrical Research Products, Inc., Hollywood, Calif. 

A portable system for production recording, consisting of two main units, is 
described. A mixer, recording amplifier, monitoring facilities, and noise-reduc- 
tion unit are contained in one compact unit weighing 42 pounds. A film re- 
cording machine weighing 100 pounds completes the system, and contains all 
modulator, lamp, and motor controls, as well as film speed indicator and footage 
counter. The power supply may be secured from batteries or a-c. operated 

Report of the Projection Practice Committee, H. Rubin, Chairman. 

A report of the work of the Committee since the last Convention. Work on 
the proposed revision of the NFPA Regulations for Handling Nitrocellulose Motion 
Picture Film has been completed and the revision will be placed before the NFPA 
at the Chicago meeting in May. The present report discusses also the Commit- 
tee's search for practicable and inexpensive light-measuring instruments for use 
in theaters, in addition to other subjects engaging the attention of the several 

Report of the Exchange Practice Committee; A. L. Schwalberg, Chairman. 

A brief account of the work of the Committee during the past year, including 
handling of shipping cases, direction of rewinding film returned from theaters, 
disposition of scrap film, use of lacquer in splicing, etc. 

April, 1939] 1939 SPRING CONVENTION 469 

"A Direct-Reading Photoelectric Densitometer;" D. R. White, Dupont Film 
Mfg. Co., Parlin, N. J. 

A photoelectric densitometer has been built which shows the density of the area 
being measured on a direct-reading scale visible at a reading window. A density 
range from to 3.0 is covered with a reproducibility of approximately 0.005. 
A motor-driven circular neutral wedge is used as the balancing means, and the 
density scale marked on the wedge is read by a stroboscopic flashing light con- 
trolled through a special amplifier system. 

"An Instrument for the Absolute Measurement of the Graininess of Photo- 
graphic Emulsions;" A. Goetz, W. O. Gould, A. Dember, California Institute of 
Technology, Pasadena, Calif. 

The objective determination of graininess is based upon the evaluation of a 
graininess coefficient G defined by the distribution function of the relative trans- 
parency fluctuations ( x = ) : TT (x) = e x . The instrument con- 
\ T m J G 

sists of a microphotometric recorder and a photoelectric integrator. In the former 
unit the ^-fluctuations of a uniformly exposed section of an emulsion are recorded 
with high resolving power and magnification (300 X} by means of a photocell. 
The amplified photocurrent is traced with a high-frequency galvanometer on 
35-mm. film analogous to a large-scale variable-area record. Thus, a true repre- 
sentation of shape and frequency of the ^-fluctuations in the scanned emulsion 
area (width: 30 microns, length: 10 mm.) is obtained in black and white. 

The distribution function of the fluctuations as well as the value of G is ob- 
tained by placing the record on a revolving drum and scanning it by an illumi- 
nated slit. The light transmitted by the record falls upon the photocell, the 
current of which is thus representative of the average occurrence of ^-fluctuations 
for a deviation (AT) from the mean transparency (T m ) determined by the posi- 
tion of the slit on the record. Hence, the change of the photocurrent represents 
the distribution function while the slit is moved across the revolving record. 
The scale on which the photocurrent is measured consists of a family of dis- 
tribution curves (probability integral S-JT(X)'), each being characteristic for a 
certain G-value. The mechanical arrangement is such that a light-beam in- 
dicating the photocurrent selects and follows a particular curve while the slit is 
moved, thus determining whether or not, and if so to what extent, the ^-fluctua- 
tions follow the above distribution function. Furthermore, it indicates the graini- 
ness coefficient in terms of the above function. The taking of a graininess record 
of an emulsion (capable of up to 10 5 fluctuations) takes 3 min., its analysis 2 min. 

"A Multiduty Motor System;" A. L. Holcomb, Electrical Research Products, 
Inc., Hollywood, Calif. 

Various features of motor drive systems now in use by motion picture studios 
are described and the requirements for an ideal system defined. A recently de- 
veloped system is described that will operate efficiently on alternating current 
for stage use or on direct current for location work. Many operating facilities 
are included which a survey has indicated should become a part of any ideal 
motor drive system. 

470 1939 SPRING CONVENTION [j. s. M. p. E. 

"Acoustic Condition Factors;" M. Rettinger, RCA Manufacturing Co., Holly- 
wood, Calif. 

The term "acoustic condition factor" in this paper is used as a general term de- 
scriptive of the acoustic environs of a point in an enclosure. Relationships ex- 
pressed as ratios are given for several quantities, such as "useful" and "harmful" 
sound, direct, and generally reflected sound energy and sound intensity. Curves 
are shown representing loci for partial anti-nodes produced by interference be- 
tween direct and first as well as second reflections in a rectangular room in which 
the sound source is located symmetrically. Equations are given expressing the 
minimal distance between source of sound and microphone for the probable 
avoidance of recording absolute nodes. 

"Recording and Reproducing Characteristics;" K. F. Morgan and D. P. Loye, 
Electrical Research Products, Inc., Hollywood, Calif. 

In the improvement of sound motion pictures, the trend has been to make the 
response of all parts of the recording and reproducing circuits as nearly "flat" as 
possible. In some cases, however, this has resulted in unnatural sound, and 
therefore certain empirical practices have been adopted in the studios and thea- 
ters to make pictures sound best. 

The results of a study are described, the purpose of which has been to evaluate 
the factors affecting the quality of speech as recorded and reproduced, from the 
vocal cords of the actor on the sound stage to the brain of the listener in the 
theater. The characteristics of the various factors have been determined and 
combined with dialog, voice effort, and other equalizers designed to produce an 
overall characteristic "subjectively flat" at the brain of the theater patron. These 
factors, as well as others now in the process of being studied further, are presented. 

One of the most important characteristics studied is that of the change in voice 
quality with a change in effort on the part of the speaker, which is described in 
detail. The stage and set acoustic characteristics, microphone characteristic, 
and dialog equalization to compensate principally for the hearing characteristic 
of the average theater listener, are among the factors discussed. 

"The Polyrhetor, a ISO-Channel Film Reproducer;" G. T. Stanton, Electrica 
Research Products, Inc., New York, N. Y., F. R. Marion and D. V. Waters, 
Western Electric Co., New York, N. Y. 

The creation of a modern Babel might appear to be the purpose of the Poly- 
rhetor, or 150-channel film reproducer, recently completed for the World's Fair 
in New York. Actually, 150 versions of a fifteen-minute story are carefully 
sorted to bring each to only four persons seated in comfortable chairs on a moving 

A verbal description of a diorama along the edge of which the conveyor pro- 
gresses, carefully synchronized with the motion of this conveyor, is given each 
group of persons and is repeated to each succeeding group with approximately 
a six-minute lag. In telling the fifteen-minute story, approximately 150 versions 
are being repeated simultaneously, each version differing only in its starting time. 

