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Full text of "Electric incandescent lighting"

BY THE SAME AUTHORS 

Elementary Electro -Technical Series 

COMPRISING 

Alternating Electric Currents. 
Electric Heating. 

Electromagnetism. 

Electricity in Electro-Therapeutics. 

Electric Arc Lighting. 
Electric Incandescent Lighting. 
Electric Motors. 

Electric Street Railways. 
Electric Telephony. 

Electric Telegraphy. 

Cloth, Price per Volume, $1.00. 



Electro-Dynamic Machinery. 
Cloth, $2.50. 



THE W. J. JOHNSTON COMPANY 

253 BROADWAY, NEW YORK 



ELEMENTARY ELEOTKO-TECHNICAL SERIES 

.ELECTRIC 
INCANDESCENT LIGHTING 



BY 

EDWIN J. HOUSTON, PH. D. 



\\ 

AND 



A. E. KENNELLY, Sc. D. 



NEW YORK 

THE W. J. JOHNSTON COMPANY 

253 BROADWAY 

1896 




COPYRIGHT, 1896, BY 
THE W. J. JOHNSTON COMPANY. 



PREFACE. 

THIS little volume has been prepared by 
the authors with the view of presenting 
both the art and science of practical electric 
incandescent lighting to the general public, 
in such a manner as shall render it capable 
of being understood without any previous 
technical training. 

The necessity of some general knowl- 
edge of the principles underlying the prac- 
tical applications of incandescent lighting, 
will be appreciated from the fact that at 
the present time incandescent lamps are 
manufactured in the United States at a 
rate of about eight millions per annum. 
This of course represents a large amount 

iii 



iv PREFACE. 

of invested capital, only a small portion of 
which is engaged in the actual manufacture 
of the lamps, by far the greater part being 
invested in the central stations where the 
electric current is generated, and in the 
streets and buildings where the conductors 
and fixtures are provided. Since the whole 
of this important industry has practically 
come into existence since 1881, compara- 
tively little opportunity has been afforded 
to the public of acquiring a fair under- 
standing of the subject. 

It is in the hope of meeting the above 
want that the authors have written this 
book. 

PHILADELPHIA, 

June 1, 1896. 



CONTENTS. 



I. ARTIFICIAL ILLUMINATION, 1 

II. EARLY HISTORY OP INCANDESCENT 

LIGHTING, . . . . .18 

III. ELEMENTARY ELECTRICAL PRINCIPLES, 43 

IV. PHYSICS OF THE INCANDESCENT ELEC- 

TRIC LAMP, ... .65 

V. MANUFACTURE OF INCANDESCENT 
LAMPS. PREPARATION AND CAR- 
BONIZATION OF THE FILAMENT, . 83 
VI. MOUNTING AND TREATMENT OF FILA- 
MENTS, ...... 99 

VII. SEALING-IN AND EXHAUSTION, . .118 
VIII. LAMP FITTINGS, . . . .135 

IX. THE INCANDESCENT LAMP, . .163 

X. LIGHT AND ILLUMINATION, . .198 

XI. SYSTEMS OF LAMP DISTRIBUTION, . 210 

XII. HOUSE FIXTURES AND WIRING, . 237 



Vi CONTENTS. 

CHAPTER PAGE 

XIII. STREET MAINS, .... 284 

XIV. CENTRAL STATIONS, . . .304 
XV. ISOLATED PLANTS, . . . .324 

XVI. METERS, 334 

XVII. STORAGE BATTERIES, . . .345 
XVIII. SERIES INCANDESCENT LIGHTING, . 374 
XIX. ALTERNATING - CURRENT CIRCUIT 

INCANDESCENT LIGHTING, . .386 
XX. MISCELLANEOUS APPLICATIONS OF 

INCANDESCENT LAMPS, . . 402 
INDEX, 419 



ELECTRIC INCANDESCENT 
LIGHTING. 

CHAPTER I. 

AETIFICIAL ILLUMINATION. 

t 

DOUBTLESS, the earliest artificial illumi- 
nant employed by primitive man was the 
blazing fagot, seized from the fire. The 
step from this to the oil lamp marked an 
era in civilization, since man's work was 
then not necessarily limited in time by the 
rising and setting of the sun. It is diffi- 
cult, at this time, to estimate properly the 
great boon to civilization this invention 
afforded. Although at first sight it does 
not seem to be a very great step from the 



2 ELECTRIC INCANDESCENT LIGHTING. 

flickering light of the torch to that of the 
oil lamp, yet, when we consider the re- 
quirements of an artificial illuminant, the 
superiority of the latter is evident in what 
may, perhaps, be regarded as the most essen- 
tial requirement of such an illuminant ; 
namely, its duration; i. e., the length of 
time during which it can supply a 
proper illumination without renewal. In- 
stead of the fitful flickering of the torch 
we have the comparatively steady glow 
of the oil lamp ; instead of the evanescent 
light of the torch, we have in the oil 
lamp a means for furnishing light for 
many hours. 

Fortunately, for the sake of progress, 
man's ingenuity was not arrested by this 
great achievement. There followed in its 
wake, various improvements in forms of 
oil lamps, but this illumiuant sufficed to 



ARTIFICIAL ILLUMINATION. 3 

light the world for many centuries, as the 
tombs, parchments and bas reliefs of the 
remote past attest. 

Passing by the many improvements in 
various forms of oil lamps, perhaps the 
next noted step in the production of arti- 
ficial light followed in the discovery of 
coal oil, and marked improvements were 
made in lamps designed especially to burn 
this natural illuminant. The next great 
improvement in this direction was the 
lighting of extended areas by means of 
illuminating gas. Here, for the first time 
in the history of the art, means were de- 
vised for supplying an illuminant from a 
central station, under circumstances which 
permitted of its ready distribution over 
extended areas. 

The greatest step, however, in the pro- 



4 ELECTRIC INCANDESCENT LIGHTING. 

duction of an artificial illuminant was un- 
doubtedly that which followed the inven- 
tion of the voltaic pile in 1796. Then, for 
the first time in the history of science, 
means were provided whereby powerful 
electric currents could be readily produced 
and their effects observed. Naturally the 
use of these currents soon led to the dis- 
covery of the very powerful illuminating 
properties possessed by the voltaic arc. 
It must not be supposed, however, that in 
these successive steps each new illuminant 
completely supplanted its predecessors. 
On the contrary, the very fact that night 
could thus be transformed into day, stimu- 
lated improvements in the pre-existing 
forms of illuminants, and, in the emulation 
thus produced, marked advances were 
made in earlier methods. Thus, it was at 
one time claimed, when gas was first intro- 
duced into cities, that existing methods of 




lighting would sot^ entirely repla^ 
by the new illummany'foj^ 
being the case, old methods were suffi- 
ciently improved to fairly hold their own, 
and even to require continued improve- 
ments in the new illuminant, in order to 
maintain its superiority. So, again, when 
the electric light was introduced, it was 
predicted, by enthusiasts that gas lighting 
would now be entirely replaced by its new 
rival, but, as is well known, this expec- 
tation was not realized. So markedly have 
improvements in different methods of 
illumination gone hand in hand, that we 
possess to-day all our original methods, 
save, perhaps, the torch. 

Before discussing the advantages pos- 
sessed by the incandescent electric light, it 
will be advantageous to consider in general 
the requirements of any artificial illumi- 



6 ELECTRIC INCANDESCENT LIGHTING. 

nant. It is evident that the most satis- 
factory artificial illuminant will be that 
whose properties most nearly resemble 
those of the sunlight it replaces. No 
existing illuminant completely satisfies 
our requirements from this standpoint. 
The ideal artificial illuminant should 
possess the following properties ; it should 
be, 

(1) Safe. 

(2) Cheap. 

(3) Hygienic. 

(4) Steady. 

(5) Eeliable. 

(6) Akin to sunlight in color. 

(7) Capable of ready subdivision. 

(8) Cool. 

(9) Readily turned on and off at a 
distance. 

(10) Amenable to the purposes of dec- 
oration. 



ARTIFICIAL ILLUMINATION. 7 

As regards safety, it is evident that an 
artificial illuminant should be safe both 
to property and to life. All bare or naked 
flames are open to the objection that com- 
bustible material, coming in contact with 
them, may start dangerous conflagrations. 

A good artificial illuminant must neces- 
sarily be cheap; for, unless it can be fur- 
nished a"t a price which brings it fairly 
within the reach of all, its use will be 
very limited. 

All artificial illuminants must necessarily 
permit of continued use without any dele- 
terious eifects on the health. Such defects 
may arise either from products of combus- 
tion vitiating the surrounding air, or, possi- 
bly, in extreme cases, from injury to sight. 

Steadiness is a prime essential of a good 



8 ELECTKIC INCANDESCENT LIGHTING. 

illuminant. If an artificial light produces 
an unsteady, nickering illumination, an 
injurious strain may be put on the eye, in 
its endeavor to accommodate itself to the 
varying intensity of illumination. More- 
over, a good artificial illuminant must be 
reliable. In other words, it must be able 
to furnish light without constant attention, 
and without danger of becoming acciden- 
tally extinguished. 

Ordinary sunlight, as is well known, con- 
sists of a mixture of a great variety of 
colors. The color of natural bodies is 
entirely due to the light which falls on 
them. For example, a green leaf, illumined 
by sunshine, possesses the power of absorb- 
ing nearly all the sunlight but the green 
light, which it gives off. For such a green 
leaf to appear of its natural color by arti- 
ficial light, this light must possess not only 



ARTIFICIAL ILLUMINATION. 9 

the exact tints of the various greens which 
it throws off in sunlight, but also the 
various proportions of such tints. The 
same is true for other colors. A good 
artificial illuminant, therefore, to be able 
to replace sunlight, should possess not only 
all the colors of the sunlight, but should 
also possess these colors in nearly the same 
relative intensities as does sunlight. 

A requirement of an artificial illum- 
inant, which is very difficult to fulfil, is 
that the light it produces shall not be 
localized, but shall uniformly illumine the 
spaces to be lighted. In order to meet 
this requirement, the artificial illuminant 
must readily yield itself to subdivision, 
that is, instead of giving a great amount of 
light at each of a few points, it should 
give a smaller 'quantity of light at a great 
number of separate points. 



10 ELECTRIC INCANDESCENT LIGHTING. 

The light of all artificial illmninants 
is accompanied by heat, and, in nearly every 
case, the amount of heat so accompany- 
ing the light is very greatly in excess of 
what is essentially necessary. Such is 
true even in the case of sunlight. A nota- 
ble exception, however, is found in the 
phosphorescent light of the firefly and the 
glow-worm, which yield light practically 
devoid of wasteful heat ; i. e., non-luminous 

Iwat. 



Another requirement of an artificial 
illuminant is that it shall readily yield 
itself to control, that is to say, that it shall 
easily be turned on or off at a distance, 
otherwise, the location of the separate 
sources of light would necessarily be 
limited and thus prevent the most advan- 
tageous distribution. Finally, a good arti- 
ficial illuminant should be readily adapta- 



ARTIFICIAL ILLUMINATION. 11 

ble to the purposes of decoration, or 
it will otherwise be shorn of many of its 
advantages. 

The principal artificial illuminants in 
use at the present day, are, coal oils, gas, 
candles, arc and incandescent electric 

lamps. 

t 

The incandescent lamp is now so 
generally employed as an indoor artificial 
illuminant, and its advantages for this 
purpose are so evident, that it is scarcely 
necessary to show how much more fully it 
meets the requirements of a good illuinin- 
ant than any of its predecessors. It suffices 
to say that it does not vitiate the air, is re- 
liable, steady, can be maintained without 
any trouble on the part of the consumer, 
and readily yields itself both to sub-division 
and to decorative effects. When used on 



12 ELECTRIC INCANDESCENT LIGHTING. 

a comparatively large scale it can compete 
favorably as regards cost witli any other 
artificial illuininant, and, even when em- 
ployed on a small scale, its manifold advan- 
tages will frequently more than compensate 
for the disadvantage of a slightly increased 
cost. 

As regards the ability of an incandes- 
cent lamp to produce a color of light akin 
to sunshine, it must be confessed that it is 
far from realizing this object, but this 
objection also exists to even a greater 
degree in nearly all other artificial illu- 
minants. Coal oil, candles, gas, and oil 
lamps generally, do not produce a light so 
nearly akin to sunshine, as does the incan- 
descent lamp. As we shall see later on 
the light emitted by an incandescent lamp 
can be made to approach more closely the 
characteristics of sunlight by increasing 



ARTIFICIAL ILLUMINATION. 13 

the temperature of the glowing carbon 
filament. 

When the incandescent electric light 
was first introduced on a commercial scale, 
a belief existed that the extended intro- 
duction of this illuminant would be 
attended by many dangers, and it is true 
that, when negligently installed, such 
dangers do exist, but experience has amply 
proved that when installed with ordinary 
care, there is far less danger from the use 
of incandescent lighting than from the use 
of any other artificial illuminant. 

So far as the safety of incandescent 
lighting for fire risk is concerned, a re- 
port of the Massachusetts Insurance Com- 
missioner, giving data extending from 1884 
to 1889, as to the origin of 12,935 confla- 
grations which took place in Massachusetts 



14 ELECTRIC INCANDESCENT LIGHTING. 

during that time, will speak favorably for 
this illuminant. Of this number of fires 
only 42 were attributed to electric wires. 
The breakage and explosion of kerosene 
oil lamps produced in the same time about 
22 times as many fires, while the careless 
use of matches produced more than 10 
times as many. 

As to the danger to life, the evidence is 
still more in favor of electricity as an arti- 
ficial illuminant. While it is true that 
fatal accidents do occur from contact with 
high-pressure wires, yet the proper instal- 
lation of a system practically precludes the 
possibility of such accidents. Besides the 
immunity from fire which the electric 
lamp ensures, owing to the fact that the 
filament is sealed in a glass chamber, thus 
preventing contact with combustibles, it 
also possesses the marked advantage that 



ARTIFICIA 




it dispenses entire! ; 
dangerous friction matched 
readily capable of being lighted and ex- 
tinguished at a distance by the mere turn- 
ing of a switch. To thoroughly appreciate 
the danger to life from electricity, and to 
ascertain the extent to which it can be 
avoided, it will be necessary to understand 
some of the leading elementary principles 
of electrical science, and we will, there- 
fore, postpone this consideration to a later 
chapter. 

An extended experience with the incan- 
descent lamp, has clearly established its 
advantages over gas or coal oil. Take, for 
example, convenience of night work, in a 
large textile manufactory. It is a well 
known fact that the air of such buildings, 
when illumined by gas, so rapidly heats and 
becomes so rapidly vitiated during summer 



16 ELECTRIC INCANDESCENT LIGHTING. 

time, that the amount and character of the 
work the workmen are capable of per- 
forming, necessarily suffers as compared 
with day work. Since the introduction of 
the incandescent lamp, however, the ab- 
sence of increase of temperature and 
impure air, on prolonged runs, is so marked, 
that in many instances it has been found 
that the amount and character of the night 
work compares very favorably with day 
work during the summer season. This 
circumstance has frequently occasioned 
surprise to the public, since the tempera- 
ture of the glowing filament in an incan- 
descent lamp is quite high, but it must be 
remembered that while an incandescent 
lamps emits no gas, the filament not being 
con sinned, a gas burner not only gives off 
all the gas that would escape from it were 
it unlighted, but, in addition, a much 
greater volume of heated air. Every cubic 



ARTIFICIAL ILLUMINATION. 17 

foot of ordinary illuminating gas requires 
for its combustion, the oxygen from about 
20 cubic feet of air, so that a burner con- 
suming 5 cubic feet per hour combines with 
the oxygen of about 100 cubic feet of air 
per hour. Besides vitiating such air by 
the products of combustion, and raising its 
temperature by the great amount of heat 
given off, this vitiation and increase of 
temperature requires much more thorough 
ventilation than when the incandescent 
lamp is employed. In cases where the 
character of night work requires keen 
sight, a highly heated vitiated air has an 
injurious influence upon the eye. 



CHAPTER II. 

EARLY HISTORY OF INCANDESCENT LIGHTING. 

ELECTRICITY was first employed as an 
illuminant in the arc lamp. In this lamp, 
as is well known, two rods of carbon are 
first brought into contact, and then gradu- 
ally separated while a powerful electric 
current is passing between them. A 
cloud of incandescent carbon vapor, called 
the voltaic arc is thus established, and the 
ends of the carbons, particularly that of 
the positive carbon, or the one from which 
the current flows, becomes intensely 
heated, forming a brilliant source of light. 