In considering possible ways of meeting the elaborate and unheard of require- 
ments established for this sound system, various combinations of disk, film, and 
steel-tape reproducing apparatus were considered, a novel form of film reproducer 

April, 1939 J 1939 SPRING CONVENTION 471 

being selected primarily on the basis of proved operating reliability over long 
periods of time. 

The apparatus is a twenty-ton magnification of the call announcer, the first 
model of which is satisfactorily operating in telephone plants after nine years of 
continuous service. The Poly rhetor consists essentially of a rotating steel drum 
eight feet in diameter, machined to watch-like precision, capable of carrying 24 
continuous film loops past 168 optical scanners and associated amplifiers mounted 
on seven posts equally spaced about the drum. A multiple system of section- 
alized trolleys conveys the sound through sliding contactors to small speakers in 
the cars, around which sufficient acoustical partitioning is provided to avoid pro- 
gram interference from car to car. 

This project presented many problems unique in sound equipment design and 
their step-by-step solution is briefly discussed. 

"Simplifying and Controlling Film Travel through a Developing Machine;" 
J. F. Van Leuven, Fonda Machinery Co., Los Angeles, Calif. 

A developing machine is described in which the drive of the film is frictional 
and the film-carrying rollers are driven on the slack of the film. The first driving 
roller is slightly smaller in diameter than all succeeding driving rollers, thereby 
setting up a tension on the film throughout the machine. 

The upper shaft of film-carrying rollers is held in peripheral engagement with 
the driving rollers by adjustable springs which have a mounting that is yieldable 
downward so that any excess tension on the film draws the film-carrying rollers 
away from the driving rollers until the excess tension has been relieved, which 
allows the film-carrying rollers to be drawn upward by the springs to contact the 
driving rollers again. 

The driving rollers are directly over the upper film-carrying rollers. The 
driving mechanism is completely above the tanks and solutions, and all film- 
carrying rollers in the wet end are mounted individually free and, in turn, are all 
mounted on free-turning tubing or shafting. 

Film-carrying rollers in the dry box, in addition to being mounted on Arguto 
bushings and individually free, are mounted on tubing which in turn is mounted 
with grease-seal ball-bearings on shafting, the entire unit being free to rotate or to 
slide laterally on the shaft, thus becoming self aligning. 

To meet the high initial and maintenance cost of ball-bearings found in film- 
carrying spools, 7V4-inch film-carrying rollers are used throughout. 

Film enters machine in a steady, constant flow. Tension can be altered by the 
operator and, when regulated by adjustment of springs, remains virtually con- 
stant throughout the machine. The steady flow makes great speed possible and 
yet retains a high factor of safety. The machine has the following attributes: 
great simplicity; entire freedom from precision maintenance; film is always under 
even adjusted control and does not slip on rollers; breakage from mechanical 
causes is practically eliminated. 

"A Reel-and-Tray Developing Machine;" R. S. Leonard, Municipal Light and 
Power System, Seattle, Wash. 

A reel-and-tray film-processing system of 7 to 200-ft. capacity, designed to 
overcome deficiencies in existing small-scale film-processing equipment, is de- 

472 1939 SPRING CONVENTION [j. s. M. p. E. 

scribed. Some of the difficulties encountered in its construction are related, and 
a summary given of the results in practice. Advantages listed are, one-man 
operation; cleanliness; economy of solution, because only enough is used to 
develop the film and is then discarded; uniformity of development with any 
quantity of film from 7 to 200 feet; no film damage; no undue aerial or chemical 
fog; clean energetic development with straight H&D curves; and flexibility in 
use or extension to future developments. 

"A New Mobile-Film Recording System;" B. Kreuzer, RCA Manufacturing 
Co., Hollywood, Calif., and C. L. Lootens, Republic Productions, Inc., North 
Hollywood, Calif. 

The design requirements for this type unit and how these requirements were 
met in the selection of truck, body design, equipment layout, etc., are discussed. 
The recording equipment utilized together with the power equipment and other 
special features of the unit are described. This type of unit has been in successful 
operation without revision. 

"An Introduction to Television Production;" H. R. Lubcke, Don Lee Broad- 
casting System, Hollywood, Calif. 

The current television technical facilities of the Don Lee Broadcasting System 
in Los Angeles are briefly described. A mosaic type camera and accompanying 
Don Lee control equipment are used. A coaxial cable conveys the signal there- 
from to the W6XAO sight-sound television transmitters, operating on daily 
schedule on 45 and 49.75 megacycles, respectively. 

The routine of production of a dramatic comedy serial entitled, Vine Street, in 
its thirty-second biweekly episode at this writing, is utilized as an example. A 
total time of twenty hours of one or more members of the dramatic unit is re- 
quired to prepare and present one fifteen-minute episode. 

The sequence of production is as follows: preparation of script; construction 
or modification of props and scenery; cast memorization of lines; cast rehearsals; 
camera-sound, sound-effects, light rehearsal with production staff; make-up; the 
performance itself, including visual-aural introduction of the act ; the performance 
proper with overall supervision of lighting, microphone, and television adjust- 
ments by a television-producer at a distant receiver; closing announcement; 
written and verbal report of errors or advances in technic made during the per- 

Specifications for the physical instrumentalities and the current television 
technic are covered for each of the above factors of production. 

Report of the Television Committee; A. N. Goldsmith, Chairman. 

Partial reports by the two sub-committees: (A) on Television Production and 
Reproduction Technic, O. B. Hanson, Chairman, and (B) Film Properties and 
Laboratory Practice, O. Sandvik, Chairman. The scopes of activity of the sub- 
committees are described, and their program for the coming year. Among the 
items covered by these scopes are (1) glossary, (2) bibliography, (3) tutorial 
material, (4) dimensional practices, (5) normal equipment and procedure, (0) 

April, 1939] 1939 SPRING CONVENTION 473 

special problems such as inter-industry coordination, future equipment needs 
and specifications, etc. 

"A Continuous Type Television Film Scanner;" Peter C. Goldmark, Columbia 
Broadcasting System, New York, N. Y. 

A motion picture film scanner, the first of the continuous type to be used for 
television transmissions, is described. The apparatus was put into operation in 
New York City in the summer of 1937 and has been in use since. In its preferred 
form the scanner projects the image of a continuously moving film onto the 
cathode of a dissector tube. Five images, representing different portions of the 
film in the gate, produced by five stationary lenses, are superimposed one on top 
of the other, while a rotating shutter with concentric slots permits only one lens 
at a time to produce an image. The scanning is accomplished partly by the 
uniform motion of the film and partly by the magnetic scanning of the electron 
image in the opposite direction. The pictures thus obtained are completely free 
from shading, cover a great range of contrast, are free from flicker, and are steady. 
The construction of the scanner is simple and inexpensive. 

"Safekeeping the Picture Industry;" K. W. Keene, Underwriters Laboratories, 
Inc., San Francisco, Calif. 

The purpose of the paper is to deal with a very specialized phase of the motion 
picture industry; that is, its hazards of fire and consequent accident, as due not 
solely but chiefly to the prevalent use of nitrocellulose film. Consideration will 
be given to the causes of hazards and an attempt made to show that they are real 
and what is being done about them. 

The many organizations and groups concerned with and supporting the cause 
of fire prevention and protection in the industry are first described briefly as to 
their basic organization and methods, and are then correlated. 

The publications by these organizations standards, recommended regulations, 
etc. as they bear on the picture industry with respect to the storage, handling 
and use of nitrocellulose film and the equipment associated therewith, are works 
not of one man or even of one group of men, but instead reflect the best opinions 
obtainable from a cross-section of all the industries and groups who are interested. 
The rules, so to speak, are formulated democratically. 

All the many forces pitted against the common enemy, fire, are sincere, and it 
should be cause for pride that our American institutions manufacturer, utility, 
insurance, government, education, association, etc. support this cause unhesi- 
tantly and generously in time and money. 

As distinguished from the recommended Regulations of the National Board of 
Fire Underwriters and the National Fire Protection Association, which in general 
specify the safe methods of installation and use of and needed safeguards for 
apparatus and equipment in the field, the Standards of Underwriters' Labora- 
tories specify the safe construction and performance of apparatus and equipment 
and are applied and "policed" in the producing factory. 

The paper concludes with a discussion of some of the underlying considerations 
affecting the Standards of Underwriters' Laboratories as applied to projectors, 
rewind machines, sound amplifiers, speakers, etc. 

474 1939 SPRING CONVENTION [j. s. M. p. E. 

"RCA Aluminate Developers;" J. R. Alburger, RCA Manufacturing Co., 
Camden, N. J. 

A fundamentally new principle in design of photographic developers has been 
investigated and found to afford many worthwhile characteristics, chief of which is 
the effective self-replenishing property of the developer solutions. Application 
of the new principle to developer solution makes it possible to develop about eight 
times the quantity of film as would be possible under ordinary conditions. The 
principle may be applied to any developer. 

"Push-Pull Class A-B Sound Track;" C. H. Cartwright, Mass. Inst. of Tech., 
and W. S. Thompson, RCA Manufacturing Company, Inc., Hollywood, Calif. 

After an explanation of the term Class A-B and a brief specification of such a 
recording system, the general requirements for the operation of any Class A-B 
system are given and illustrated. 

Differences between the operation of push-pull photocells and push-pull 
vacuum tubes are pointed out and explained, and a discussion of the relative 
advantages of Class A, Class A-B, and Class B push-pull tracks is given. 

"A High-Intensity Arc for 16-Mm. Projection;" H. H. Strong, Strong Electric 
Co., Toledo, Ohio. 

A short description of a high-intensity reflector type projection arc lamp and 
associated rectifier equipment, designed as a light-source for 16-mm. projectors. 

"The Status of Lens Making in America;" W. B. Rayton, Bausch & Lomb 
Optical Mfg. Co., Rochester, N. Y. 

When the modern optical industry was born, this country was predominantly 
agricultural. Its principal industrial developments related to transportation. 
It was natural, therefore, that Europe should have gained great prestige in the 
field of optics in the final quarter of the nineteenth century. 

With the turn of the century, however, agricultural developments had about 
reached their limit and industrial activity began to occupy a larger place in 
American life. Along with others the optical industry felt the incentive to 
greater activity and the first fifteen years of this century saw a rapid advance in 
the magnitude of the industry and improvement in the quality of its product. 

We were still, however, completely dependent on European sources of supply 
for our optical glass and for some of the small-demand class of laboratory in- 
struments. Then came the war that not only cut off all aid from Europe but 
ultimately led Europe to our doors with appeals for optical munitions. 

The war only hastened what would have been inevitable anyway, viz., the 
complete independence of America in optical matters. 

The American optical industry has now reached a point where its raw materials 
(optical glass) and its technical skill recognize no superiors. It can make any 
practical optical element or instrument for which quantitative specifications can 
be written. 

"Notes on French 16-Mm. Equipment;" D. R. Canady, Canady Sound Ap- 
pliance Co., Cleveland, Ohio. 

April, 1939] 1939 SPRING CONVENTION 475 

A brief resume of French substandard projection equipment of unusual design 
including a general description of a practical application of the new water-cooled 
mercury-vapor lamp to 16-mm. projectors. Mention is made of an interesting 
projector that employs no sprockets, automatically adjusts the size of the loops, 
and reduces film wear to a minimum. 

"New 16-Mm. Recording Equipment;" D. R. Canady, Canady Sound Ap- 
pliance Co., Cleveland, Ohio. 

A description of new 16-mm. equipment, including recorder, film-phonograph, 
and a new 35-mm. to 16-mm. reduction printer. 

"The Present Technical Status of 16-Mm. Sound-on-Film;" J. A. Maurer, 
Berndt-Maurer Corp., New York, N. Y. 

Improvements hi the technic of recording and printing during the p^ast few 
years have made possible the production of 16-mm. sound-films, either by optical 
reduction or by direct recording, having considerably better quality than is being 
obtained in general commercial practice. By the use of a moderate degree of 
equalization in recording, it is practicable to obtain from 16-mm. negative prints 
giving a flat frequency response to 6000 cycles, with useful response to 7500 
cycles, when reproduced through a flat amplifying system. Harmonic and 
envelope distortion and speed variations can be kept within acceptable limits for 
high-quality reproduction. The principal remaining defect is background noise. 
Some general agreement upon commercial 16-mm. reproducing system characteris- 
tics is needed, however, before this improved quality can be made generally 

"The Preservation of History in the Crypt of Civilization;" T. K. Peters, 
Oglethorpe University, Ga. 