The greatest difficulty attending the 
practical application of the arc system of 

18 



EARLY HISTORY. 19 

lighting, arose from the fact that the arc 
lamp was too intense a source of light for 
most practical purposes within doors, and 
could not readily be subdivided into a 
number of smaller units ; for, even if the 
space to be lighted would require all the 
light emitted by a single arc lamp, yet 
this light, coming from practically a single 
point, would necessitate the production of 
disagreeable shadows. 

From very early times in the history of 
the application of electricity to lighting, 
the idea was conceived by various invent- 
ors of employing continuous conductors, 
instead of the discontinuous conductors in 
arc lighting. These continuous conductors 
were rendered incandescent by the pas- 
sage through them of an electric current ; 
or, in other words, the current heated 
them to a white heat. Various substances 



20 ELECTRIC INCANDESCENT LIGHTING. 

were employed for this purpose, at first in 
air, such as platinum or iridium wires, or 
other metals. These lamps, however, were 
not found to give practically useful 
results, since if the current strength was 
made sufficiently great to raise them to 
a white heat, although the light they 
would then emit would be quite satisfac- 
tory, yet disintegration would occur, from 
the free contact of the air, and would soon 
result in the destruction of the lamp. 
Moreover, the temperature at which the 
glowing wire becomes white hot, is so 
very nearly the temperature of its melting 
point, that any accidental increase in the 
-current, even to a slight degree, would 
result in the fusion of the wire and the 
rupture of the lamp. If to avoid these 
difficulties, the lamp was burned at a 
lower temperature, the light it emitted 
was unsatisfactory, not only on account of 



EARLY HISTORY. 21 

its lessened intensity, but also because it 
was distinctly red and dull. 

During the year 1878, a great improve- 
ment was effected in the platinum incan- 
descent lamp, whereby platinum was ob- 
tained in a condition in which it was 
possible to employ safely much greater 
current strength without rapid deteriora- 
tion. This process consisted essentially in 
sending a gradually increasing current of 
electricity through the wire while in a 
vacuous space. As is well known, plati- 
num possesses in common with some 
other metals, the power, of absorbing or 
occluding within its mass, air or other 
gases. When such a wire is heated by the 
sudden passage of an electric current, this 
occluded gas is liberated explosively, and 
the wire thereby becomes cracked, fissured, 
and rapidly disintegrates. It was dis- 



22 ELECTRIC INCANDESCENT LIGHTING. 

covered that if the wire, while in a vacuous 
space, was subjected to the passage of a 
gradually increasing current of electricity, 
first beginning with a weak current, that 
the occluded gas was slowly liberated and 
that if, when a very high vacuum was ob- 
tained, the wire was maintained for a few 
moments at a temperature only a little 
below that of its melting point, it became 
physically changed, free from cracks and 
had its point of fusion raised. Moreover, 
the surface of the wire was altered, so that 
a given current strength produced a greater 
amount of light. The invention of a lamp 
consisting of such a treated platinum wire 
in a vacuous space was a marked step in 
the production of an artificial electric illu- 
niinant. Nevertheless, even the improved 
conductor did not answer commercial re- 
quirements, so that the improved platinum 
lamp did not come into any extended use. 



EARLY HISTORY. 23 

To make the incandescent lamp practi- 
cable it was necessary to enclose the wire 
in a transparent chamber from which the 
air had been removed. Such an improve- 
ment would render the lamp more efficient 
for the following reasons : 

(1) The absence of air would prevent 
the rapid disintegration of the wire. 

(2) The absence of air would prevent 
the re-absorption or occlusion of air by the 
heated wire. 

(3) The absence of air would prevent 
loss of heat, and much electric power would 
thereby be saved since a smaller current 
would bring the wire to the incandescent 
temperature. 

(4) The absence of drafts of air would pre- 
vent irregular coolings and heatings of the 
wire, with consequent fluctuations of light. 

(5). The wire would be protected from 
mechanical injury. 



24 ELECTRIC INCANDESCENT LIGHTING. 

The early history of the art contains the 
names of numerous inventors who applied 
the foregoing principles for the purpose of 
producing satisfactory incandescent lamps. 
Without attempting to record in full all 
these early attempts, we will briefly allude 
to some of the more prominent of the early 
inventors in this field of artificial illumina- 
tion. 

In 1841, Frederick De Moleyn patented 
in England a process for the production of 
an incandescent lamp, based on the incan- 
descence of platinum wire placed inside an 
enclosing glass chamber from which the 
air had been exhausted. 

In 1849 Petrie produced an incandes- 
cent lamp in which short thin rods of 
indium, or its alloys, were used as the in- 
candescent material. 



EARLY HISTORY. 25 

Considerable excitement was created in 
scientific circles in France, in 1858, by the 
announcement to the French Academy of 
Sciences by one of its members, of an 
improvement in incandescent lamps made 
by one De Changy. De Changy employed 
an incandescent platinum lamp of the form 
shown in Fig. 1, in which a wire of plati- 
num G ', is heated to incandescence by the 
passage of the current through it. The 
wire was enclosed in an exhausted glass 
vessel. The excitement caused by this 
lamp was due to the claim made by De 
Changy that he had solved the problem for 
the successful sub-division of the electric 
light. His lamp never came into com- 
mercial use. 

The great improvement in lamps of this 
type was made by the substitution of 
carbon wires for platinum wires. The 



26 ELECTRIC INCANDESCENT LIGHTING. 





FIG. 1. DE CHANGY'S LAMP. 

honor of this discovery appears to be due 
to an American by the name of J. W. 
Starr, who employed plates of carbon 



EARLY HISTORY. 27 

placed inside a glass vessel containing a 
Toricellian vacuum. Starr associated him- 
self with an Englishman of the name of 
King, and an English patent was obtained 
under the name of King. It is from this 
fact that the Starr lamp is not infrequently 
alluded to in literature as the King lamp, 
or sometimes, as the Starr-King lamp. 
Starr gave a successful demonstration in 
England with a candelabra of 26 of his 
lamps, the number of States then in the 
American Union. His untimely death, 
while on his return voyage to this coun- 
try, retarded the progress of this inven- 
tion. The Starr-King lamp is illustrated 
in Fig. 2, where A, is a rod of carbon 
clamped at its extremities to the rods G and 
J9, and situated in a Torricellian vacuum 
above the surface of mercury in a barometer 
tube, the current passed through the rod A 
raising it to the incandescent temperature. 



28 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 2. STARR-KING LAMP. 

The next invention worthy of notice 
was that of Lodygnine, who produced a 
carbon incandescent lamp in 1873. This 
invention was deemed by the St. Peters- 



EARLY HISTORY. 29 

burg Academy of Sciences, of sufficient 
merit to warrant the award of a special 
prize. Lodyguine's lamp used needles 
of retort carbon terminating in blocks 
and placed inside an exhausted glass 
globe. In practice, in order to avoid the 
expense of exhausting the globe, Lody- 
guine sometimes left air within the globe 
and then sealed it hermetically, depending 
on the consumption of the residual air 
by the heated carbons to produce a space 
devoid of oxygen. This form of vacuum, 
however, was not found suitable for com- 
mercial purposes. Lodyguine's lamp was 
improved by Kosloff, who introduced 
modifications for the supports of the 
carbon pencils. 

In 1875, Konn produced a lamp very 
similar to Lodyguine's. Konn's lamp is 
shown in Fig. 3. The glass globe J3, 



30 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 3. KONN'S LAMP. 



EARLY HISTORY. 31 

closed at the top, rests with its base upon 
a washer of soft rubber placed in the lamp 
base, and pressure is brought by the screw 
block Z, in such a manner as to maintain 
an air-tight joint. The lamp was ex- 
hausted through the orifice K. The 
metallic base formed one terminal of the 
lamp, while the rod D, passing through 
the base A, in an insulating tube, formed 
the other terminal. Between the terminals 
F and D, were two rods of carbon, so 
arranged that one only was in circuit at 
any one time. The thinner central por- 
tion of these rods was heated to incan- 
descence by the electric current passed 
through the lamp, while the thicker por- 
tions O, O, served to cool the extremities, 
at the points of contact with the support- 
ing frame. After the first rod was con- 
sumed, it dropped out of position, and 
allowed the second rod to replace it. When 



82 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 4. BOULIGUINE'S LAMP. 



EARLY HISTORY. 33 

the second rod was consumed, the lamp be- 
came automatically short-circuited. The 
difficulty with this lamp was the too rapid 
consumption of the carbons. 

In 1876 an improvement was made by 
Boulyguine, who produced a lamp intended 
to obviate this difficulty. In Boulyguine's 
lamp, the carbon is automatically fed 
upwards as it consumes away. A section 
of this lamp is shown in Fig. 4. Here the 
lower holder of the carbon rod has a slide 
in which guides press upwards under gravi- 
tational force, and feed the carbon filament 
up against the upper electrode as the short 
rod or filament is consumed. 

Fig. 5, shows a form of Sawyer lamp. 
Here the light-giving medium consists of 
an incandescent carbon pencil at the top 
of the lamp. This consumes away slowly 



34 ELECTRIC INCANDESCENT LIGHTING. 



FIG. 5. SAWYER'S LAMP. 



EARLY HISTORY. 35 

in operation at its contact with the upper 
carbon block, at the rate of about ^th 




FIG. 6. FARMER'S LAMP. 

inch per hour. The carbon pencil was 
about eight inches in length and was 
forced upwards as consumption took place. 
The lamp was mounted in a glass globe 
partially exhausted. 



36 ELECTRIC INCANDESCENT LIGHTING. 

Fig. 6, shows an early form of carbon 
lamp introduced by Farmer in 1879. 
Here a short horizontal carbon rod is 
gripped between two large metallic blocks 
in the exhausted globe. 

All the lamps we have hitherto de- 
scribed have proved commercially useless, 
in the forms in which they were presented. 
What might have been the effect of intro- 
ducing slight modifications into such lamps 
is beyond the province of this volume to 
consider. There can, however, be but 
little doubt that the want of a cheap 
source of electric current stood as much 
in the way of the progress of electric in- 
candescent lighting, as any glaringly in- 
herent difficulty in the structure of the 
lamps themselves. 

Before leaving this brief history of the 



EARLY HISTORY. 37 

early forms of incandescent lamps, it may 
be well to discuss some of the many forms 
that were devised for burning in the open 
air. These lamps strictly speaking were of 
a type which may be best described as semi- 
incandescent lamps. They operate essen- 
tially on the principle of sending a current 
through a slender rod of carbon pressed 
against a block or larger mass of the same 
material. Under these circumstances the 
slender rod is raised to intense incandes- 
cence, especially at its point of contact 
with the larger electrode, where, in reality, 
a miniature arc is formed. Various de- 
vices were employed in lamps of this type 
for feeding the carbon rod or pencil as it 
was gradually consumed. In some lamps 
an enclosing glass chamber was employed 
in order to reduce the consumption of the 
carbon as far as possible. This type of 
lamp passes insensibly into lamps of the 



38 ELECTKIC INCANDESCENT LIGHTING. 

purely incandescent form. In fact, as will 
be observed, some of the preceding lamps 
were of the seini-incandescent type. 







FIG. 7. REYNIEB'S LAMP. 



One of the most successful of the early 
lamps of the semi-incandescent type was 
that of Keynier. In the Reynier lamp a 
movable rod of carbon C\ Fig. 7, of small 
diameter, supported as shown, rests against 



EAEL' 



a contact block 

to limit the incandesce 

lower extremity, a lateral 




FIG. 8. REYNIER'S LAMP. 

is kept pressed against the rod <7, by 
means of a spring R. The current, there- 
fore, passes through the lateral contact 
piece Z, through the slender rod to the 
contact block of graphite J5, so that only 
the portion of the rod between these 



40 ELECTRIC INCANDESCENT LIGHTING. 

points is rendered incandescent, by far the 
greatest amount of light coming from the 
tip or extremity J. Fig. 8, is a semi-dia- 
grammatic view of the same lamp ar- 
ranged, however, to be used in connection 
with an external globe. The two binding 
posts at the top of the lamp form its 
terminals. No vacuum is necessary with 
this form of lamp since the slender rod of 
carbon is fed downwards as the point con- 
sumes away. 

In 1878 an Englishman, named Werder- 
mann, took out a patent for a lamp 
founded on a somewhat similar principle. 
In the Werdermann lamp, shown in Fig. 9, 
as in the Reynier lamp, means were devised 
for pressing a slender carbon rod against a 
fixed electrode, and feeding this rod up- 
wards as it consumed away. Werdermann 
employed for his fixed electrode a carbon 



EARLY HISTORY. 41 

disc and advanced a slender carbon rod by 
the action of a weight or counterpoise. In 
order to avoid the casting of shadows 
downwards, a notable defect in the 




FIG. 9. WERDERMANN'S LAMP. 

Reynier lamp, Werdermann inverted his 
lamps, as shown in the figure. Lamps of 
the combined Reynier- Werdermann type 
at one time were in fairly successful practi- 
cal use, and formed one of the features 



42 ELECTRIC INCANDESCENT LIGHTING. 

of the Electrical Exhibition of 1881 at 
Paris. 

The advent of the really successful in- 
candescent lamp dates from about 1879, 
and from this year, the growth of the in- 
candescent electric lamp industry has been 
extremely rapid. The year 1879, there- 
fore, marks the entrance to the epoch of 
contemporaneous history, into which we 
are unable to enter at the. present time. 
We will, therefore, close this extremely 
brief history of the art, referring the 
reader for further particulars to contem- 
poraneous literature. 



CHAPTER III. 

ELEMENTARY ELECTRICAL PRINCIPLES. 

THE light emitted by the glowing fila- 
ment of an incandescent lamp is one of the 
effects produced by the passage of the 
electric current through it. Before pro- 
ceeding to a discussion of the operation 
of the incandescent electric lamp, it will 
be necessary to consider briefly the lead- 
ing elementary principles concerning the 
production and flow of electricity. 

An electric flow is always produced by 

the action of. what is termed electromotive 

foi*ce, generally contracted E. M. F. No 

electric source produces electricity directly. 



44 ELECTRIC INCANDESCENT LIGHTING. 

What is produced is an electromotive 
force, and an E. M. F., in its turn, pro- 
duces an electric current when permitted 
to do so. Thus, in such an electric 
source as a voltaic battery, an E. M. F. 
is produced, and this independently of 
whether it is permitted to establish an 
electric current or not. If an E. M. F. be 
permitted to act, it will invariably establish 
an electric current. In order to do this 
a conducting path must be opened to it. 
Such a conducting path is called a circuit. 

For convenience, it is universally agreed 
to regard electricity as leaving an electric 
source at the point called the positive 
terminal or positive pole, and re-entering 
the source, after having passed through 
the circuit, at a point called the negative 
terminal or negative pole / that is to say, 
electricity is regarded as flowing from the 



ELEMENTARY ELECTRICAL PRINCIPLES. 45 

positive to the negative pole, in the ex- 
ternal portion of the circuit, and from the 
negative to the positive pole, in the internal 
portion of the circuit, that is within the 
source. 

Since all electric currents are due in 
the first instance to the action of an E. 
M. F., it is necessary to obtain definite 
ideas concerning this force. E. M. F. is 
to electric flow the analogue of ordinary 
pressure to the flow of liquids or gases; 
that is to say, a flow or current never 
occurs in a liquid or gas, except as the 
result of difference of pressure acting 
on it, and the liquid or gaseous flow is 
always directed from the point of higher 
pressure to the point of lower pressure. 
So in the electric circuit, a current of elec- 
tricity never flows unless there be a differ- 
ence of electric pressure, or an E. M. F., 



46 ELECTRIC INCANDESCENT LIGHTING. 

and the electric flow is always directed 
from the point of higher to the point of 
lower electric pressure. 

E. M. F. is measured in units called 
volts. Thus, a voltaic cell, of the type 
known as a Leclanche cell, has an E. M. F. 
of, approximately, 1 1/2 volts. Such a 
cell is shown in Fig. 10. A carbon plate 
CGC, is connected to the positive terminal 
JP, while a rod of zinc Z Z, is connected to 
the negative terminal N. This cell pro- 
duces, when in good order, an E. M. F. 
of about 1 1/2 volts, even when on open 
circuit, that is when the terminals jP, and 
N, are disconnected as shown, and are, 
therefore, producing no current. If, how- 
ever, these terminals be connected through 
a conducting path, or circuit, a current of 
electricity will flow under the pressure of 
1 1/2 volts, from the positive terminal jP, 



ELEMENTARY ELECTRICAL PRINCIPLES. 47 

through the external portion of the circuit 
back to the negative pole N, and from the 




FIG. 10. LECLANCHE CELL. 

zinc plate through the solution S xSJ to the 
positive terminal, thus completing a cir- 
cuital path. 