The problems confronting the scientist who inaugurates the unique task of 
preserving in film for the people of the 80th century a complete picture of our 
life in America today; the problem of the life of film and of its relationship to an- 
cient papyrus that has come down to us over sixty centuries; the method of pre- 
serving it; the microfilming and preparation of the records; the making of a 
duplicate film on metal; and the entire scope of the project is set forth and dis- 

"New Frontiers for the Documentary Films;" A. A. Mercey, United States 
Film Service, National Emergency Council, Washington, D. C. 

The motion picture today is the legacy of experimentation of the past. The 
ancient Egyptians indicated movement in their processional hieroglyphics; 
the Greeks suggested movement in the magnificent friezes on the Parthenon. 

Muybridge's famed experiment with twelve cameras to catch the movements of 
a horse was antedated by experimentation of centuries before. Kircher with his 
magic lantern in 1640, Peter Mark Roget, Sir John Herschel, von Stampfer, Sellers, 
Heyl, the great Faraday, Daguerre, and Niepce these and others worked and 
contributed to establish in practicality the law of persistence of vision with 
regard to moving objects. 

476 1939 SPRING CONVENTION [j. s. M. P. E. 

From the still camera to the movie camera, man moved into new realms of 
record and drama. Thus was evolved the fade-out, the close-up, special light- 
ing, dissolves, and process shots. We had the Melies, the Lumieres, the Griffiths, 
and the deMilles contributing to early production technics. 

The documentary is one of our oldest movie forms, for it means factual photog- 
raphy with the impact of drama. The documentalist takes real people in real 
places. The 15 years from Flaherty's Nanook of the North to Lorentz's The 
River represent years of advance in engineering ; but those working in the medium 
recognize many unsolved problems of sight and sound. 

The problems of modern life open exciting possibilities for both the producer 
and the engineer problems that will mean new developments in the science of 
the motion picture. We have great frontiers ahead in the production of docu- 
mentaries on housing, recreation, the business of food distribution, the problem of 
raising and obtaining food, communications, the conservation of natural resources, 
the backgrounds and rumors of war all these offer a challenge to both the engi- 
neer and the producer, for in working together they will contribute much to a 
great art and a great science the modern motion picture. 

"A New Magnetic Recorder and Its Adaptations;" S. J. Begun, Brush Develop- 
ment Co., Cleveland, Ohio. 

A magnetic recording machine is now commercially available, using an endless 
steel tape loop as a recording vehicle. Such an endless loop makes it possible to 
record and reproduce without reversing the direction of rotation of the mecha- 
nism. Neither is it necessary to manipulate the recording and pick-up heads. 

The simple operation of the unit makes it not only ideal for educational pur- 
poses, but also makes it very adaptable where a signal is to be repeated to a great 
number of times, or where reproduction is required shortly after recording, and 
where only the one reproduction is required. The same machine, with simple 
modifications, adapts itself to a great number of uses. 

Exhaustive tests have been conducted to determine the life and the durability 
of the machine, under very severe conditions, and when operated by a layman. 
The results of such tests have been in every degree satisfactory. 

"Lamps and Optical Systems for Sound Reproduction;" F. E. Carlson, General 
Electric Co., Cleveland, Ohio. 

Sound reproduction systems are designed on the premise that the sound-track 
will be illuminated by a scanning-beam of substantially uniform flux density. 
This paper presents results of extensive studies of the actual beam characteristics 
for all types of optical systems and lamps employed in the reproduction of sound 
from film. They were made possible by a unique microphotometer, designed by 
the author, with which the scanning beam can be analyzed in minute elements. 

The studies cover: Relative levels of scanning beam illumination; effect of 
source displacement from design position on total flux at the sound-track; micro- 
photometer recordings of distribution of flux density across the beam as affected 
by optical systems and source forms and by displacements of the source. 

Report of the Studio Lighting Committee; C. W. Handley, Chairman. 
An explanation is given of lighting problems from the viewpoint of the cine- 
matographer. Certain advances in equipment and working tools remain in 

April, 1939] 1939 SPRING CONVENTION 477 

obscurity for a long period before they find their rightful places in motion picture 
set lighting because they seem to interfere with dramatic effect. If they possess 
merit, however, they are gradually adapted to general use. A typical example 
is the light-meter, which is now going through the final stages of assimilation to 
studio lighting technic. New fast films have been brought into use and the 
resulting changes hi lighting technic are now in the process of perfection. Recent 
changes in lighting equipment are described. Three new higher-speed negative 
films for the Technicolor process are being used. The effect of the new films 
on Technicolor set lighting is explained. 

"Further Improvements in Light Record Reproducers and Theoretical Con- 
siderations Entering into Their Design;" A. L. Williams, Brush Development Co., 
Cleveland, Ohio. 

Direct recording is becoming commercially more and more important. Acetate 
blanks are used for high-quality recordings, but these materials are essentially 
softer than pressed records, and therefore make necessary new considerations 
in the design of a high quality pick-up to be used with them. 

It is shown that a dynamic stylus pressure of approximately 25 grams is the 
maximum force that acetate can tolerate without permanent deformation of the 
modulated grooves, even when due consideration is given to the proper matching 
of stiffness and inertia of the vibratory system of the pickup. A simple formula 
is given for the most suitable condition of the matching of inertia and stiffness 
for a complex wave-form. 

Other factors that interfere with the construction of a light pick-up, such as 
uneven record and turntable surfaces, are explained, and suggestions are made 
for the reduction of these effects. The advantages of "constant amplitude" as a 
method of recording and reproduction, are shown, and a constant amplitude sys- 
tem is demonstrated. 

"Application of Motion Picture Film to Television;" E. W. Engstrom and G. L. 
Beers, RCA Manufacturing Co., Camden, N. J. 

Motion picture film will form an important part of programs for television 
broadcasting. Film projectors for this use are required to meet a number of 
conditions peculiar to television. Methods for projecting and utilizing motion 
picture film are outlined. A specific film projector and associated television 
channel are described in some detail. 

In establishing a technic for producing films most suitable for television, equip- 
ment is needed to interpret properly the final results. Apparatus that will be 
used by broadcasting stations is described. A simpler system has been designed 
that may be useful for the specialized service of gauging the merit of films for 
television. This is described and its operation indicated. 

Some very preliminary observations are included on the characteristics of films 
that have given good results in experimental work and in field tests. 

"Television Studio Technic;" A. Protzman, National Broadcasting System, 
New York, N. Y. 

The studio operating technic as practiced in the NBC television studios today 
are discussed and comparisons are made, where possible, to motion picture tech- 

478 1939 SPRING CONVENTION [J. S. M. p. E. 

nic. Preliminary investigations conducted to derive a television operating technic 
revealed that both the theater and the motion picture could contribute certain 

The problems of lighting, scenic design, background projection, and make-up 
are discussed, with special emphasis on the difficulties and differences that make 
television studio practice unique. 