48 ELECTRIC INCANDESCENT LIGHTING. 

When an E. M. F. greater than 1 1/2 
volts is required, from cells of this type, a 
number of such cells are so connected to- 
gether as to act as a single source. Such a 
combination of cells is called a battery. If, 
for example, two such cells be joined to- 
gether, with the negative pole of one cell 
connected to the positive pole of the other, 
they would produce a battery of three volts 
E. M. F., and 100 such cells connected in 
this way, or connected in series, as it is 
called, would produce a battery having 
a total E. M. F. of approximately 150 
volts. 

Voltaic batteries are seldom employed 
for supplying current to incandescent 
lamps except on a small scale, for the 
reason that the cost of the current so pro- 
duced would be excessive. In almost all 
cases of electric lighting, the E. M. F. is 



ELEMENTARY ELECTRICAL PRINCIPLES. 49 

obtained from a dynamo-electric generator, 
a machine for producing electric power 
by the expenditure of mechanical power. 
Dynamo-electric machines, suitable for 
incandescent lighting, will be considered 
in a subsequent chapter. 

When an E. M. F. is permitted to act 
upon a closed conducting path or circuit, 
the value of the current strength produced 
therein, that is, the amount of electricity 
which flows in a given time, will depend 
upon two circumstances ; namely, 

(1) Upon the value of the E. M. F.; 
i. e.j the number of volts. 

(2) Upon a property of the circuit 
called its electric resistance, that is to say, 
the opposition it offers to the flow or pas- 
sage of electricity through it. Thus, if 
the cell shown in Fig. 10 has an E. M. F. 
of 1 1/2 volts, and produces a much 



50 ELECTRIC INCANDESCENT LIGHTING. 

greater current strength in fa one circuit 
than in another, it is because the latter 
circuit offers a greater resistance to 
the flow of electricity than the former. 
Some idea of the action of resistance, in 
opposing the flow of electricity in an 
electric circuit, can be had by consider- 
ing the analogous case of the flow of gas 
through a pipe or main. A long narrow 
pipe will obviously offer a greater resist- 
ance to the passage of gas through it, 
from a reservoir, than a larger short pipe. 

The resistance of an electric circuit is 
measured in units of electric resistance 
called ohms. The ohm is a resistance such 
as is offered by about two miles of ordinary 
overhead trolley wire, or about one foot of 

very fine copper wire, No. 40 A. W. Gr., which 

3 
has a diameter of about Tth inch. 



PROPERTY Of'; 

ELEMENTARY ELECTI$fr$ PRINCIPLES. 51 > 




The electric 

very important quantity. 
resistances will, therefore, be of interest. 

An ordinary Bell telephone receiver has 
a resistance of about 75 ohms. 

An ordinary telegraph sounder has a re- 
sistance of about 2 ohms. 

An ordinary incandescent lamp, of 16 
candle-power, intended for 11 5- volt circuits, 
has a resistance, when lighted, of about 
250 ohms. 

The electric resistance of a conductor 
depends upon its length, its cross-sectional 
area, and upon the nature of the material 
of which it is composed. The resistance 
increases directly with the length of con- 
ductor, and inversely as the cross-sectional 
area. Thus, if a mile of trolley wire, 
weighing 1,690 Ibs. has a resistance of 
1/2 ohm, two miles will have a resistance 



52 ELECTRIC INCANDESCENT LIGHTING. 

of one ohm, and 10 miles, a resistance of 5 
ohrns. If the above trolley wire be 
doubled in cross-sectional area, and, conse- 
quently, in weight, so as to weigh 3,380 Ibs. 
per mile, its resistance will be only 1/4 
ohm per mile, or 2 1/2 ohms in 10 miles. 

The resistance of wires, each a mile long, 
and of the same diameter as ordinary 
trolley wire, (0.325") would be different 
with different materials. Thus, while such 
-a wire of copper, has a resistance of about 
1/2 an ohm, an iron wire of the same size, 
length and diameter, would have a resist- 
ance about 6 1/2 times greater, or about 
31/4 ohms, and when of lead, about 12 
times greater, or about 6 ohms. Conse- 
quently, in order to compare the relative 
resistance of wires of different materials, it 
is necessary to refer each material to a com- 
mon standard of dimensions. This is done 



ELEMENTARY ELECTRICAL PRINCIPLES. 53 

by considering the resistance of a wire 
having unit length and unit cross-sectional 
area, that is to say, the resistance of a wire 
having a length of one centimetre and a 
cross-sectional area of one square centi- 
metre. The resistance of a wire with such 
unit dimensions is called its specific resist- 
ance or its resistivity. The resistivity of 
standard soft copper is 1.594 microhms; 
i. <?., 1.594 millionths of one ohm. If then 
a wire has a length of one kilometre (100,- 
000 centimetres) and a cross-sectional area 
of 1 square centimetre, it would have a re- 
sistance of 1.594 x 100,000 microhms = 
1.594 X 100,000 

1,000,000 ai 94 ohm > at the tem - 

perature of melting ice. 

The resistivity of a wire is the scientific 
standard for comparing its resistance with 
that of other wires of the same length and 



54 ELECTRIC INCANDESCENT LIGHTING. 

cross-sectional area. In English-speaking 
countries, where the centimetre is not in 
general use as the unit of length, the stand- 
ard called the circular-mil-foot is very 
commonly employed. A circular-mil is 

the area of a wire one mil, or 



an inch, in diameter. This is not to be 
confused with the area of such wire ex- 
pressed in square inches. The number of 
circular mils cross-sectional area in any 
wire, is obtained by squaring its diameter 
in mils. Thus a wire half an inch in 
diameter, would be a wire of 500 mils 
diameter, and the number of circular mils 
cross-sectional area in such wire would 
be 500 X 500 = 250,000. Such a wire 

would have a resistance per foot of ^ '' ^ 

250,000 

= 0.000,00414 ohm. A circular-mil-foot 
of standard soft copper at 20 C. has a 
resistance of 10.35 ohms. 



ELEMENTARY ELECTRICAL PRINCIPLES. 55 

The resistivity of a material varies with 
its temperature. In the case of most me- 
tallic substances, the resistivity increases 
as the temperature increases. Thus, the 
resistivity of copper wire is about forty- 
two per cent, greater at the boiling point of 
water, than at its freezing point ; or, a cop- 
per wire would have about forty-two per 
cent, more resistance, at the temperature of 
the boiling point of water, than at its freez- 
ing point. The resistivity of insulating 
materials, however, diminishes as the tem- 
perature increases. Carbon behaves in 
this respect like an insulating material, its 
resistivity diminishing as its temperature 
increases. An ordinary incandescent lamp 
has about twice as much resistance when 
cold, as it has when heated by the electric 
current to an incandescent temperature. 

The current strength, which passes 



56 ELECTRIC INCANDESCENT LIGHTING. 

through any circuit, is measured in units 
of electric flow called amperes. As in the 
case of a current or flow of gas, we may 
estimate the flow as so many cubic feet of 
gas per minute, or per second, so an electric 
flow, may be estimated as so many units 
of electric quantity per second. The unit 
of electric quantity is called the coulomb, 
and is the quantity of electricity, which 
would flow in one second through a cir- 
cuit having a total resistance of one ohm, 
when under a pressure of one volt. A 
rate of flow equal to one coulomb-per- 
second is the unit of electric flow or cur- 
rent, and is called the ampere. A current 
of 10 amperes, therefore, means a flow, or 
transfer, of 10 coulombs of electricity in 
each second. The ordinary incandescent 
lamp of 16 candle-power, operated at a 
pressure of 115 volts, requires to be sup- 
plied with a current of about 1/2 ampere. 



ELEMENTARY ELECTRICAL PRINCIPLES. 57 

The relations existing in any circuit 
under a given resistance and E. M. F. are 
readily determined by reference to a law 
discovered by Dr. Ohin, and named Ohm's 
Law. This law may be expressed briefly 
as follows : 

The current strength in any circuit is 
directly proportional to the total E. M. F. 
acting in the circuit, and inversely pro- 
portional to tlie total resistance in the 
circuit. 

If the pressure or E. M. F. be measured 
in volts, and the resistance in ohms, 
the current strength that passes in am- 
peres may be briefly expressed as follows: 

Volts 

Amperes = ^- r - 
Ohms 

For example, if a circuit comprise a 
dynamo and an external path consisting 
of lamps and wires, so that the E. M. F. 
in the dynamo is 100 volts, and the resist- 



58 ELECTRIC INCANDESCENT LIGHTING. 

ance of .. the circuit is 2 olnns, then the 
current strength passing through the cir- 

cuit will be - - = 50 amperes. 

a 

Again, if an incandescent lamp has a 
resistance (hot) of 220 ohms, and is con- 
nected to a pair of mains between which 
the electric pressure is steadily maintained 
under all circumstances at 110 volts, then 
the current, which will pass through the 

110 1 
lamp irom the mains will be 

ampere. 



We have already alluded to the fact 
that a current never flows in water unless a 
difference of pressure exists therein. In 
order to produce this difference of pressure, 
the water has usually to be raised to a 
higher level ; and, to do this, energy is re- 
quired to be expended, or work performed, 



f PROPERTY OF 



ELEMENTARY ELECTK~ ~" 

on the water. The 

tricity. In order to produce an electric 
flow, energy requires to be expended, or 
work produced, by the electric source. 

Work is never done unless force acts 
through a distance. A force that is 
merely producing a pressure on a body, 
but no motion of the body, is naturally 
performing no work. When, for example, 
a block of granite is raised through a 
vertical distance against the earth's gravi- 
tational force, work is done. The amount 
of such work is measured by the force 
which acts, multiplied by the distance 
through which it acts. For example, if 
a block weighing 200 pounds be raised 
through 10 feet, an amount of work will 
be done expressed in a common unit of work 
called the foot-pound, as being equal to 
200 pounds X 10 feet = 2,000 foot-pounds. 



60 ELECTKIC INCANDESCENT LIGHTING. 

If this weight when raised be placed on 
a shelf or other support, it would still 
produce a pressure, of 200 pounds upon 
the support, but would be doing no 
work. 

Another unit of work is called the joule, 
and is approximately equal to 0.738 foot- 
pound, so that a foot-pound is about thirty- 
five per cent, greater than a joule, or 1 
foot-pound = 1.356 joules. A man weigh- 
ing 150 pounds, and raising his weight 
through a distance of 100 feet by walking 
upstairs/ necessarily performs an amount 
of work against gravitational force equal 
to 100 X 150 = 15,000 foot-pounds = 
20,340 joules. 

When an electric current passes through 
a circuit, work is always done by the E. 
M. F. which drives the current through the 



ELEMENTARY ELECTRICAL PRINCIPLES. 61 

circuit. The amount of work done by 
the E. M. F. is expressed in joules, as the 
product of the pressure and the quantity 
of electricity it drives. Thus, if a quan- 
tity of electricity equal to 100 coulombs, 
passes through an electric circuit under 
a pressure of 50 volts, then the amount 
of work which will be expended in 
the passage, will be 50 X 100 = 5,000 
joules = 3,690 foot-pounds. A joule is, 
therefore, equal to a volt-coulomb. This 
work will always be taken from the 
source of the driving E. M. F. Thus if 
the dynamo in the last example, supplied 
the E. M. F., then an amount of work 
equal to 5,000 joules will have been taken 
from the dynamo, and this amount of work 
must have been delivered to the dynamo 
through its driving belt. Or, if the E. 
M. F. had been supplied by a voltaic 
battery, this amount of work would have 



62 ELECTRIC INCANDESCENT LIGHTING. 

been supplied at the expense of the zinc and 
the liquid in the battery ; that is to say a 
certain amount of zinc would have been 
consumed, thereby liberating at least 5,000 
joules of work. 

It is necessary to distinguish carefully 
between the amount of work performed in 
any case and the rate at which such work 
is performed ; for example, so far as the 
result attained is concerned, the same 
.amount of work is done, when the man be- 
fore alluded to, weighing 150 pounds, raises 
himself through a height of 100 feet by 
the stairs, whether he performs this work 
in one minute or in ten minutes, but his 
rate-of-doing-ioork, or his activity would be 
10 times greater in the former than in the 
latter case. In the former, his activity 
would be 15,000 foot-pounds-per-minute, 
or 250 foot-pounds-per-second, while in the 



ELEMENTARY ELECTRICAL PRINCIPLES. 63 

latter case it would be only 1,500 foot- 
pounds-per-minute, or 25 foot-pounds-per- 
second. Activity is commonly rated either 
in terms of a unit of activity called a 
foot-pound-per-second, or in a unit called a 
horse-power, one horse-power being equal to 
550 foot-pounds-per-second, or 33,000 foot- 
pounds-per-minute. Thus, in the preced- 
ing case, the man would be expending an 

250 
activity of - = 0.455 horse-power in the 



first case, and 0.0455 horse-power in the 
second case. 

Electric activities are similarly measured 
in units of electric power or activity called 
watts, the watt being equal to an activity 
of a joule-per-second, or a volt-coulomb-per- 
second, or a volt-ampere. 

Thus if a current of 1/2 ampere passes 



64 ELECTRIC INCANDESCENT LIGHTING. 

through an incandescent lamp under a 
pressure of 115 volts, the electric activity 
or rate of expending energy in the lamp, 
will be 115 x 1/2 = 57.5 watts, or joules- 
per-second = 42.4 foot-pounds-per-second. 



CHAPTER IV. 

PHYSICS OF THE INCANDESCENT ELECTRIC 
LAMP. 

BEFORE proceeding to a detailed descrip- 
tion of the incandescent lamp and the 
methods employed in its manufacture, it 
will be advisable to obtain a general in- 
sight into the physical laws controlling its 
operation. 

Briefly speaking, the operation of the 
incandescent electric lamp is based upon 
the principle of raising the temperature of 
a thin thread or filament of some refrac- 
tory substance, such as carbon, as far as 
is consistent with practical working. In 



G5 



66 ELECTRIC INCANDESCENT LIGHTING. 

order to avoid the oxidation of the carbon 
filament, it is enclosed in a glass lamp bulb 
in which a vacuum is maintained. Briefly, 
the function of the electric lamp is to 
convert electric energy economically into 
.luminous energy or light. 

Light may be defined in two distinct 
senses. 

First, subjectively, as the physiological 
effect produced through the eye on the 
mind by the radiations emitted by a 
luminous body. In this sense, lights 
differ in their color and intensity ; that is, 
we are conscious of different perceptions 
both of color and of intensity. 

Second, objectively, as the physical 
cause which produces the sensation of 
light. In this sense light can have an 
existence independent of the eye. Objec- 
tively, light consists of rapid vibrations or 



PHYSICS OF INCANDESCENT LAMP. 67 

to-and-fro motions in a medium called the 
universal or luminiferous ether, which 
permeates all substances and spaces. 

The luminiferous ether is believed to 
be an extremely tenuous and highly elastic 
medium, which not only fills interstellar 
space, but which even permeates the 
densest forms of matter. In this sense 
any vibrations, or to-and-fro motions, of the 
luminiferous ether, even though not capable 
of affecting the eye, are properly spoken 
of as light, but of course the light, which 
it is the function of the incandescent lamp 
to produce for the purposes of illumina- 
tion, must necessarily be light in the 
physiological sense. 

The rapidity of the oscillations in the 
ether which constitute light is usually 
enormously great. This frequency has 



68 ELECTRIC INCANDESCENT LIGHTING. 

been indirectly measured up to over 800 
trillions; i. e., over 800,000,000,000,000 
double vibrations per second, and they 
may exist down to comparatively low fre- 
quencies, although they have only been 
measured in heat radiation as low as about 
100 trillions per second. Those frequen- 
cies which lie between 390 trillions and 
760 trillions, are capable of affecting the 
normal eye as physiological light. 

All bodies emit from their surfaces 
radiations or waves into surrounding space. 
A body at ordinary temperatures emits 
only waves of a comparatively low fre- 
qiiency, far below that which is capable 
of affecting the eye physiologically as 
light. As the temperature of the body is 
increased, not only does it emit these 
waves of low frequency more powerfully, 
but, in addition, it also emits waves of a 



PHYSICS OF INCANDESCENT LAMP. 69 

higher frequency. When a tempera- 
ture of about 500 C. is reached, the 
highest frequency emitted by the body 
will be just about 390 trillions of double 
vibrations, or complete to-and-f ro motions, 
per second, and will be just visible to the 
eye. The body is then said to be at the 
temperature of dull red. As the tempera- 
ture is still further increased, the total 
radiation of waves from the surface in- 
creases, and at the same time higher fre- 
quencies are introduced. These affect the 
eye successively as orange, yellow, green, 
blue, indigo and violet ; and, finally, all 
these colors being present, the body is 
said to be white hot, and has a tempera- 
ture of roughly 1,500 C. If the tempera- 
ture be still further increased, the lumi- 
nous intensity ; i. e. 9 the amount of visible 
radiation per unit area of its surface, will 
increase, and at the same time still higher 



70 ELECTRIC INCANDESCENT LIGHTING. 

frequencies will be introduced into these 
vibrations, which are necessarily invisi- 
ble to the eye. These are called ultra- 
violet rays, or those rays above the 
violet. 

If we analyze sunlight, we will find that 
it contains all frequencies from the lowest 
that we can measure up to the ultra-violet. 
The greatest intensity of these vibrations 
falls within the limits of the invisible fre- 
quencies, only about thirty per cent, of the 
vibrations which we receive at the earth's 
surface being capable of affecting the eye. 
The visible frequencies combine to pro- 
duce on the eye an impression, known as 
white light. In other words we judge a 
luminous body as white, when it emits 
frequencies of the character and general 
proportions which exist in sunlight, or the 
relative proportions of red, green, yellow, 




PHYSICS OF INCAN 

and blue frequencies or 
the same in this light as in 

Generally speaking, nearly all sources of 
artificial light emit frequencies which are 
the same as those in sunlight, but the 
amount of radiation in the different fre- 
quencies or colors varies markedly from 
sunlight. Thus a candle while emitting 
all the visible frequencies of sunlight 
has a marked preponderance of red rays 
relative to the number of violet rays, 
and consequently has a reddish yellow 
tint. 

The color of a body depends upon two 
things ; viz. , first upon the quality of the 
light it receives, that is upon the propor- 
tionate distribution of the various frequen- 
cies, and second upon the selective proper- 
ties of its surface. When light falls on a 



72 ELECTEIC INCANDESCENT LIGHTING. 

colored body, the surface of the body pos- 
sesses the power of absorbing some of the 
frequencies and throwing off others unab- 
sorbed. Thus, a blue body, illumined by 
sunlight, absorbs practically all the frequen- 
cies except those of the blues, which it emits. 
For the blue body to be visible in its proper 
tint, therefore, it is necessary that the light 
which illumines it shall not only contain 
blues, but shall also contain the same pro- 
portionate quantities of the different tints 
of blue as sunlight. If these colors be not 
present in the artificial light, such a blue 
body would fail to possess its character- 
istic daylight color-value. Consequently, 
an artificial illuminant, in order to replace 
sunlight for the purpose of revealing the 
proper daylight color-values of bodies, 
must contain not merely the same fre- 
quencies as" sunlight, but also the same 
relative distribution of such frequencies. 



PHYSICS OF INCANDESCENT LAMP. 73 

All light serves either to distinguish the 
form and shape of bodies, or their colors. 
For the latter, as we have seen, an approx- 
imate imitation of sunlight is necessary; 
for the former, almost any frequency of 
light will be sufficient. For example, if 
differently colored bodies be observed in 
a dark room, by means of an artificial 
light containing practically but one fre- 
quency, and called usually a monochro- 
matic light, only the color of this light 
will be visible, all other colored objects 
will appear black, or devoid of color. A 
yellow, monochromatic light, may be ob- 
tained, for example, by the burning of 
alcohol on a wick soaked in common salt. 
In the pure yellow light this emits, all 
yellow colored objects will appear in 
nearly their true tints, while the reds, 
blues, greens, and other tints will appear 
devoid of color. All objects, however, 



74 ELECTRIC INCANDESCENT LIGHTING. 

whatever their color, will show their form 
even when so illumined. 

The light emitted by an incandescent 
electric lamp is not capable of giving true 
sunlight color-values. An analysis of the 
light from the glowing filament, shows a 
relative preponderance of red and yellow 
rays and a deficiency of the blue and 
violet, or high-frequency waves. This is 
owing to the fact that the temperature 
of the glowing filament cannot be raised 
sufficiently high to emit the sunlight pro- 
portions of the higher frequencies. Con- 
sequently, reds and yellows, viewed by 
incandescent lamp light, give nearer ap- 
proach to their sunlight values than other 
colors. It is true that by raising the 
temperature of the carbon filament we 
obtain a closer approach to sunlight radia- 
tion, but, at the same time, for reasons 



PHYSICS OF INCANDESCENT LAMP. 75 

which will be subsequently explained, 
the life of the lamp is greatly shortened. 

A hot body loses its heat in one of four 
ways ; viz., by radiation, by conduction, 
by convection and by molecular transfer. 

Were the glowing filament in an abso- 
lutely vacuous space, it is evident that being 
supported on a comparatively slender 
base, apart from the trifling loss of heat 
through this base or support there would 
be no other means for losing the heat save 
by radiation. Once admitting within the 
lamp chamber even a minute trace of gas 
such as would make the pressure one- 
millionth part of that in the atmosphere, 
then pure radiation would cease to form 
the sole means of losing heat, and 
molecular transfer would begin to act. 
That is to say the air molecules coming 



76 ELECTRIC INCANDESCENT LIGHTING. 

into contact with the heated filament 
would be shot off from its surface in 
straight paths, and, in a highly attenuated 
atmosphere, the molecules would nearly 
all fly to the chamber walls without 
mutual collision. Heat energy is required 
to produce this motion, and the loss of 
energy so occasioned forms an additional 
means whereby a heated body in a rarified 
atmosphere parts with its heat. 

As more air is admitted to the interior 
of an exhausted lamp, the collisions of the 
air molecules, flying from the heated surface, 
become more frequent, and the frequency 
with which they are returned to the hot 
surface also increases, increasing thereby 
the loss of heat by molecular transfer. As 
soon, however, as the mean free paths, or 
uncollided path, of the molecules becomes a 
small fraction of the distance between the 



PHYSICS OF INCANDESCENT LAMP. 77 

filament and the wall of the chamber, 
the frequency with which the molecules 
return to be shot off from the hot surface 
increases very slowly, so that beyond this 
point there is scarcely any increase in loss 
of heat by molecular transfer as air is 
admitted into the chamber. As more air 
is gradually admitted into the chamber, 
however, the loss by simple convection 
increases, i. e., by a thermal stirring of the 
air owing to differences of density, or local 
winds, within the lamp chamber. 

The radiation emitted by the ordinary 
incandescent electric lamp is principally 
non-luminous; that is to say the greater 
portion possesses a frequency below the 
inferior limit of visibility. An ordinary 
16-candle-power lamp has an activity, 
when in operation, of about 50 watts. 
Of this activity about 48 watts are ex- 



78 ELECTRIC INCANDESCENT LIGHTING. 

pended in non-luminous radiation, and 
only about 2 watts, or four per cent., in 
luminous radiation. The problem that still 
remains to be solved in the incandescent 
lamp, as it does indeed in the case of all 
artificial illuminants, is to produce a radia- 
tion which shall lie wholly, or almost 
wholly, between the limits of visible fre- 
quencies. As it exists to-day, in the case 
of the incandescent lamp, the energy is 
expended in producing about ninety-six 
per cent, of objectionable heat radiation, 
and four per cent, of light radiation. Even 
this, however, has a luminous efficiency 
superior to that of gas and oil. 

It has been found that the light emitted 
by the firefly and the glow-worm is prac- 
tically confined to the visible limits of 
frequency. Could an incandescent lamp 
be made to restrict its radiation to such 



PHYSICS OF INCANDESCENT LAMP. 79 

frequencies, the problem of cheap light 
might be solved. Unless, however, such 
light could be made to possess these fre- 
quencies in sunlight proportions, it is 
question able whether the problem of an 
efficient illuminant would be solved from 
the color standpoint. 

Passing by the question of the produc- 
tion of lamps which shall yield fre- 
quencies characteristic of the light of the 
firefly and glow-worm, there would appear 
to remain but one direction in which the 
same result might be reached; namely, 
by obtaining a substance which possessed 
marked powers of selective radiation ; that 
is, a high ability to radiate waves of high 
frequency, and but little for radiating 
those of low frequency. 

When an electric current is sent through 



80 ELECTRIC INCANDESCENT LIGHTING. 

the filament of an incandescent lamp, the 
activity expended in the lamp will be the 
product of the pressure at the lamp termi- 
nals in volts, and the current, in amperes, 
passing between them. This activity will 
be entirely expended as heat in the sub- 
stance of the filament, and this heat will 
be liberated from the surface in virtue of 
the increase of temperature of that surface. 
As the amount of heat liberated in the 
filament increases ; i. e., as the current 
strength passing through it increases, the 
temperature of the filament is compelled 
to rise in order to emit the activity which 
is developed in its mass. If the surface of 
the filament be large, it will take a large 
total amount of activity in the lamp to 
maintain a large radiation per square 
inch, or per square centimetre ; whereas, 
if the surface of the filament be small, the 
opposite result will be produced. Con- 



PHYSICS OF INCANDESCENT LAMP. 81 

sequently, a certain relation must exist 
between the surface, the length, and the 
cross section of the filament, in order that, 
at the pressure intended for the circuit, 
the radiation per square inch, or per square 
centimetre, shall be sufficient to bring the 
lamp to the proper temperature. The 
nature of the surface of the filament deter- 
mines, to a great extent, the character and 
amount of the radiation which it will emit. 
It might be supposed that the same activity 
per square centimetre of surface would be 
attended by the same temperature and rela- 
tive distribution of vibration frequencies. 
Such, however, is not the case, the charac- 
ter of the surface having a marked influ- 
ence upon its emissivity, one type of carbon 
producing, with a given activity of sur- 
face, a greater amount of light than another. 

The temperature at which ordinary in- 



82 ELECTRIC INCANDESCENT LIGHTING. 

candescent lamp filaments are operated, 
is estimated at about 1,345 C. If this 
temperature be 'exceeded, by only a few 
degrees, although the candle-power of the 
filament will be materially increased, yet 
the disintegration of the carbon, by a 
process akin to evaporation, will be rap- 
idly brought about. Thus, an increase of 
2 C. is believed to be accompanied by 
an increased candle-power of about three 
per cent., but this gain is at a marked 
decrease in the life of the lamp. 



^nw 







PROP, 



'ffry OF 



\ki<V 



CHAPTER V. 

MANUFACTURE OF INCANDESCENT LAMPS. 
PREPARATION AND CARBONIZATION OF 
THE FILAMENT. 

THE most important step to be taken 
in the manufacture of an incandescent elec- 
tric lamp is the preparation of the fila- 
ment. Of all substances which have been 
employed for filaments, carbon alone has 
been found to meet the requirements of 
use. In the first place, carbon is highly 
refractory ; that is, capable of withstand- 
ing a high temperature before reaching its 
point of volatilization. In the next place, 
its resistivity is high, so that a high resist- 
ance can be readily given to a short length 



84 ELECTRIC INCANDESCENT LIGHTING. 

of filament, with a correspondingly high 
electric pressure at the terminals, for a 
given activity in the lamp. 

Carbon is universally employed for 
lamp filaments, not only for the reasons 
above pointed out, but because this 
material readily lends itself to being 
fashioned and shaped into the filament,, 
prior to being subjected to various proc- 
esses of carbonization, intended to ensure 
a nearly pure form of hard high-resisting 
carbon. 

A great variety of materials have been 
employed for producing the carbon fila- 
ments of incandescent lamps. All these 
substances agree in that they are of such a 
nature as will yield a nearly pure carbon 
when subjected to carbonization, i. e., to 
the action of heat while out of contact 



PREPARATION OF THE FILAMENT. 85 

with air. Substances suitable for this pur- 
pose may be divided into two sharply 
marked classes ; namely, 

(1) Carbons of fibrous origin, such as 
bamboo. 

(2) Structureless carbons, such as pastes 
or mixtures of finely ground carbon incorpo- 
rated with some suitable carbonizable liquid. 

Among substances of fibrous origin, that 
have been employed for incandescent fila- 
ments, may be mentioned paper, bamboo, 
bass fibre, cotton thread, and silk thread, 
both of the latter substances being first 
subjected to a process which is called the 
parchmentizing process, by treatment with 
sulphuric acid. Cellulose, treated in such 
a manner as to be converted into a variety 
of gun-cotton and subsequently carbonized, 
has also been employed. This material, 
although of fibrous origin, would by its 



86 ELECTRIC INCANDESCENT LIGHTING. 

treatment be rendered capable of classifica- 
tion as structureless material. Without 
here entering into a full description of the 
various processes required for the manu- 
facture of filaments from the above 
materials, it will suffice to describe in 
detail the process adopted in a few cases. 

In the manufacture of a bamboo fila- 
ment, carefully selected bamboo is em- 
ployed, from which both the softer por- 
tions in the interior, and the hard silicious 
parts near the surface, have been removed. 
The material is then cut or fashioned, by 
the aid of a cutting tool, into filamentary 
strips, care being taken to obtain as nearly 
as possible the same area of cross section 
by passing the filaments through gauges. 
The filaments so prepared are then con- 
verted into hard carbon by means of a car- 
bonizing process. 



PREPARATION OF THE FILAMENT. 87 

In the production of a filament from 
loosely spun pure cotton, the thread is first 
cleansed from grease by boiling in soda or 
ammonia, this cleansing being necessary for 
ensuring uniformity of action on the part 
of the sulphuric acid used in a subsequent 
process. The thread is then thoroughly 
washed in water and afterward soaked in 
sulphuric acid of specific gravity 1.64. 
The time of immersion is exceedingly 
short, varying with the thickness and char- 
acter of the thread, from three to fifteen 
seconds. On removal from the acid, the 
thread is 'again washed in water. After 
removal from the water, care must be 
taken to avoid warping. The dried thread 
in this condition has the appearance of 
catgut and is called amyloid. 

The parchmentized thread has a rough 
surface, and is too irregular in diameter to 



88 ELECTRIC INCANDESCENT LIGHTING. 

permit it to be subjected in this condition 
to the carbonizing process. In order to 
ensure uniformity in its diameter, and 
smoothness of its surface, it is passed 
through a series of draw plates, until a 
sufficient amount has been removed from 
it to permit the cutting tool to act on all 
portions of its surface. These draw plates 
are made either of steel, or of jewels, the 
latter being the most frequently employed. 
The thread so produced is then subjected 
to the carbonizing process. 

Another process, which also produces an 
amyloid thread from pure cellulose, is 
sometimes employed. Here pure cellulose 
is dissolved at a temperature of about the 
boiling point of water, in zinc chloride of 
specific gravity 1.8. The viscous mass so 
obtained is then forced or squirted under 
pressure through a die of suitable diameter 



PREPARATION OF THE FILAMENT. 89 

into a vessel containing alcohol, which 
causes a hardening of the filament. If 
this process is properly carried on it pro- 
duces a filament of uniform cross-sectional 
area, so as to dispense with the necessity 
for passing the thread through shaving 
dies. Care has to be taken to avoid the 
formation of air bubbles in the viscous 
mass, which would either result in a break- 
ing of the thread, or in a lack of homo- 
geneity of the filament. This process is 
now in very extensive use. 

Another process has been invented for 
the production of an artificial material 
suitable for cutting or shaping into fila'ments 
for incandescent lamps, and subsequent car- 
bonization. This process consists essen- 
.tially in converting cellulose, obtained from 
cotton, into a substance known as pyroxy- 
liue,.,or gun-cotton, whence it is converted 



90 ELECTRIC INCANDESCENT LIGHTING. 

into celluloid. The celluloid is rolled into 
thin sheets. The sheets in this condition 
are not yet fit to be subjected to the car- 
bonizing process, and must first be again 
converted into cellulose. This change is 
effected by treating them with am- 
monium sulphide, which produces struc- 
tureless, cellulose sheets. These are then 
treated with bisulphide of carbon, or tur- 
pentine, to remove all traces of sulphur, 
and are then ready to be cut or shaped 
into filaments and carbonized. 

The filaments so cut or shaped by 
the preceding processes, must be sub- 
jected to a carbonizing process. During 
carbonization a number of changes occur 
in the filament. In the first place the 
filament becomes hard and brittle, and, 
to a certain extent, acquires a definite 
shape or form, so that it is necessary be- 



PROPERTY CF 

91 




PREPARATION 

fore carbonizing it 
which it is to permanently retain. In 
the next place the filament shrinks per- 
ceptibly during carbonization, so that 
means must be devised for permitting 
this shrinking to take place without 
rupture. 