An explanation is given of the functioning of a special circuit used in television 
sound pick-up to aids in the creation of the illusion of close-up and long-shot sound 
perspective without impracticable amount of microphone movement. The paper 
concludes with a typical television production routine showing the coordination 
and timing of personnel and equipment required in producing a television pro- 

"Methods of Using and CoSrdinating Photoelectric Exposure-Meters at the 
20th Century-Fox Studios;" D. B. Clark, Twentieth Century- Fox Studios, Holly- 
wood, Calif. 

Consistency in negative printing values is one of the most desirable single factors 
in modern cinematography. Photoelectric light-measuring devices can help the 
cinematographer maintain such consistency to a far greater degree than is possible 
otherwise. Not only tests, but actual production have shown that with the proper 
use of these instruments, the entire output of the studio's camera staff can be so 
coordinated that, almost without regard to the photographic conditions prevailing 
on the set, all negative will print correctly within a range of three or four printer- 
light adjustments. 

To make this coordination possible, several requirements must be recognized. 
Among these are a dominant, and by no means completely fulfilled demand for 
photocell meters of unfailing consistency; i. e., meters that are not subject to error 
from photocell fatigue, changes in humidity or temperature, and the like, and are 
sufficiently uniform that all the studio's meters may be expected to give uniform 
readings under any given conditions. 

While these requirements are not wholly met in existing meters, it has been 
found possible to use such meters to advantage. Coordination is effected by use 
of a special, portable testing unit of the photometer type. In this a standard 
light-source is used in circuit with a battery and milliammeter, and controlled by 
a rheostat. When the light is brought to known intensities by the application of 
known currents, the photocell meter being tested must, if accurate, give pre- 
determined readings. 

Further logical developments, predictable on the basis of existing knowledge or 
equipment, should include complete acceptance of strict time-and-temperature 
methods of negative development and some form of automatic, photoelectric-cell- 
controlled print-timing. This would remove all variables, including human 
fallibility, from the processing problem, and leave the responsibility for results 
solely in the hands of the cinematographer, who would in turn be guided by his 
meter in keeping within the tolerances imposed by film and processing, and in his 
efforts to turn out consistently ideally exposed negative. 

April, 1939] 1939 SPRING CONVENTION 479 

"20th Century Silent Camera;" G. Laube, Twentieth Century- Fox Film Corp., 
Hollywood, Calif. 

The camera operates without any sound-proofing box or blimp, weighs sixty 
pounds and is the first instrument of its kind to function without the incumbrance 
of sound-proofing enclosures. 

A microscope viewing finder is built into the camera and is brought into position 
back of the photographing lens by rotating the camera case, which is mounted in a 

The monitor view-finder is rigidly secured to the side of the camera and does not 
pivot or swing. However, the image produced by it truly conforms to the image 
being photographed on the film. This feature enables the operator to work with 
the complete assurance of seeing exactly what is being recorded on the film and 
without having to guess or make allowances for such errors that arise from parallax 
and change of focus. 

The camera derives its driving power from a motor mounted on the back of the 
yoke member and drives direct to the shutter. Either synchronous or a-c. inter- 
lock motors may be used and driven at shutter speed. This type of drive assures 
an even and undisturbed rotating motion of the shutter. 

The film-moving mechanism, or the so-called camera movement, embodies ele- 
ments of absolute precision and locates each frame of the picture with registering 
pins that remain stationary during the exposure. The film is moved from frame 
to frame at a slower speed than with former cameras and with uniform accelera- 
tion, overcoming film damage and loop slap. 

The dwell time, or the period when the film is standing still and receiving the 
exposure, is long and allows for exposure with a 200-degree shutter. These fea- 
tures provide a means for producing pictures showing a superb quality of definition 
and freedom from defects. 

Many features of convenience are apparent. The camera may be synchronized 
with projection process by looking through a special aperture and turning a knob 
at the back. The camera conveniently loads when on a low or high set-up. The 
operator has an unobstructed view of the set when lining up, and may look di- 
rectly over the camera. All parts are completely sealed from the action of sand, 
dirt, and water. The camera turret mounts four lenses and provides a quick 
change from one to another. The freehead is a new hydraulic type, with adjust- 
able drag on both pan and tilt members. 



At a meeting held at the Hotel Pennsylvania on March 8th, W. B. Ray ton, of 
Bausch & Lomb Optical Company, Rochester, N. Y., presented a talk on a new 
series of projection lenses now in the course of design. The talk included a dis- 
cussion of various factors involved in projecting light from the arc to the screen 
and the necessary relations between the size of the illuminant, the reflector, and 
the lens elements. The meeting was well attended and an interesting discussion 
followed the lecture. 

The next meeting of the Section will be held at the Eastern Service Studios, 
Long Island City, N. Y., on April 6th, under the direction of R. O. Strock. 


On February 28th, at a meeting held at the Western Society of Engineers, 
Chicago, 111., A. Shapiro, of the Ampro Corporation, Chicago, presented an il- 
lustrated talk on the subject of "Motion Pictures in Education." Briefly tracing 
the history of educational pictures, the educational advantages resulting from the 
addition of sound were analyzed. The paper was illustrated by typical class- 
room pictures entitled Sound Waves and Their Sources and The Plow Breaks the 


At a recent meeting of the Admissions Committee at the General Office of the 
Society, the following applicants for membership were admitted to the Associate 


717 Hazlett St., 7635 Grand River Ave., 

Brackenridge, Penna. Detroit, Mich. 


Kodak Mexicans Ltd., T> ' a 

San Jeronimo 24, Apartado 7440, South' Norwalk, Conn. 
Mexico, D. F. 

BANTAU, A. F. J AVOR ' F - A - 

902 W. 47th St., 232 Montgomery St., 

Los Angeles, Calif. J erse y Cit y' N - J- 


556 Westfield Ave., 1245 20th Ave., 

Westfield, N. J. Longview, Wash. 



Zlota 65, 18 West Court, 

Warsaw, Poland Sausuito, Calif. 


1922 N Taft Ave , 203 Brunswlck St., 

Hollywood, Calif. Rochester, N. Y. 


NUNAN, J. K. National Carbon Co., 

8612 Third Ave., 30 East 42nd s ^ 

Inglewood, Calif. New York> N y 


1371 Walnut St., 412 W. Fifth St., 

Newton Highlands, Mass. Jamestown, N. Y. 