The means employed for the carboniza- 
tion of the filament, will vary with the 
shape and character of the material of 
which it is made. The degree and dura- 
tion of the heat employed in carbonization 
will also vary with the character and 
method of preparation of the material. 
It will, therefore, be necessary briefly to 
describe the methods employed for the 
carbonization of particular characters of 
filaments. In this connection, however, 
it must be remarked that the manufac- 
ture of the incandescent lamp, as it is 



92 ELECTRIC INCANDESCENT LIGHTING. 

carried out to-day, is, to a great extent, 
a secret process. Therefore, such descrip- 
tions must necessarily be limited to 
known processes which have been tried 
and which have been found successful in 
practice. 

In the case of the bamboo filaments, the 
material, shaped as already described, is 
placed in a suitable box or receptacle 
formed of carbon, or other refractory sub- 
stance, under such conditions that the fila- 
ment shall be permitted to contract freely 
while being subjected to a constant and 
even tension. In Fig. 11, such a box is 
shown with the filaments to be carbonized 
placed in position. This box is in two 
parts as shown, an outer air-tight chamber, 
and an inner forming plate. The fila- 
ments to be carbonized are placed in the 
inner groove around the block E II, with 



PREPARATION OF THE FILAMENT. 



93 



their extremities secured beneath the 
bridge piece a h, which is fixed in an 
outer frame. As the filaments contract 




FIG. 11. CARBONIZING Box. 

during the process, since they cannot 
draw up into the groove from the bridge, 
they pull the whole block EH, forward 
under the bridge, and so maintain a steady 



94 ELECTRIC INCANDESCENT LIGHTING. 

and uniform tension upon the filaments. 
A suitable cover, provided with a flange 
fitting into the outer groove, is placed on 
the box. A number of such boxes are 
packed together into a suitably closed flask 
which is placed in the carbonizing furnace. 

When the filaments to be carbonized 
are prepared from cotton thread, by the 
process already described, owing to the 
pliability of the material, it is necessary 
to give it the required shape before it is 
set or hardened during carbonization. 
This is accomplished by winding the 
thread on a suitable block or form. As 
in the case of the bamboo filament, means 
must be provided for allowing shrinkage 
to take place. This is accomplished by 
means of a carbonizing frame, which con- 
sists essentially of a suitably shaped block 
and an end piece of carbon, connected to- 



PREPARATION OF THE FILAMENT. 95 

gether by sticks of wood. These sticks 
are firmly fixed to the end piece and 
pass loosely into openings in the main 
block which rests on them. The threads 
to be carbonized, are wrapped tightly 
around the block and end piece, which 
is so placed in the carbonizing box that 
on the shrinkage of the thread, the 
wooden sticks, whose dimensions have 
been carefully selected, shrink to the same 
extent, thus permitting the upper block to 
slowly descend on to the end piece. A 
number of such frames are packed to- 
gether in a carbon box, which is itself 
placed in a crucible. The space between 
box and crucible is filled with powdered 
carbon. 

In the carbonization of amyloid threads, 
it has been found that in order to obtain 
the best results, the heat must be very 



96 ELECTRIC INCANDESCENT LIGHTING. 

gradually applied. Should the crucibles 
be exposed to a sudden increase of tem- 
perature, the filament contracting too 
suddenly, may be broken. Moreover, the 
gases produced by distillation might possi- 
bly deposit sufficient carbon on the sides 
of the filaments, to interfere with their 
homogeneity and also to cause them to 
cohere. Consequently, a pyrometer is fre- 
quently used in connection with the 
furnace in order to regulate its tem- 
perature. The time required to effect the 
carbonization will vary with the size and 
character of the filaments. Ordinary 
thread filameuts may require eighteen 
hours for their proper carbonization, al- 
though a longer time may be employed. 
The period required for carbonization, 
necessarily varies with the size of the fila- 
ments, their character and the nature of 
the furnace. 



PREPARATION OF THE FILAMENT. 97 

Incandescent lamp filaments are now 
sometimes manufactured by a squirting 
process. This is in the main a secret 
process, but it consists essentially in ob- 
taining an exceedingly intimate mixture 
of carbonaceous materials, forming them 
into a plastic mass and subjecting the 
same, while in the plastic condition, to 
powerful pressure, whereby they are forced 
or squirted through molds in die plates. 
Means are devised for preserving the shape 
which it is desired that this material 
should take, and then, after carefully dry- 
ing the same, it is submitted to a suitable 
carbonizing process. Experience has shown 
that squirted filaments are capable of being 
rendered perfectly uniform. In all cases 
after the filaments have received the proper 
carbonization, it is necessary to wait until 
the furnace and its contents are cooled, 
before removing them from the carboniz- 



98 ELECTRIC INCANDESCENT LIGHTING. 

ing boxes, both on account of their fragile 
character, and for the sake of the furnace, 
which is apt to be injured by the sudden 
chilling. 



CHAPTER VI. 

MOUNTING AND TREATMENT OF FILAMENTS. 

HAVING traced the filaments up to the 
completion of their carbonization, we will 
assume that they are ready to be removed 
from the carbonizing box. As already 
stated, the box and its contents are sup- 
posed to have cooled down to the tem- 
perature of the room. Care must be exer- 
cised in removing the filaments from the 
box, since the carbonization has changed 
the physical nature of the material, and the 
carbons are now brittle, though hard and 
elastic. 

The next step in the manufacture of the 
lamp now begins viz., the mounting of 



00 



100 ELECTRIC INCANDESCENT LIGHTING. 

the filament, or placing it upon a glass sup- 
port through which the leading-in wires, 
or the conductors which carry the current 
to the filament are sealed. The ends of 
the filament are attached to the extremi- 
ties of the leading-iu wires by any suitable 
means. Much ingenuity has been dis- 
played in obtaining a suitable mounting 
for the filament, and for a long time this 
mounting constituted the weak- point in 
the lamp. Any collection of incandescent 
lamps, embracing specimens from an early 
period in the history of the art, would show 
how marked the evolution has been in this 
particular. 

In order to obtain an idea of the rela- 
tion of the various parts of the mounted 
filaments reference may be had to Fig. 12, 
which shows one of the common forms of 
mounting. A glass tube T, has a shoul- 



TREATMENT OF FILAMENTS. 



101 



der blown on it at 8. Two copper wires 
MI, w 2) ordinarily 0.015" in diameter, are 
welded to short pieces of platinum wire, 



\ w t 
FIG. 12. THE MOUNTED FILAMENT. 

the method generally adopted being to 
hold the end of the copper wire against 
the end of the platinum wire in a flame, 
when they fuse together. These two 



102 ELECTRIC INCANDESCENT LIGHTING. 

wires constitute the leading-in wires. 
These wires are then laid in the glass 
tube T, and the glass is fused around the 
platinum wires in a flat seal at the point 
/SJ so that short projections of the plati- 
num p, p, extend through the glass seal. 
The glass seal is then carefully annealed. 
The filament f, is now connected with its 
ends to the wires p, p. 

When it is remembered that the opera- 
tion of an electric lamp necessarily brings 
the filament to a white heat, it will be evi- 
dent that means must be provided either 
for preventing the joints at p, p, from 
attaining a high temperature ; or, if such 
temperature be attained, that the character 
of the joint must be such that it will not 
suffer. In any event it is clear that the 
seal S 9 must not be exposed to an incan- 
descent temperature, and, therefore, the 



TREATMENT OF FILAMENTS. 103 

platinum extremities p, p, must remain 
comparatively cool. The method which 
is always adopted is to provide such a 
cross section at the joints p, p, that, taken 
in connection with the thermal conductiv- 
ity of the platinum wires, the tempera- 
ture of the joints will be much below the 
incandescing temperature of the rest of the 
filament. In the earlier forms of lamps, 
in which very large currents were usually 
employed, this result was accomplished by 
providing massive terminals connected 
with the carbon filament, possessing so 
great a radiating surface that their tem- 
perature was necessarily, comparatively 
low. Moreover, since most of these early 
forms of lamps did not employ a solid 
glass seal, it was still further necessary 
to reduce the temperature of the leading- 
in wires at the points of entry by means 
of cement. 



104 ELECTRIC INCANDESCENT LIGHTING. 

Platinum is employed where the glass 
is fused around the leading-IB wires, for 




FIG. 13. HORSESHOE LAMP. 



the reason that the expansion and con- 
traction of platinum is almost the same 



TREATMENT OF FILAMENTS. 105 

as that of glass. The expansion of glass 
rods varies from 0.0007 to 0.001 per cent, 
of their length, for each degree Centigrade, 
or just about the mean value of the 
expansion of platinum wires. When, 
therefore, glass is sealed around a plat- 
inum wire, and the seal is heated, the 
glass and the platinum expand together, 
and, on cooling contract together. If 
this were not the case, there would be 
a continual tendency to shear the glass 
over the platinum surface, and break 
the seal both on expansion and con- 
traction. Among ordinary metals iron 
comes next to platinum as regards its 
expansion, and iron has been employed to 
some extent for the seal in incandescent 
lamps. 

Fig. 13, represents an early form of 
lamp in which this method of connection 



106 ELECTRIC INCANDESCENT LIGHTING. 

was employed. A filament is connected 
to large terminals of copper supported on 
an insulating bridge. These terminals are 
further connected with long zig-zag strips 
of copper, extending to the base of the 
lamp, for the purpose of ensuring a low 
temperature where they pass through the 
base. 

In some of the earlier lamps of the 
modern type the ends of the filaments 
were made of enlarged cross section, so that 
they were not only more readily secured 
to the platinum leading-in wires, but also 
by their increased mass prevented the cur- 
rent from raising it to the temperature of 
incandescence. In Fig. 14, a filament of 
bamboo is provided with enlarged ends. 
In some cases the carbon filaments, after 
they had been subjected to the carboniz- 
ing process, and while still in place in 



TREATMENT OF FILAMENTS. 107 

the carbonizing box, had their ends thick- 
ened by deposits of carbon, produced from 



FIG. 14. BAMBOO FILAMENT. 



108 ELECTRIC INCANDESCENT LIGHTING. 

the decomposition of a- carbonizable gas, 
forced into the mold at a certain stage 
in the process. 

A very early form of joint consisted of 
a platinum bolt and nut, as shown in 
Fig. 13. A small screw lamp was some- 
times employed for the same purpose as 
shown in Fig. 15. At one time, small 
metal blocks, O, C, were employed 
fastened upon the enlarged extremities of 
the filament, as shown in Fig. 16. Some- 
times a small socket was formed in the 
end of the wire, and the carbon was 
placed in this receptacle and the socket 
pressed around it. In another form, the 
socket joint was secured more firmly to 
the carbon by covering it with an elec- 
trolytic coating of carbon, or the wire was 
wrapped around the carbon and subse- 
quently secured to it in the same manner. 



TREATMENT OF FILAMENTS. 109 




FIG. 15. EARLY FORM OP JOINT LAMP. 



110 ELECTRIC INCANDESCENT LIGHTING. 

This proved an excellent form of joint, 
and was employed extensively for a num- 




FIQ. 16. EARLY FORM OF CLAMP. 




TREATMENT OF I fc^ AMENTA 'PL fil^Y , f 

ber of years. It has, n^^er, been re- 
placed by a still simpler r^gcln^wbich ' 
no socket is employed, but one en3ToT"t1ie 
filament is abutted against the end of the 
platinum wire, and carbon is deposited 
around the joint. This joint is obtained 
by dipping the abutting end into a suit- 
able carbonizable liquid and sending a 
powerful current through the abutment 
w T hile in the liquid. Under these con- 
ditions, a decomposition of the liquid 
occurs and hard carbon is deposited 
on the joint, thus effecting a thorough 
seal. At the present time the still simpler 
method is usually adopted of cementing 
the two together by a lump of carbon 
paste or dough. 

In the early history of the modern in- 
candescent lamp, the filaments, produced 
by substantially the processes already de- 



112 ELECTRIC INCANDESCENT LIGHTING. 

scribed, when placed in the exhausted 
lamp chamber and rendered incandescent 
by the passage of a current through them, 
were frequently found to glow irregularly, 
that is to say, there were parts w T hich were 
rendered vividly incandescent while other 
parts were only dull red. This was due 
to the fact that the process did not pro- 
duce homogeneous carbon filaments. In 
other words, either the diameter varied at 
different parts, or the resistivity of the 
material varied, or both. Consequently, 
when the incandescing current was sent 
through the filament, and the temperature 
gradually increased, the high resistance 
parts of the filament first began to glow, 
while the others remained comparatively 
cool, the heat being developed by the cur- 
rent in proportion to the resistance en- 
countered. If such a spotted filament 
were employed in the lamp and the tern- 



TREATMENT OF FILAMENTS. 113 

perature raised by increasing the cur- 
rent, so as to make all parts of the fila- 
ment glow, then the temperature of the 
high resistance portions would probably 
be raised beyond the limit of safety 
and the life of the lamp would conse- 
quently be much shortened ; while, on the 
contrary, if the higher resistance portions 
of the filament w r ere limited to the safe 
temperature, the lower resistance portions 
would be at so low a temperature, that the 
candle-power of the entire lamp would be 
unduly low. 

This difficulty was happily overcome by 
an exceedingly ingenious process, gener- 
ally called the flashing process, which 
consisted essentially in a means whereby 
carbon was caused to be deposited only 
upon those portions of the filaments whose 
resistance was higher than the rest. In 



114 ELECTRIC INCANDESCENT LIGHTING. 

other words, if the filament were unduly 
narrow at some particular spot, or had an 
undue resistivity at such spot, then carbon 
would be deposited upon this spot only. 

The flashing process is carried on sub- 
stantially as follows. The mounted fila- 
ment is placed in a suitable chamber from 
which the air has been removed, and 
which is subsequently filled with a hydro- 
carbon vapor. An electric current, whose 
strength is gradually increased, is then 
sent through the filament. A hydro- 
carbon gas or vapor, suffers decomposition 
in the presence of a heated surface as soon 
as a certain temperature is reached. As 
the current gradually increases, the carbon 
filament begins to glow at its point of 
greatest resistance, and this point, conse- 
quently, receives a deposit of carbon, thus 
decreasing the resistance locally. If this 



TREATMENT OF FILAMENTS. 115 

current strength were maintained, the car- 
bon would cease to glow at these points. 
If, however, the current strength be fur- 
ther increased, the carbon would begin to 
glow at the point of next highest resist- 
ance, and this in turn, receiving a deposit, 
would cease to glow at this current 
strength. It will be readily seen, there- 
fore, that as the current strength is gradu- 
ally increased, the filament receives a 
deposit at those portions of its mass only 
where it needs increase in conducting 
power, and soon the entire filament will 
glow with a uniform intensity of light. 

It must not be supposed, that the car- 
bon is now absolutely of the same area 
of cross section, or of the same thickness 
throughout. The flashing process has 
rendered it electrically, but not mechani- 
cally, homogeneous. We have correctly 



116 ELECTRIC INCANDESCENT LIGHTING. 

described the process as consisting of suc- 
cessive steps reached by gradually increas- 
ing the current strength. In point of fact, 
these steps follow one another so rapidly 
that the process at first sight may seem 
to be almost instantaneous, only a few 
seconds being required for an exceedingly 
spotted carbon to emit a uniform glow. 

Although at the present day improve- 
ments in manufacture have resulted in the 
production of filaments, which are so 
nearly uniform in their resistance that 
they will glow uniformly when placed in 
the lamp, and, therefore, do not require 
to be subjected to the flashing process, 
nevertheless, since this process results in 
giving to the filament other valuable prop- 
erties, it is still generally practiced. Not 
only are the surfaces of flashed carbon 
filaments harder than those which have not 



TREATMENT OF FILAMENTS. 117 

undergone tins process, but the amount of 
liglit which they emit for a given current 
strength is markedly increased. 

The flashing process is sometimes 
carried on in liquids, such as beuzine, the 
filaments being dipped in the liquid and 
the current, as before, supplied in gradu- 
ally increasing strength. In such cases, 
however, the decomposition of the liquid 
produces an atmosphere of gas around 
the filament so that the difference in the 
process is rather in appearance than in 
reality. 



CHAPTER VII. 

SEALING-IN AND EXHAUSTION. 

THE mounted and flashed filament has 
now to be inserted in an enclosing glass 
chamber, in which it is hermetically sealed. 
This sealing- in, is preferably accomplished 
by the actual fusion of the glass stem to 
the lower part of the globe. It will be 
interesting, therefore, to examine in detail 
the method generally employed in the 
manufacture of the incandescent lamp 
chamber and its hermetical closure on 
sealing-in. 

Fig. 17, represents the successive steps 
that are generally taken in the sealing-in 

118 



SEALING-IN AND EXHAUSTION. 