847 Lothrop Ave., 
Detroit, Mich. 


These films have been prepared under the supervision of the Projection 
Practice Committee of the Society of Motion Picture Engineers, and are 
designed to be used in theaters, review rooms, exchanges, laboratories, 
factories, and the like for testing the performance of projectors. 

Only complete reels, as described below, are available (no short sections 
or single frequencies). The prices given include shipping charges to all 
points within the United States; shipping charges to other countries are 

35-Mm. Visual Film 

Approximately 500 feet long, consisting of special targets with the aid 
of which travel-ghost, marginal and radial lens aberrations, definition, 
picture jump, and film weave may be detected and corrected. 

Price $37.50 each. 

16-Mm. Sound-Film 

Approximately 400 feet long, consisting of recordings of several speak- 
ing voices, piano, and orchestra; buzz-track; fixed frequencies for focus- 
ing sound optical system; fixed frequencies at constant level, for de- 
termining reproducer characteristics, frequency range, flutter, sound- 
track adjustment, 60- or 96-cycle modulation, etc. 

The recorded frequency range of the voice and music extends to 6000 
cps.; the constant-amplitude frequencies are in 11 steps from 50 cps. to 
6000 cps. 

Price $25.00 each. 

16-Mm. Visual Film 

An optical reduction of the 35-mm. visual test-film, identical as to 
contents and approximately 400 feet long. 
Price $25.00 each. 







Volume XXXII May, 1939 



A Consideration of the Screen Brightness Problem 

O. REEB 485 

A New 16-Mm. Film Developing Machine 

J. M. BLANEY 495 
Some General Characteristics of Chromium-Nickel-Iron Alloys 

as Corrosion-Resisting Materials F. L. LAQUE 505 

Absorption Limits for Interference Nodes in Rooms 

New Uses of Sound Motion Pictures in Medical Instruction . . . 

New Motion Picture Apparatus 

The Panoramic Screen Projection Equipment Used at the 
Palace of Light at the International Exposition (Paris, 1937) 


A 16-Mm. Studio Recorder R. W. BENFER 534 

A New Single-System Recording Attachment for Standard 

Cameras A. REEVES 540 

New Sound Recording Equipment 

A New Camera Timer for Time-Lapse Cinematography .... 

New Piezoelectric Devices of Interest to the Motion Picture 

Industry A. L. WILLIAMS 552 

The Copper-Sulfide Rectifier as a Source of Power for the 

Projection Arc C. A. KOTTERMAN 558 

Automatic Emergency Shutter Switch for Theater Fan and 

Light Control E. R. MORIN 568 

A New Densitometer H. NEUMANN 572 

Super 16-Mm. Sound and Picture Printer O. B. DEPUE 575 

A Film-Cement Pen R. J. FISHER 578 

Current Literature 580 

Hollywood Convention : Abstracts of Papers 582 

Society Announcements 585 





Board of Editors 
J. I. CRABTREE, Chairman 




Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1939, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 


** President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 
** Past-President: S. K. WOLF, RKO Building, New York, N. Y. 
** Executive Vice-P resident: N. Levinson, Burbank, Calif. 

* Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
** Editorial Vice-P resident: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

* Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 
** Convention Vice-President: W. C. Kunzmann, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 

* Treasurer: L. W. DAVEE, 153 Westervelt Ave., Tenafly, N. J. 

** M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

* H. GRIFFIN, 90 Gold St., New York, N. Y. 

* D. E. HYNDMAN, 350 Madison Ave., New York, N. Y. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

* A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 

** H. G. TASKER, 14065 Valley Vista Blvd., Van Nuys, Calif. 

* Term expires December 31, 1939. 
** Term expires December 31, 1940. 


O. REEB ! 

Summary. The great interest that the problem of optimal screen brightness holds 
in motion picture engineering is proved by the numerous researches on the subject in 
recent years. Besides the very interesting American papers published in this Jour- 
nal, some recent German works are worthy of consideration. 

In 1936 Zimmermann determined the dependence of the visual effect upon the screen 
brightness and found that a maximum value is attained at about 14 foot-lamberts . 
He investigated also the influence of light distribution, and temporary brightness 
changes. Finally he pointed out that the time the eye needs to see all recognizable 
contrasts varies, according to the brightness level, between 1 /s and Vio second. 

In 1936 Rieck verified, under conditions similar to those in cinema theaters, the 
character of the contrast-sensibility relation that Brodhun and Konig had found in 
their classical research. 

Very recently H. Frieser and W. Munch reported results obtained by projecting a 
detail test-object. They determined the contrast threshold function under conditions 
very similar to those of actual projection. They did not find a material increase in the 
number of distinguishable contrast steps for picture brightnesses exceeding 10 foot- 

It is to be hoped that the consideration of the results of all these investigations will 
form a basis for early temporary screen brightness standardization. 

The numerous investigations, reports, and discussions on the prob- 
lem of screen brightness that have been published in the JOURNAL 
within recent years indicate the great interest which the study of this 
question has aroused in America. 

Since the differences of screen brightness in the various theaters 
are large and the average brightness level is comparatively small, it is 
difficult for the industry to make prints suitable for all theaters. 
For that reason there is also in Germany a desire to arrive at a screen 
brightness standard that would make for the best possible uniformity 
of screen illumination. During recent years, three important in- 
vestigations have been made in Germany to clear up these questions. 

* Presented at the 1938 Spring Meeting at Washington, D. C.; received 
April 14, 1938. 

** Osram G. m. b. H., Berlin, Germany. 




[J. S. M. P. E. 

In 1936 K. F. Zimmermann 1 published the results of an investiga- 
tion which had been carried out in the Illuminating Engineering 
Laboratory of the Osram Company. In this investigation he deter- 
mined experimentally the contrast sensitivity of the eye under 
conditions very similar to those found in motion picture projection. 
In order to be able to determine the contrast sensitivity not only for 
contrast thresholds but also for the greater contrasts which are ob- 
served more frequently when pictures are projected on a screen, he 
chose as a criterion the time of observation necessary to recognize 
a certain contrast. Fig. 1 shows a projection field of the same kind 
as used in his experiments. The field is divided into four equal parts. 
Near the center a small circular test-contrast area was projected 
alternately into one of the four quadrants, the time of exposure being 

changed each time. The observer was 
required to indicate whether he had 
seen the test circle, and if so, in which 
quadrant. The brightness of the adap- 
tation field was varied between approxi- 
mately 0.5 and 14 foot-lamberts,* while 
the brightness of the small contrast field 
projected upon the adaptation field was 
varied between about 5 and 33 foot- 
lamberts. The sizes** of the screens 
used were 13, 19, or 26 degrees and the 
size of the contrast field was 1 1 minutes. 
Of the results of this work only the most important will be de- 
scribed here : 

(1) If the ratio of the brightness being projected in the small test- 
field in relation to the brightness of the total area is designated as 
contrast, it is shown that the product of contrast and required time of 
observation remains constant with constant adaptation brightness. 
In other words, at a certain adaptation brightness, the stimulus time 
necessary to recognize a certain contrast is in inverse proportion to 

FIG. 1. Test-field used by 

* Brightness values are here given in foot-lamberts. In the German reports 
the unit apostilb (abbr. asb.) is used. 10 asb. = 1 millilambert = 0.93 foot-lam- 

The question of which unit would be most suitable for use in international 
standardization is not discussed here, as neither the foot-lambert nor the apostilb 
is accepted as an international unit. 

** 7. e., the angle of the projected beam (Ed.). 

May, 1939] 



the test contrast. Zimmermann defines the reciprocal value of this 
product as Sehleislung, an expression which may be translated as 
"visual effect." Hence, the larger the visual effect, the shorter the 
time required for the eye to recognize a certain contrast, and the 
smaller the contrasts recognized within a certain time. Further- 
more, the visual effect is constant for a definite adaptation brightness. 
(2) The dependence of the visual effect upon the adaptation 
brightness as found by Zimmermann is shown in Fig. 2. Curves 1, 2, 
and 3 correspond to three different screen sizes (13, 19, and 26). 
Accordingly, the visual effect increases very rapidly in the lower 
adaptation brightness ranges, and at the higher brightness ranges, the 


SO 100 750 


FIG. 2. Dependence of visual effect upon adapta- 
tion brightness. Image size: (1} 26, (2) 19, 
(3) 13. 

increase is very slow. At a screen size of 26, a maximum visual 
effect is reached with a picture brightness of 14 foot-lamberts. At 
brightnesses of over approximately 7.5 foot-lamberts, no considerable 
increase of visual effect is reached with larger areas. 

(3) In some experiments, in order to examine the influence of 
brightness distribution in the screen area, Zimmermann replaced the 
uniformly lighted screen with a checkered field (Fig. 3) and varied 
the brightness of the central field and of the checkered field in different 
combinations. All these experiments proved clearly that for the at- 
tained visual effect only the central brightness of the screen is im- 

(4) In a further series of experiments Zimmermann investigated 
the influence of a temporary change of the adaptation brightness as it 

488 O. REEB [j. s. M. P. E. 

occurs with the change from a light scene to a dark one and vice versa. 
A temporary brightness contrast of 1 : 2.6 did not influence the mea- 
sured visual effect, while temporary contrasts of 1 : 20 or 23 : 1 re- 
sulted in a decrease of the visual effect of about 1 1 per cent. 

(5) An investigation to determine whether, at the same bright- 
ness, screen areas of different sizes would cause different brightness 
impressions on the eye of the observer, did not give any definite 
proof of such an effect at screen sizes of 8 and 26. 

(6) From the constancy of the product contrast X stimulus time 
it was concluded that, at the adaptation brightness concerned, the 
greatest stimulus time belongs to the smallest contrast perceivable, 

FIG. 3. Checkered test-field used by 

i. e., the threshold contrast. This maximum stimulus time is conse- 
quently the time needed by the eye for the perception of all contrasts 
recognizable at all with the special adaptation brightness used in this 
case. The dependence of this maximum stimulus time upon the 
adaptation brightness is shown in Fig. 4. This maximum stimulus 
time has a value of about 0.1 second at high brightnesses (10 to 14 
foot-lamberts) ; while maximum stimulus times of about 0.2 to 0.3 
second are necessary at lower brightnesses which correspond to 
shadow details in the picture. Incidentally, Zimmermann's results 
are based upon 42,000 observations gathered from eleven observers. 
The classical researches of Konig-Brodhun on the contrast sensi- 
tivity of the eye in relation to the adaptation brightness were com- 
pleted in 1936 with an investigation by Rieck 2 in the Beleuchtungs- 

May, 1939] 



technisches Institut der Technischen Hochschule Berlin. Rieck 
determined the contrast threshold up to a field brightness of about 185 

so too 


FIG. 4. 

Dependence of maximum stimulus time upon 
adaptation brightness. 

foot-lamberts for a screen of 20 and a test-field of 2. The system- 
atic course of his curves (Fig. 5) agrees with the values of Konig- 
Brodhun obtained with an adaptation field of 6 and a test-field of 3. 

5 70 50 700 


FIG. 5. Dependence of contrast threshold upon 
adaptation brightness. Surrounding field brightness 
(a) =0; (6) = image field brightness; (c) = image 
field brightness; (d) = sensitivity difference according 
to Konig-Brodhun. Curves a, b, and c from measure- 
ments by Rieck. 

The absolute values are a little higher with the larger area used in 
Rieck's investigations. A change in the brightness of the surround- 
ing field results, according to Rieck's investigations, in an increase of 



[J. S. M. P. E. 

the contrast sensitivity, until the brightness of the surrounding field 
is equal to the brightness of the screen area. 

This statement, that the best contrast sensitivity is to be attained 
with a very bright surrounding field, seems to be in opposition to the 
work of O'Brien and Tuttle, who demonstrated that only very low 
brightnesses of the surrounding field are considered as not being dis- 
turbing to the spectator. However, comparison of these two results 
is very difficult, because it is not known which average brightness of 
the projected picture of O'Brien and Tuttle's experiments should be 
compared with Rieck's adaptation brightness values. 

Frieser and Munch 3 investigated the visual 
conditions in a projected picture, thus ap- 
proaching more closely to the conditions 
found in actual practice than did former 
experimenters. These investigations were 
carried out in the Wissenschaftlich-Photo- 
graphisches Institut of the Dresden Tech- 
nische Hochschule and have been published 
only very recently. For their purpose Frieser 
and Munch used a so-called detail-plate, 
following the example of Goldberg and 
Luther. This in effect consisted of two 
crossed neutral gray wedges. One gray 
wedge extending uniformly over the whole 
field was combined with a plate provided 
with detailed stripes, its gradation of bright- 
ness being at right angles to that of the gray wedge. This forms the 
complete detail-plate shown in Fig. 6. Such a detail-plate makes it 
possible to determine, in a single screen area, the dependence of the 
contrast threshold upon the adaptation brightness which is variable 
between wide limits by means of the gray wedge. A detail-plate was 
projected by Frieser and Munch into a normally projected picture, as 
shown in Fig. 7. The different observers explored the picture to 
determine the just-recognizable contrasts. The results were re- 
corded on a sheet of paper by an automatic device. Fig. 8 shows 
curves obtained by one observer. 