119 



of the mounted filament in the lamp 
chamber. The glass lamp chamber A, 




FIG. 17. STEPS OP SEALING-IN PROCESS. 

has the form shown, the open tubular pro- 
jection being left at , for the exhaustion 
of the chamber. The open end of the 



120 ELECTRIC INCANDESCENT LIGHTING. 

chamber A, is of such dimensions that the 
mounted filament can be introduced into 
it up to the shoulder d, which then rests 
in contact with the lower end a, of the 
chamber. The stem is then grasped by 
the glass-blower in one hand, and the 
tubular end of the chamber in the other, 
and the two revolved together as one 
piece, in a suitable blow-pipe flame di- 
rected upon the shoulder or joint, until 
the fusing temperature is reached, and the 
edge a, becomes hermetically sealed with 
the shoulder d. By this means it will be 
seen that an enclosing chamber, made en- 
tirely of glass, is provided with leading-in 
wires passing through the support at />, p. 
In the early history of the art, it was 
necessary that this delicate operation 
should be performed by a skilled glass- 
blower, but during recent years, machines 
have been introduced which grasp the 



SEALING-IN AND EXHAUSTION. 

globe aud stein and revolve them in the 
blow-pipe flame with the requisite amount 
of pressure. The machine seal, so ef- 
fected, is made as swiftly and neatly as 
that of the most expert workman. The 
sealed-in lamp is then carefully annealed, 
by subjecting it to the action of a gradu- 
ally diminished heat, while under the 
action of a roller. Great care is neces- 
sary that the annealing of the joint should 
be thoroughly effected. 

Attempts have been made, at different 
times, to produce a lamp in which a 'me- 
chanical seal was effected between the 
stem and the globe, instead of a seal by 
fusion. Such a seal possesses the advant- 
age of permitting the lamp to be readily 
repaired on the breaking of the filament. 
Figs. 18, 19, and 20, show a form of Kich 
stopper-lamp, as it is generally called. 



122 ELECTRIC INCANDESCENT LIGHTING. 



Fig. 18, represents the mounted filament, 
which is connected to the extremities of 
two iron wires sealed into the neck or 




FIG. 18. STOPPER-MOUNTED FILAMENT OF INCAN- 
DESCENT LAMP. 

stem L. We have already pointed out 
that iron is sometimes employed for this 
purpose. The stopper portion of the stem 



SEALING-IN AND EXHAUSTION. 123 

at /SJ is ground by machinery to fit a simi- 
larly ground seat in the opening of the 
lamp globe, which is shown at A, Fig. 19. 
The mounted filament is inserted into the 
lamp chamber, and the stopper secured in 
its seat by a flexible cement. A brass 
shell is then secured around the base B of 
the lamp, enabling connections to be main- 
tained with its terminals, as shown in 
Fig. 20. 

The mounted filament, having thus been 
introduced into the lamp chamber, and the 
base of the lamp hermetically sealed, the 
next step is the exhaustion of the lamp 
chamber. An exceedingly small quantity 
of air left in the chamber will contain 
sufficient oxygen to cause rapid destruction 
of the lamp filament. Consequently, it is 
necessary to remove, as far as possible, all 
traces of air from the interior. This is 



124 ELECTRIC INCANDESCENT LIGHTING, 




FIG. 19. GLOBE OF STOPPER LAMP. 



SEALING-IN AND EXHAUSTION. 125 

accomplished by means of pumps. The 
ordinary mechanical air-pump, of the auto- 
matic valve type ; i. e., in which the 
valves are opened and closed automatically 
by the motion of the piston, is capable 
of producing fairly high vacua, but not 
sufficiently high for the purposes of being 
used alone in the exhaustion of the lamps, 
since the residual air would still be detri- 
mental. Mechanical pumps, however, are 
often used for producing a rapid exhaus- 
tion of the lamp chamber, the final exhaus- 
tion being accomplished by means of a 
mercury pump. The operation of the mer- 
cury pump, however, is so simple in practice 
and efficient in action, that in some cases, the 
use of the mechanical pump is dispensed 
with, and the entire process of exhaustion 
is carried on by the mercury pump alone. 

A great variety of mercury pumps have 



126 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 20. COMPLETED STOPPER LAMP. 







PROPERTY 

SEALING-IN ANJ^xJ^QIAUSTION. 127 




been devised, all of 
niently divided into two classes"? 1 
those of the Geissler type, in which the 
vacuum is obtained by utilizing the prin- 
ciple of the so-called Torricellian vacuum, 
of the barometer tube, and those of the 
Sprengel type, in which the vacuum is 
obtained by the fall of a stream of mer- 
cury. When a column of mercury is per- 
mitted to fall through a vertical tube, 
connected near its upper end by a branch 
tube with the chamber to be exhausted, 
the air will be carried away from the 
chamber by becoming entangled as bub- 
bles in the falling column. Mercury 
pumps of this character are well adapted 
to the exhaustion of lamps, owing to the 
simplicity and efficiency of their action. 

When the proper degree of vacuum is 
obtained, the lamp is sealed-off by fusing 



128 ELECTRIC INCANDESCENT LIGHTING. 

the tube at tlie top of the lamp chamber, 
with a blow-pipe flame, a constriction being 
provided in the tubulure I, at & 1 as shown 
in Fig. 17, for facilitating this process. 
In the early state of the art this sealing-off 
was effected while both the lamp and the 
filament were cold. It was found, when 
thus sealed-off, that, although the proper 
vacuum had been obtained, and the lamp 
operated satisfactorily for a while, yet the 
vacuum soon invariably deteriorated, so 
that the life of the lamp was unduly short- 
ened. The explanation was at last found 
in the fact that gases were occluded or 
absorbed in the carbon filament, as well as 
condensed on the inner surface of the globe. 
These gases adhered to the filament, or to 
the globe, with too great a force to per- 
mit them to escape into the lamp chamber 
during the process of exhaustion. When, 
however, the lamp was lighted after con- 



SEALING-IN AND EXHAUSTION. 129 

eluding the process of exhaustion, the in- 
tense heat of the filament disengaged 
these gases which reduced the vacuum in- 
juriously. The remedy is simple. As 
soon as a fairly good vacuum is obtained 
in the lamp, an electric current is sent 
through the filament and the last stages of 
the pumping process are carried on while 
the filament is aglow. Immediately be- 
fore sealing-off, the current is increased 
beyond the strength intended to be em- 
ployed in practice, and the lamps sealed 
while the pumping is carried on. By this 
means the occluded gases in the filament 
and on the globe are carried off, and this 
process has done much to improve the lamp. 

When incandescent lamps were first 
manufactured on a large scale, an effort 
was made to obtain as high a. vacuum as 
possible, and pumps were employed which, 



130 ELECTRIC INCANDESCENT LIGHTING. 

it was claimed, left a residual atmosphere 
in the lamp chamber of but 1,000,000th of 
its original amount; that is that 999,999 
parts of air out of every million had been 
removed. Even at the present time, while 
it is generally considered that residual 
atmospheres of air, containing as they 
necessarily must traces of oxygen, result in 
a decreased life of the lamp, yet it may be 
asserted, as a result of actual experience, 
that residual atmospheres of certain gases, 
such as chlorine or bromine, or mixtures 
of the same, may not only be innocuous 
but actually advantageous. 

It is quite possible, during the opera- 
tion of a lamp, the sealing-off of which 
has been thoroughly made, that the vacuum 
may actually improve rather than dete- 
riorate ; for, in the disintegration of the 
carbon, to which we shall allude in a sub- 



SEALING-IN AND EXHAUSTION. 131 

sequent chapter, a deposit of finely divided 
carbon takes place inside the lamp cham- 
ber. This carbon possessing, as it does, 
the power of occluding or absorbing resid- 
ual atmospheres, would naturally tend to 
improve the vacuum during use. 

The exhausted and sealed lamp must 
now be provided with a base, whereby it 
can be readily placed in a socket or sup- 
port. The lamp base is so arranged that 
two metallic portions, suitably insulated 
from one another, are connected to the 
ends of the leading-in wires. These por- 
tions on the base are adapted to connect 
the lamp with the circuit wires by the 
mere act of placing it in the lamp socket. 
Various forms of lamp bases are employed 
as we shall see hereafter. The lamp base 
is attached to the lamp by a cement, gen- 
erally of plaster of Paris. 



132 ELECTRIC INCANDESCENT LIGHTING-. 

Some of the more usual forms of lamp 
bases are shown in Fig. 21 at A, B, C 
and D. The two separate metallic pieces, 
which are electrically connected to the 
ends of the leading-in wires, are, in all 







FIG. 21. LAMP BASES. 

cases, indicated by the letters a and Z>. 
An inspection of the figure will show that 
A^ has a central contact pin as one termi- 
nal, and a concentric brass ring as the 
other terminal. B, has a central pin as 
one terminal, and an external concentric 
cylinder as the other. At (7, two concen- 
tric cylinders are employed, the inner one 
has, however, a screw thread for securing 
it in its socket. D, has a screw shell as 



SEALING-IN AND EXHAUSTION. 133 

one terminal, and a central cap as the 
other terminal. 



It is sometimes convenient to fit a lamp 
of one manufacture into a socket of 




FIG. 22. LAMP ADAPTERS. 



another manufacture. For this purpose a 
device called a lamp adapter is employed. 
An adapter consists essentially of an exte- 
rior base and an interior connection piece. 



134 ELECTRIC INCANDESCENT LIGHTING. 

In Fig. 22, four adapters are shown suit- 
able for attachment to a stopper lamp, and 
provided with bases corresponding to the 
lamp bases shown in A, B, C\ D, of Fig. 
21, similar letters corresponding in the 
two figures. The use of stopper lamps has, 
however, been abandoned. 




CHAPTER VIII. 

LAMP FITTINGS. 

the removal of the lamp from the 
pumps, it is tested for candle-power, and 
marked in volts for the pressure which 
should be supplied to it in operation. 

Some examples of finished lamps are 
shown in Fig. 23. These lamps are all of 
the same type and differ only in the form 
of base. The bases of these lamps differ 
so as to permit each lamp to be used on 
some particular socket. 

One of the simplest forms of sockets 
intended for inexpensive work, especially 



135 



136 ELECTRIC INCANDESCENT LIGHTING. 







FIG. 23. COMPLETED INCANDESCENT LAMPS. 



LAMP FITTINGS. 



137 



where the lamps are not open to direct ob- 
servation, such as at the foot or side lights 
of theatres, is shown in Fig. 24. This 




FIG. 24. SIMPLE FORM OP SOCKET. 

socket is intended to receive a lamp with a 
screw base. A wooden shell Z, is screwed 
to the wall or other support, by ordinary 
screws passing through the screw holes, 
one of which is seen at S. A and ^?, are 
brass screws intended for the reception of 



138 ELECTRIC INCANDESCENT LIGHTING. 

the circuit wires or mains, and are con- 
nected respectively to the brass screw shell 




FIG. 25. KEYLESS WALL-SOCKET. 

(7, and a central cap beneath. These will 
make contact with the two insulated por- 



LAMP FITTINGS. 139 

tions of the base of the lamp when the 
lamp is screwed in. 




FIG. 26. KEY WALL-SOCKET. 

Fig. 25, shows a more sightly form of 
keyless socket, that is, a socket which is not 



140 ELECTKIC INCANDESCENT LIGHTING. 

provided with a key or switch, and which, 
therefore, constantly maintains connection 
between the mains and the lamp. The 
base 13 J?, is of porcelain, and is fixed in 
position by screws passing through screw 
holes C\ C. Supply wires, connected with 
the mains, pass beneath through the 
grooves W, W. Connections are main- 
tained through the interior of the shell. 

A socket of a similar character, but pro- 
vided with a key K, is shown in Fig. 26. 
In this case the lamp is lighted or extin- 
guished by the turning of the key. In 
the case of keyless sockets the lamps are 
turned on or off by the action of a distant 
switch. 

Socket keys, open and close the circuit of 
a lamp at one point in a variety of ways. 
Two forms of socket keys are shown in 



LAMP FITTINGS. 



141 



Figs. 27 and 28. Fig. 27, shows a socket 
suitable for use with a lamp base of type 
B, Fig. 21; and Fig. 28, shows a socket 
suitable for use with the lamp base of type 




PIG. 27. DETAILS OP SOCKET. 

Oj in that figure. In Fig. 27, the turning 
of the key K, makes contact between the 
brass segments b, Z>, through the interme- 
diary of the cam, on the extremity of the 
key axis. In Fig. 28, a similar method is 



142 ELECTRIC INCANDESCENT LIGHTING. 

employed. Here the movement of the 
key closes connection between contacts 
by ^ through the metal piece C. 




FIG. 28. DETAILS OP LAMP SOCKET. 

Fig. 29, represents in cross-section a 
lamp with a screw base in its socket. 
The current is turned on or off at the key 
K. 6r, is the globe, and T, the tip at which 
the lamp was sealed on removal from the 
pump ; Pj is the filament ; 8 9 the seal of 
the leading-in wires ; W, the welds be- 
tween the platinum and the copper lead- 



" 




JP 

FIG. 29. LAMP AND SOCKET SHOWING CONNECTIONS. 



144 ELECTRIC INCANDESCENT LIGHTING. 

ing-in wires; $', the seal of the lamp stem 
with the glass chamber. Z, Z, are projec- 
tions of the glass on the surface of the 
shoulder, intended to aid in securing the 

/ o 

lamp in its plaster of Paris cement. 6 Y and 
12, are the cap and screw metallic pieces of 
the base, each in soldered connection with 
one leading-in wire as shown. A and J3, 
are the cap and screw connections of the 
socket, each in connection with one of the 
external wires entering the socket through 
the pipe or metallic support P. One of 
these wires is connected directly with the 
brass shell A, while the other is connected 
with the cap />, only through the interme- 
diary of the key K. M M, is the external 
brass shell of the socket, insulated from 
the interior portions by the hard rubber 
ring n n. 

When an incandescent lamp is supported 



LAMP FITTINGS. 



145 



by a flexible cord, it usually requires both 
hands to turn the key at the socket on or 
off, one to hold the lamp, and the other to 




FIG. 30. Pusn BUTTON KEY SOCKET. 

turn the key. Fig. 30, shows a device by 
which the turning on or off can be accom- 
plished by the hand which holds the 



146 ELECTRIC INCANDESCENT LIGHTING. 

socket. This is accomplished in replacing 
the ordinary key by two pressure buttons. 
Pressure upon the stud A J forces it home 
until it is locked by the trigger B, thus 




PIG. 31. SPRING SOCKET FOR SCREW BASE. 

turning on the lamp and keeping it turned 
on. Pressure on the trigger B, releases 
the push A., which returns to its original 
position under the action of a spring. 

Fig. 31, shows a form of spring socket for 
a screw lamp base. For temporary work, 



LAMP FITTINGS. 



147 



such as exhibitions, etc., where the expense 
of permanent fixtures would not be justi- 
fied, a temporary socket is sometimes em- 
ployed, as shown in Fig. 32. It consists of 




FIG. 32. TEMPORARY SOCKETS. 

a spiral spring holding the screw base of 
the lamp, and connected with one supply 
wire W, while the brass screw in the centre 
of the spiral is connected with a second 
supply wire beneath the wooden base bar 



148 ELECTRIC INCANDESCENT LIGHTING. 

Such construction is, of course, not re- 
garded as safe for permanent use in 
buildings. 

Where lamps are placed in positions 
exposed to the weather, it is necessary to 




FIG. 33. WEATHER-PROOF SOCKETS. 

employ some form of weather-proof socket. 
Two forms of such sockets in common use 
are shown in Fig. 33, that on the right hand 
side being of glass, and that on the left, 



LAMP FITTINGS. 149 

of hard rubber or composition. These 
sockets are intended for the reception of 
screw bases. 

Various forms of reflecting surfaces are 
employed in connection with the lamps so 




FIG. 34. METALLIC SHADE FOB REFLECTING LIGHT 
DOWNWARDS. 

as to throw the light in any desired direc- 
tion. Two such forms of lamp shades, 
devised to throw the light downwards, 



150 ELECTRIC INCANDESCENT LIGHTING. 

are shown in Figs. 34 and 35. The depth 
of the shade will vary with the character 
of the illumination required. That shown 
in Fig. 34, is suitable for the illumination 
of desks from above. Fig. 35, is suitable 




FIG. 35. METALLIC SHADE FOR REFLECTING LIGHT 
DOWNWARDS. 



for the illumination of a billiard table. 
Fig. 36, shows a form of half shade some- 
times employed for desk use. Here one 
half of the lamp only is covered by the 



LAMP FITTINGS. 151 

shade which in outline conforms with the 
shape of the lamp, the inside of the shade 
being provided with a good reflecting sur- 
face to throw the light downwards. 




FIG. 36. METAL HALF SHADE FOR DESK USE. 

It is important in order to ensure 
good illumination for reading, that all 
portions of the printed page shall be 
equally lighted. Although this is gener- 



152 ELECTRIC INCANDESCENT LIGHTING. 

ally secured by the aid of aiiy good shade, 
yet it is often preferable to employ for 
this purpose the form of shade and en- 
closing globe shown in Fig. 37. 




FIG. 37. REFLECTOR SHADE. 

i Instead of forming the lamp shade out 
of a single surface, a number of sur- 
faces are sometimes employed, either plane 
or curved. Figs. 38 and 39 represent 



LAMP FITTINGS. 153 

panel reflectors j i. e., reflectors composed of 
strips or panels of silvered glass. These 




FIG. 38. CONCAVE PANEL SHADE AND REFLECTOR. 

reflectors are suitable for store windows or 
railway stations. The shade in Fig. 38, 
is designed to throw light downwards from 




FIG. 39. CONCAVE PANEL SHADE AND REFLECTOR. 



154 ELECTRIC INCANDESCENT LIGHTING. 

its concave surface, and Fig. 39 to throw 
the light outwards from its convex surface 
as well as downwards. Finally, reflectors 
of similar forms are also arranged to oper- 




FIG. 40. PANEL REFLECTOR AND SHADE FOR CLUSTER. 

ate with clusters of lights to illumine 
larger halls. A concave panel reflector of 
this type is shown in Fig. 40. 

Sometimes corrugated silvered glass is 
employed in various forms for reflecting 



LAMP FITTINGS. 155 

purposes. Fig 41, shows a reflector of 
this type made in the form of a shade. 




FIG. 41. CORRUGATED REFLECTOR AND SHADE. 

Even transparent or translucent sub- 
stances may at times be employed for 
reflectors. In such cases they aid in 
scattering light downwards as well as in 



156 JflLKCTKIO INCANDESCENT LIGHTING. 

reflecting it. Materials employed for this 
purpose are glass and porcelain, either 
plain or corrugated, transparent or trans- 




FIG. 42. GLASS SHADES. 

lucent. Fig, 42, shows a variety of shades 
employed for such purposes. 

Owing to the fragile nature of the in- 
candescent lamp chamber, it is necessary, 



LAMP FITTINGS. 



157 



when lamps are placed in exposed posi- 
tions, to protect them from accidental 
destruction by blows. For this purpose 
wire gratings or shields are arranged, of 




FIG. 43. HALF WIRE-GUARD. 

such form and outline as shall not seriously 
interfere with the light. Such grat- 
ings would, of course, be inadmissible in 
any situation where marked shadows 



158 ELECTRIC INCANDESCENT LIGHTING. 

are objectionable, and should, therefore, 
only be employed in cellars, underground 
passages, or in similar situations. Fig. 43, 
shows a form of half wire-guard, which, 




FlG. 44. FCLL, WlRE-GUAKD. 

as its name indicates, only surrounds 
a portion of the lamp proper. Fig. 44, 
shows a full wire-guard surrounding the 
entire lamp. In Figs. 45 and 46, some 



LAMP FITTINGS. 159 

forms of wire-guards are shown, suitable 

O ' 

for portable or hanging lamps. 

Sometimes, instead of employing a wire 
guard to protect the lamp, the lamp is 





FIG. 45. WiRE-GuAKDS FOR SUSPENDED LAMPS. 

entirely surrounded by an air-tight or 
a steam-tight glass lamp chamber as in 
Fig. 47. This globe consists of two parts, 
a cylindrical glass cover with a rounded 



160 ELECTRIC INCANDESCENT LIGHTING. 

end, provided with a screw thread metallic 
cap, capable of tightly fitting into the base 





FIG. 46. PORTABLE LAMP GUARD. 

as shown. A steam-tight lamp chamber is 
employed under circumstances where it is 
either desired to protect the lamp from cor- 



LAMP FITTINGS. 



161 




FIG. 47. STEAM-TIGHT LAMP CHAMBER. 

rosive vapors, from spray at sea, or for the 
purpose of avoiding any possible accident 
which might result, from the explosion of 



162 ELECTRIC INCANDESCENT LIGHTING. 

inflammable gases or clouds of dust, on the 
accidental breaking of the lamp chamber 
and globe. It will, of course, be under- 
stood that the use of any form of wire 
grating, or steam-tight globe, must neces- 
sarily be attended by a marked decrease in 
the useful illumination of the lamp. 



CHAPTER IX. 

THE INCANDESCING LAMP. 

WE have now traced the manufacture of 
the lamp up to the time when it is ready 
to be connected with the supply wires and 
actuated by the electric current. With this 
the manufacture of the incandescent lamp, 
that is a lamp capable of being rendered 
incandescent, now ceases, and the story of 
the incandescing lamp, and the theory of 
its operation begins. We will, therefore, 
trace in this chapter such theoretical con- 
siderations as enter into the action of the 
incandescing lamp. 

An incandescing lamp may be regarded 
as an electro-receptive device, wherein the 



164 ELECTRIC INCANDESCENT LIGHTING. 

energy of the electric current is being con- 
verted into heat energy, part of which 
is luminous. It is, therefore, necessary, 
at the outset, to determine the amount 
of energy which the lamp is absorb- 
ing. This, as we have already seen, is 
equal to the product of the number of am- 
peres, or the current strength supplied to 
the lamp, and the pressure in volts at the 
lamp terminals. If the resistance of a 
lamp, when hot, is 200 ohms, and the pres- 
sure between the mains 100 volts, then the 
current which will pass through the lamp 

will be - - 1/2 ampere, and the activity 
200 

supplied will be 1/2 X 100 = 50 watts or 
h horse-power. 



The temperature which an activity of 
50 watts, will .produce in a lamp fila- 



THE INCANDESCING LAMP. 165 

merit, depends both upon the extent 
of the surface area of the filament and 
upon the character of its surface. If 
the surface of the filament be large, the 
activity per square inch, or per square cen- 
timetre, will be comparatively small, and 
the filament will not be highly heated. If, 
on the other hand, the surface area of the 
filament be small, the intensity of its sur- 
face activity will be great, and the tem- 
perature of the filament will be high. 
The surface activity of an incandescing 
filament is, approximately, from 70 to 100 

watts per square centimetre, or 450 to 650 

/ 

watts per square inch ; i. e., about T7)^ ns 

o 

to T^ths of a horse-power per square inch 
of surface. 

The electric arc lamp has in its crater, a 



166 ELECTRIC INCANDESCENT LIGHTING. 

surface activity of, approximately, 3 KW, 
or 3,000 watts per square centimetre of sur- 
face; i. e.j 19.35 KW per square inch, or 
27.15 HP per square inch. This shows 
that the surface area of the crater is very 
small, since an arc lamp takes only about 
3/5ths horse-power. The apparent surface 
activity of the sun is, approximately, 
10 KW, or 13.4 HP per square centi- 
metre; i. e,, 64.5 KW, or 86.5 HP per 
square inch. Since, as we have shown, the 
highest frequency of the waves which are 
emitted by a heated surface increases with 
the temperature, it is evident that the 
highest frequency reached in the solar light 
waves will be greater than in the arc light 
waves, and this in its turn will be greater 
than in the incandescent light waves, since 
the intensity of surface activity in watts 
per square centimetre differs so markedly 
in these three surfaces. 



THE 

Collecting these res^ik$^abularly, we 



Solar surface activity, . . . 10,000 watts pei 
Arc-crater surface activity, . . 3,000 watts per square cm. 
Incandescing-filament surface activity, 70 to 100 watts per 
square cm. 

If the surface activity of an incandes- 
cing filament be increased, by passing a 
stronger current through the filament, that 
is, by subjecting it to a higher electric 
pressure, the temperature of the filament 
will increase, and with it the amount of 
light given off per square centimetre. 
This increase may be carried up to the 
point of destruction of the carbon fila- 
ment. The duration or life of an incan- 
descing lamp, depends very markedly 
upon the temperature and surface activity 
of the filament. At a low temperature, 
or at a dull red heat, an incandescing lamp 
will last almost indefinitely ; at a vivid 



168 ELECTRIC INCANDESCENT LIGHTING. 

incandescence, or very high temperature 
and intense surface activity, its life may be 
only a few minutes. Between these two 
extremes lies a mean temperature and sur- 
face activity, at which it has been found 
in practice most profitable and desirable 
to operate the lamp. The object, therefore, 
of the lamp maker is so to proportion the 
dimensions of the filament, that, when con- 
nected across the mains, the surface activity 
will reach the amount necessary to give 
the proper temperature to the filament, as 
well as the desired total quantity of light. 

It should be carefully remembered that 
the surface activity, which determines the 
brightness of the filament, is a quantity 
altogether distinct from the total- candle- 
power, or the total quantity of light given 
off from the lamp. The brilliancy depends 
only on the surface activity, while the 



THE INCANDESCING LAMP. 169 

total candle-power depends upon the total 
surface area as well as upon the brilliancy. 
It is common to find that a person looking 
at two lamps, one of which may have a 
high surface activity; i. e., a great bril- 
liancy, but which only gives say 5-candle- 
power, and the other of which has a low 
surface activity, or small brilliancy, but 
which gives 16-candle-power, will judge 
that the brighter lamp is giving the greater 
amount of light. In other words, the eye 
is very sensitive to relative brightness or 
brilliancy, but is by no means sensitive to 
differences in total-candle-power ; i. e., total 
intensity of the light. It is very essential, 
in all artistic groupings or arrangements 
of lamps, that their surface activity and 
brilliancy should be as nearly equal as 
possible, since, otherwise, appearing to the 
eye unequally bright, they will fail to pro- 
duce pleasing effects. 



170 ELECTRIC INCANDESCENT LIGHTING. 

Having given a certain temperature and 
surface activity to the filament, the total 
amount of light will depend upon the 
total surface area. For example, a 16- 
candle-power lamp, operated at a given 
temperature, or at an efficiency of say 1/3 
candle-per-watt, would take 48 watts of 
activity. A 32-caudle-power lamp, at the 
same brightness, surface activity, and 
quality of carbon filament, and therefore, 
with the same efficiency of 1/3 candle- 
power per watt, would require to be sup- 
plied with 96 watts and would, therefore, 
require double the surface from which to 
radiate the doubled activity. Such a lamp, 
working at the same pressure, would re- 
quire to be both larger in diameter and 
longer. Broadly speaking, a lamp of high 
candle-power will have a thick filament, 
and a lamp of low candle-power a thin 
filament, when working at a common pres- 



THE INCANDESCING LAMP. 171 

sure. Fig. 48, represents the relative sizes 
of incandescent lamps of the same manu- 
facture, voltage and efficiency, intended 
for 16, 32, and 100 candles. Here the 
gradually increasing lengths and diameters 
of the filaments may be observed. 

It may be well to explain in greater 
detail the meaning of the term efficiency, 
as used in the preceding paragraph. 
Since energy must be expended in an in- 
candescing lamp, in order to produce a 
certain candle-power, it is evident, from 
the standpoint of economy in energy, that 
the greater the number of candles which 
can be obtained per horse-power, or per 
watt of activity, the greater will be the 
efficiency of the lamp. We speak, there- 
fore, of the efficiency of an incandescent 
lamp as being l/3rd or l/4th of a candle 
per-watt, meaning that an 8 candle-power 



THE INCANDESCING LAMP. 173 

lamp would take, in either case, 24 or 
32 watts respectively, representing 248.7 
or 186.5 candles per electrical horse-power. 
In common usage, however, the term 
efficiency is often unfortunately misap- 
plied, so that the same lamps would be 
spoken of as having an efficiency of 3 or 4 
watts per candle, respectively, from which 
it would seem that as we increase the num- 
ber of watts to the candle we increase the 
efficiency, whereas, it is evident that the 
reverse is true. It is preferable, therefore, 
to use the word efficiency in the less popu- 
lar but more correct signification. 

When an incandescent lamp is operated 
at a constant pressure, a series of changes 
takes place which it is important to follow 
as closely as the knowledge we possess will 
permit. 

The temperature reached by the fila- 



174 ELECTRIC INCANDESCENT LIGHTING. 

ment of an incandescing lamp has been 
estimated from a series of measurements, to 
be in the neighborhood of 1,350 C., slightly 
varying, however, with the surface activity 
and brightness. 

Thus, at an efficiency of 1/3 candle per 
watt, the temperature is estimated to be 
1,345 C. 

At an efficiency of 1/4 candle per watt, 
the temperature is estimated to be 1,310 
C. 

And at an efficiency of 1/4.5 candle per 
watt, the temperature is estimated to be 
1,290 C. 

If we increase the activity of an incan- 
descing lamp one per cent.; i. e., if we in- 
crease the pressure at its terminals to such 
a point that the number of watts it re- 
ceives increases by one per cent., the tem- 
perature is believed to increase about 2 C. 



THE INCANDESCING LAMP. 175 

and the candle-power is believed to in- 
crease about three per cent. 

When the electric current passing through 
a lamp produces the surface activity and 
temperature for which the lamp is de- 
signed, although, in general, the lamp 
exhibits a steady diminution in tempera- 
ture, surface activity and candle-power, 
which continues while the lamp is used, yet 
it frequently happens, that for the first 
few hours these quantities actually in- 
crease, so that a 16-candle-power lamp, 
after the first fifty hours of its life, may 
give 17 candles, and a greater brightness 
than at the start. Even when this rise 
occurs, however, at the end of the first 
hundred hours the lamp will usually have 
fallen in caudle-power, brilliancy, surface 
activity and temperature, all these quanti- 
ties being associated, to an amount varying 



176 ELECTRIC INCANDESCENT LIGHTING. 

with the type of lamp and the carbon from 
which it has been manufactured. 

We shall now examine the causes which 
bring about the progressive decay of the 
lamp above referred to. When an in- 
candescent lamp is operated, it is found 
that the negative half of the filament 
throws off or projects carbon particles 
from the surface, in all directions in 
straight lines. It is generally believed 
that this effect is due to a species of 
evaporation. This evaporation takes place 
with greatest activity near the negative 
extremity of the filament, or the point 
where the filament is united with the lead- 
ing-in wire on the negative side. From 
this point of maximum evaporation, the 
effect diminishes to the centre of the fila- 
ment and the positive side of the filament 
shows but little evaporation. The presence 



THE INCANDESCING LAMP. 177 

of electric evaporation from negatively 
charged surfaces is recognized at all tem- 
peratures, and even under atmospheric 
pressures, but, like all evaporation, is aided 
by a high temperature and vacuum. Conse- 
quently, its effect is pronounced in an incan- 
descent lamp. ' 

The existence of an evaporation of the 
filament can be detected in a variety of 
ways. For example, if a metallic plate 
be supported in the lamp chamber, mid- 
way between the two legs of an ordinary 
horse-shoe filament, it is found that the 
evaporation of the carbon particles from 
the negative side of the filament, is actually 
capable of carrying an electric current to 
the plate. That is to say, the stream of 
negatively charged carbon particles im- 
pinging against the surface of the metallic 
plate, delivers up to it the electricity with 



178 ELECTRIC INCANDESCENT LIGHTING. 

which they are charged and so results in 
the passage of an electric current. 

The continued evaporation of carbon 
from the surface of the filament, produces 
a gradually increasing blackening of the 
surface of the globe, since the projected 
carbon particles adhere to the walls of the 
chamber where they strike. The con- 
tinued bombardment of the glass walls 
slowly coats them with a layer of carbon, 
which being opaque, reduces the amount 
of light emitted by the lamp. An old 
lamp, if examined against a white surface, 
such as a sheet of paper, will be seen 
to be distinctly blackened over its in- 
terior surface. This blackening, or, as 
it is sometimes called, age coating of the 
lamp chamber, takes place, other things 
being equal, most rapidly in lamps that 
have been burned at a high tempera- 



THE INCANDESCING LAMP. 179 

ture, since in these the evaporation is 
more rapid. 

Another proof that the particles of car- 
bon leave the surface in straight lines is 
to be found in the "shadows" produced 
on the surface of the glass, when the 
filaments are straight horse-shoes, or lie 
wholly in one plane. In such cases the 
bombardment from any portion of the 
negative leg is necessarily intercepted by 
the positive leg in the plane of the fila- 
ment, so that the globe is protected in this 
plane by the interposition of the positive 
leg. The result is, that after the lamp 
chamber is visibly blackened, a distinctly 
marked line can be traced on the sur- 
face of the glass opposite the negative 
leg. The term shadow is sometimes ap- 
plied to this. There will, however, be no 
shadow on the side of the glass nearest to 



180 ELECTRIC INCANDESCENT LIGHTING. 

the negative leg, nor will the shadow be 
produced if the polarity of the supply 
mains is occasionally reversed, or, in the 
case of lamps supplied by alternating cur- 
rents where each leg is positive and neg- 
ative alternately. 