Fig. 9 shows the dependence of the contrast sensitivity upon the 
brightness for different maximum brightnesses of the projected pic- 
ture. Every curve corresponds to a special maximum brightness of 
the picture and of the detail-plate. It is evident that at lower maxi- 

FIG. 6. Detail-plate 
used by Frieser and 

May, 1939] 



mal brightnesses there is a greater contrast sensitivity for lower 
brightness details than at higher maximum brightnesses. At higher 
brightness this proportion reverses, probably due to glare. 

Further investigations of the authors refer to the dependence of the 
curves obtained of the contrast sensitivity upon the character, the 
brightness, and the size of the projected picture, and upon the in- 
fluence of the change of adaptation when entering the projection 
room. From these results will be pointed out only the fact that no 

FIG. 7. 

Example of test-picture used by Frieser and 

influence of the contrast sensitivity was noticed with a change in the 
screen size from 23 to 63. 

Finally (Fig. 10), the number of brightness steps distinguishable in 
a picture and the course of the visual acuity, as charted, is dependent 
upon the maximum brightness. It can be seen, as observed by Luck- 
iesh, that the maximum value of the visual acuity is already attained 
with very low brightnesses. Also, the number of recognizable bright- 
ness thresholds increases very quickly at first, but there is no consider- 
able increase with brightnesses of more than about 10 foot-lamberts. 

A comparison of the results given by these three investigations 
shows the following : 



[J. S. M. P. E. 

Zimmermann's measurements of the visual effect and Rieck's 
values of the contrast threshold agree very well, although the methods 
used are very different. They both found that an optimum value of 

FIG. 8. Example of test-sheet obtained by 
one observer in Frieser and Miinch's investi- 

visual conditions is attained with about 14 foot-lamberts, and that the 
visual effect corresponding to 8 foot-lamberts is not essentially sur- 
passed by a further increase of the adaptation brightness. In these 


togB -/ 1 2 J 

B 0,1 1 1Q 100 1000 asb 

FIG. 9. Dependence of contrast sensitivity upon brightness. 

researches the question is not answered as to which brightness value 
of various brightnesses existing in a really projected picture corre- 
sponds to the "adaptation brightness" of these experiments. This 

May, 1939] 



problem is solved to a large degree by the investigations of Frieser 
and Munch. These authors found a curve showing the relation be- 
tween the number of recognizable contrast thresholds and maximum 
picture brightness, whose character is very similar to those of Zim- 
mermann's and Rieck's curves. Thus, Frieser and Munch conclude, 
also, that a minimum brightness of about 8 foot-lamberts with run- 
ning shutter and no film in the gate is sufficient to guarantee good pic- 
ture projection. Although they found a slight increase of picture 
quality with still higher brightness levels, they believe that values of 
more than 8 foot-lamberts in the lightest parts of the picture, which 






*^*""'^ Threskolrf volwa 




Visual acuify 





SO 100 200 B atax - 300 asb 



FIG. 10. Number of brightness steps and visual acuity 
as dependent upon maximum brightness. 

corresponds to about 16 foot-lamberts without film, would not be so 
satisfactory on account of the possibility of flicker. 

Between the results of the reported German researches and those 
of the SMPE Projection Screen Brightness Committee there is a large 
degree of similarity. This agreement seems surprisingly good with 
regard to the very different methods and conditions used by Lowry, 
O'Brien and Tuttle, Wolf, Luckiesh and Moss, and other American 

A discussion of the German researches by the experts of the 
"Deutsche Kinotechnische Gesellschaft" showed that there is a 
possibility of arriving at a standard of screen brightness in the not too 
distant future. The German experts believe it best to recommend a 
brightness value that can be attained in all theaters, even the largest. 

494 O. REEB 

This is the reason why the difference from 7 foot-lamberts for the low 
value to 14 foot-lamberts for the high value seems too great. We in 
Germany would prefer a brightness standard of 8 foot-lamberts, 
which could be followed by all theaters, instead of a higher standard, 
which would furnish only a slightly better visual effect and would not 
be attainable by all theaters. 

Moreover, screen brightness standardization should be completed 
by a recommendation limiting the brightness losses that occur both 
at the border of the screen and by viewing the screen under the largest 
observation angle possible in the individual theater. This latter 
limit is necessary in regard to the screens of the directional type. A 
brightness loss of 25 per cent measured horizontally from the center to 
the screen border and a loss of 50 per cent for viewing at the most un- 
favorable angle to the screen seem to be admissible. 

We feel that it would be very desirable to make brightness measure- 
ments, as promptly as possible, in a number of motion picture thea- 
ters, under different conditions at the center of the screen, at the 
border, and with different viewing angles. We intend to start such 
measurements in Germany in the near future, and feel that it would 
be another step toward the desired goal of standardization if also in 
America more such data could be obtained. A survey of such data 
would provide a very good basis for discussion at next year's meeting 
of the International Commission on Illumination. There we might 
aspire to international agreement, which is requisite for uniformly 
good projection of the films in the various countries. I am exceed- 
ingly glad to have had the opportunity of speaking here on these 
problems, especially since the preparation of the screen brightness 
discussion for the 1939 ICI meeting lies in the hands of the American 


1 ZIMMERMANN, K. F. i "Lichttechnische Untersuchunger iiber Lichtbildprojeck- 
tion," Das Licht (1936), pp. 78, 98, 115, 138. 

2 RIECK: Das Licht (Dec., 1936), p. 246. 

3 FRIESER AND MUNCH: Die Kinotechnik (April, 1938). 



Summary. A 16-mm. developing machine designed for installation in loft 
buildings without disturbing overhead ducts and piping is described. The machine 
is rated at 150 feet per minute. A detailed description is given of the constructional 
features of the equipment and its control. 

The 16-mm. developing machine described here is designed for in- 
stallation in loft buildings without disturbing overhead ducts and 
piping. It is 20 feet long by 28 inches wide, and stands 74 inches high, 
exclusive of air ducts which may enter from either the top or the 
bottom of the dryer (Fig. 1). 

The machine is rated at 150 feet per minute and, at that speed, 
development is effected in 3 1 /z minutes, fixing in 3 x /2 minutes, and 
washing in 7 minutes. The minimum drying period is 16 minutes, 
thus providing for low- temperature drying and, consequently, im- 
provement in sound and picture quality. 

There are two main drive shafts without couplings mounted in 
tandem on a structural steel frame which is normalized and accu- 
rately machined. These shafts are coup