Not only does a lamp filament give less 
light after being operated at high pres- 
sures for a considerable length of time, 
owing to an increase in its resistance and the 
blackening of the globe, butialso to a change 
in the surface nature of the filament, 
whereby it gives less light for a given 
surface activity. In technical language 
its emissivity increases, so that the tem- 
perature, which is attained by a given sur- 
face activity, is reduced. In other words? 
the lower the emissivity of a filament, the 
higher the candle-power and brilliancy for 
a given surface activity. Of these three 



THE INCANDESCING LAMP. 181 

causes for decreased candle-power with age ; 
namely, diminished current strength and 
activity, diminished translucency of the 
globe, and increased emissivity, the loss in 
candle-power is about equally affected by 
each. 

Fig. 49 shows curves representing the 
change in candle-power of an ordinary 
incandescent lamp when initially operated 
at various efficiencies. Thus, at an efficiency 
of 0.3 candle-per-watt, the lamp gives 14.5 
candle-power. At an efficiency of 0.4 
caudle-per-watt, 22.5 candle-power, and 
at 0.5 candle-per-watt, 32 candle-power. 
Roughly speaking, if we double the effi- 
ciency we treble the candle-power and 
brilliancy of the lamp. On this account 
it would obviously be advantageous to 
increase the efficiency of a lamp as far as 
possible. 



182 ELECTRIC INCANDESCENT LIGHTING. 



In the preceding diagram we have 
plotted the relation between candle-power 
and efficiency. If, however, we plot the 
relation between candle-power and activity, 



0.1 0.2 0.3 0.4 

EFFICIENCY. CANDLES PER WATT /" 



0.5 



FIG. 49. CURVE OF HELATTVE CANDLE-POWER OR 
BRIGHTNESS FOR A PARTICULAR CHARACTER OF CAR- 
BON FILAMENT OPERATED AT DIFFERENT EFFICIENCIES. 




183 

we find, rotigid^|^^^^lfiS^ the candle- 
power increases as the cube of the activ- 
ity, so that if we double the activity of 
the lamp ; i. e., increase the pressure at its 
terminals until the product of this in- 
crease of pressure and the increased cur- 
rent is double what it was originally, the 
candle-power of the lamp will be in- 
creased about eight times, giving about 
four times as much light per horse-power 
or per watt expended in the lamp. 

Fig. 50 shows the relation, which has 
been experimentally found to exist, be- 
tween the average lifetime of lamps of the 
same make as that represented in Fig. 49, 
and the efficiency at which such lamps are 
burned. A study of this curve will show 
Why it is not, at present, possible to obtain 
in practice an efficiency beyond a certain 
value ; for, at an efficiency of 0.2 candle- 



184 ELECTRIC INCANDESCENT LIGHTING. 



per-watt, corresponding to 8 candles in the 
particular lamp of Fig. 49, the mean dura- 
tion of life is over 16,000 hours; while at 
0.5 candle-per-watt, corresponding to 32 



1(5,000 
15,000 



13,000 
12,000 



11,000 
10,000 



9,000 
8,000 



7,000 
6,000 
5,000 



o 

X 4,000 



hi 3,000 



2,000 



1,000 



0.1 0.2 0.3 0.4 

EFFICIENCY. CANDLES PER WATT 



FIG. 50. CURVE SHOWING THE MEAN DURATION OP LIFE 
IN A PARTICULAR CLASS OF INCANDESCING LAMPS AT 
VARIOUS EFFICIENCES. 



THE INCANDESCING LAMP. 185 

candles in Fig. 49, the average duration of 
life is only 100 hours. In the first case, we 
should have had an 8-candle-power lamp 
lasting, say 18,000 hours, and representing a 
total output of 144,000 candle-hours, while 
in the second case we have a 32-candle- 
power lamp, lasting only 100 hours, and 
representing a total output of 3^200 candle- 
hours. In the first case, however, the 
candle-power would be obtained from the 
lamp at a comparatively heavy expense in 
energy, 2 1/2 times more energy, in fact, 
than that necessary for a candle in the 
second case. Moreover, the lamp in the 
first case would be very dull in color and 
unpleasant to the eye. 

Between the above two extremes of 
long life and low efficiency, and short life 
and higli efficiency, there exists a certain 
mean value most suitable for commercial 



186 ELECTRIC INCANDESCENT LIGHTING. 

purposes. This mean value, as lamps are 
now constructed, is in the neighborhood of 
0.3 candle-per-watt, representing an aver- 
age life time of 2,000 hours. This dura- 
tion must, however, only be considered as 
the average lifetime, since it frequently 
happens that among a number of lamps 
manufactured by the same process, and 
with equal skill, some may only last about 
100 hours at this efficiency, while others 
may greatly exceed 2,000 hours. 

With any installation of electric lamps, 
it lies, therefore, in the power of the 
engineer in charge of the plant, to so oper- 
ate the lamps that their life may be bril- 
liant but short, or dull but long; as 
will depend entirely upon the pressure 
maintained at the lamp terminals. Thus, 
if a 16-candle-power incandescent lamp, 
intended for an activity of 50 watts, at 115 



THE INCANDESCING LAMP. 187 

volts, and therefore, to be operated at a 

1 (\ 

normal activity of or 0.32 candle-per- 
ou 

watt, be steadily operated at a pressure 
one volt in excess, or 116 volts, its initial 
candle-power will be raised to 17 candles, 
but its lifetime will be abbreviated about 
seventeen per cent. Again, if the pressure 
be steadily maintained at 2 volts excess, or 
117 volts, the initial candle-power will be 
normally 18 candles, but the probable life- 
time will be reduced about thirty-three per 
cent. 



When lamps are placed in somewhat 
inaccessible positions, such as near the ceil- 
ings of high halls, where there is some 
inconvenience in reaching them, it becomes 
particularly objectionable to have to renew 
these lamps too frequently. In order to 
avoid this, the plan is sometimes adopted 



188 ELECTRIC INCANDESCENT LIGHTING. 

of operating the lamps at a comparatively 
low efficiency and brilliancy, thus necessi- 
tating some extra expense in power, but 

greatly prolonging the average lifetime. 

t 

Fig. 51 represents the rate of variation 
of candle-power in similar samples of the 
same type of lamp when operated at dif- 
ferent steady pressures. Curve No. 5 rep- 
resents a 108-volt, 1 6-candle-power lamp 
of 0.286 candle-per-watt normal efficiency, 
operated at 108 volts. The candle-power 
slightly rises to about 16.6 candles, in 90 
hours, and finally falls to 11 candles after 
500 hours. The efficiency of the lamp at 
this time will, of course, be materially 
reduced. 

Curve No. 4 of Fig. 51, represents the 
behavior of a similar lamp operated at 110 
volts pressure. Here the initial candle- 



THE INCANDESCING LAMP. 



189 



power is raised to 17 1/2 candles and after 
500 hours burning, the candle-power is 




200 300 

HOURS 



Fm. 51. CURVES OP CANDLE-POWER IN LAMPS OF SAME 
TYPE OPERATED AT DIFFERENT FIXED EFFICIENCIES. 

about 10 3/4 candles. Curve No. 3 shows 
similar results for a pressure of 112 volts. 



190 ELECTRIC INCANDESCENT LIGHTING. 

Curve No. 2 for 113 volts and Curve No. 
1 for 114 volts. Here the candle-power 





\ 



100 200 300 400 600 600 700 HOO 900 

HOURS 

FIG. 52. CURVES OP CANDLE-POWER OP THE SAME TYPES 
OP LAMP OPERATED AT DIFFERENT EFFICIENCES. 



commences at 24, but is less than 14 after 
200 hours. 



Fig. 52 represents the behavior of four 
similar types of lamps, operated steadily 



THE INCANDESCING LAMP. 191 

at various efficiencies, instead of at various 
pressures. Curve No. 1, represents the 
behavior with 0.25 candle-per-watt ; Curve 
No. 2, 0.286 candle-per-watt; Curve No. 3, 
0.333, and curve No. 4, 0.4 candle-per- 
watt. It will be seen that the high effi- 
ciency lamp falls to fifty per cent, of its 
initial candle-power in 600 hours, while 
the lowest efficiency lamp only loses ten 
per cent, of its candle-power in the same 
time. 

It is evident, therefore, that no matter 
what the initial efficiency of a lamp may 
be, a time will come in its life when its 
efficiency must be low. When this point 
is reached, the amount of activity absorbed 
by the lamp, at constant voltage, is less 
than it was at the outset, seeing that the 
resistance of the attenuated filament is 
increased. On the other hand, the effi- 



192 ELECTRIC INCANDESCENT LIGHTING. 

ciency, or candles-per-watt, has diminished, 
and as regards its light, the electric power 
is more wastefully applied. It becomes, 
therefore, a question whether it would not 
be advisable to discard or break the lam}), 
and replace it by a new one, having a 
greater efficiency. By so doing we incur 
the expense of a new lamp earlier than 
if we waited for the old lamp to break 
naturally, but we utilize the power of the 
central station more economically. 

The question of the smashing point of a 
lamp, or the point in the life of a lamp at 
which it may be deemed more economical 
to replace it by a new one, or its economical 
age, may be considered from three distinct 
standpoints ; namely : 

(1) From the central-station point of 
view. 

(2) From the consumer's point of view. 



THE INCANDESCING LAMP. 193 

(3) From the isolated-plant point of 
view. 

The central station has usually to re- 
place broken or useless lamps, and since 
the charge for service is based upon the 
ampere-hour, or the watt-hour, so long as 
the lamps burn and the consumer is fairly 
satisfied, the smashing point may be indef- 
initely extended. It is to the station man- 
ager's advantage, however, to maintain a 
steady pressure over the system of mains, 
so that the lamps are not forced above 
candle-power and their lives unduly 
abridged. In the best central stations 
great care is, therefore, always taken that 
the pressure is maintained as closely as 
possible to the normal. Should the pres- 
sure become markedly increased, the cost 
of renewing lamps will be rapidly aug- 
mented. Should it become markedly 



194 ELECTRIC INCANDESCENT LIGHTING. 

diminished, the consumers would be dis- 
satisfied. 



From the consumer's point of view the 
lamps would require to be operated at a 
high efficiency regardless of their lifetime, 
since he would thus obtain, from the power 
for which he pays, the highest brilliancy 
and the maximum quantity of light. More- 
over, lamps which will not break before 
becoming seriously dulled, thus necessitat- 
ing their renewal, are a disadvantage. 
From the standpoint of the consumer, there- 
fore, the smashing point of a lamp is reached 
as early as possible, or at the opposite ex- 
treme to that of the station manager. 

From the standpoint of the owner of the 
isolated plant, who is both producer and 
consumer, the smashing point will neces- 
sarily occupy some intermediate position; 




195 

Desires to 
light for the 
activity produced or coal consumed, on the 
other hand he wishes to reduce the cost of 
lamp renewals as far as possible. No pre- 
cise rule, however, can be laid down. 

There are in general, two purposes for 
which light is ordinarily employed ; namely, 
for actual use, as in reading, or other work, 
and for the aesthetic purposes of ornamen- 
tation. Regarding the latter purpose as 
a luxury, lamps may be changed as often 
as taste may dictate, but high-efficiency, 
high-brilliancy, short-lived lamps will be 
preferable. On the other hand, so long as 
a lamp fulfills the utilitarian purpose of 
enabling work to be conveniently and 
healthfully performed, it is waste of money 
to throw the lamp away. The smashing 
point, therefore of lamps intended to 



196 ELECTRIC INCANDESCENT LIGHTING. 

illumine working rooms depends largely 
upon the total candle-power installed. If 
this is ample in the first instance, a very 
considerable falling off in candle-power 
may be permitted without interfering with 
the usefulness of the light, and economy is 
rarely pushed to such a degree as to limit 
closely the candle-power installed for pur- 
poses of reading or working. 

It is found, however, that in central 
station practice the best commercial results 
are secured with ample satisfaction to the 
consumers, if the efficiency at which the 
lamps are operated on the system, is such 
that the cost of lamp renewals is approx- 
imately fifteen per cent, of the total opera- 
ting expenses of the station. Where the 
pressures between the mains can be closely 
regulated, it is preferable to employ high- 
efficiency lamps, but where the reverse is 



THE INCANDESCING LAMP. 197 

the case, low-efficiency lamps are desirable, 
since a low-efficiency lamp can stand an 
accidental increase in pressure with less 
detriment to its length of life than a high- 
efficiency lamp ; for, being normally oper- 
ated at a lower temperature, an increase of 
temperature may not be dangerous. 



CHAPTER X. 

LIGHT AND ILLUMINATION. 

THERE are two technical words which 
are very apt to be confused in their 
meaning, and misused in their applica- 
tion; namely, " light " and "illumination." 
When correctly used, the word light signi- 
fies the flow or flux of light emitted by a 
luminous source, irrespective of the sur- 
face on which it falls, while the word 
illumination means the quantity of light 
received on a surface, per unit of area, 
whether received directly from the lumin- 
ous source, or indirectly by diffusion and 
reflection from surrounding bodies. The 
words " light " and " illumination " are unf or- 



198 



LIGHT AND ILLUMINATION. 199 

tunately often used synonymously, whereas 
it is evident that they denote distinct 
ideas. 

By the candle-power of a source of light, 
we mean the luminous intensity of the 
source as measured in units of luminous 
intensity. The unit of luminous intensity, 
commonly employed, is the British candle, 
and is equal to the intensity of light pro- 
duced by a candle of definite dimensions 
and composition, burning at the rate of 2 
grains, or 0.1296 gramme, per minute. If 
we speak of a source of light as having, 
say a luminous intensity of 20 British 
standard candles, we mean that if that 
source were reduced to a mere point, it 
would yield as much light as 20 standard 
candles all concentrated at a single point. 

A standard of luminous intensity very 



200 ELECTRIC INCANDESCENT LIGHTING. 

generally adopted, except, perhaps, in 
English-speaking countries, is the Frencli 
standard candle, called the bougie-decimale, 
or the 1/2 Oth of the intensity of an 
international standard unit called the 
Viotte. The Violle is a unit of lumin- 
ous intensity produced in a perpendicular 
direction, by a square centimetre of plati- 
num, at the temperature of its solidifi- 
cation. The British standard candle is 
slightly in excess of the bougie-decimale, 
one British candle according to Everett 
being 1.012 bougie-decimale. 

If we imagine a point source of light, of 
unit intensity ; i. e., one standard French 
candle, or bougie-decimale, to be placed at 
the centre of a hollow sphere, of the radius 
of one metre, or 39.37", then the total 
internal surface of the sphere will receive 
a definite total quantity of light. Each 



gJiBBttfljggs. 

c^ X f fy' 

4 PROPERTY OF 1 JI9 

yMGHT AND ILLUMINATION. ^'// 201 

V4b 

unit of 

spherical nrimTTpwffl-TT^^ unit of 

light ; and, since the total interior surface 
of such a sphere contains 4 X 3.1416 = 
12.566 square metres, the total quantity of 
light received on the interior surface will 
be 12.566 units, called lumens. Conse- 
quently, if a point source of unit intensity 
emits 12.566 lumens, a source, of say 20 
bougie-decimales, would yield an intensity 
of 251.32 lumens. 

It is obviously not necessary that the 
surface, which surrounds the unit point 
source, should be spherical. The same 
amount of light; namely, 12.566 lumens, 
will be given off by the source independ- 
ently of the shape of the receiving surface, 
so that when such a source is placed, for 
example, alone in a room, the total 
quantity of light which falls directly upon 



202 ELECTRIC INCANDESCENT LIGHTING. 

the walls, ceiling and floor of the room- 
from the source, will be 12.566 lumens. 
This will be true in fact if there are other 
sources of light in the room at the same 
time. The quantity of light which each 
point source will emit will be 12.566 
times its luminous intensity. 

If one lumen falls perpendicularly and 
uniformly over the surface of one metre, 
the illumination of that surface will be 
one lux, the lux being the unit of illumi- 
nation. If, for example, a bougie-decimale 
is located at the centre of a sphere of one 
metre radius, then each square metre of 
the interior surface of the sphere will 
receive one lumen of light, and this light 
falls everywhere perpendicularly upon its 
surface. The illumination on the interior 
surface is everywhere one lux. A bougie- 
decimale produces, therefore, when acting 



LIGHT AND ILLUMINATION. 203 

alone, an illumination of one lux at a dis- 
tance of one metre. 

The mistake is not infrequently made, 
that because a surface receives light 
directly from a given source of known 
intensity, its illumination can be deter- 
mined by mere calculation of its distance 
from the source. It must be remembered 
that it also receives reflected or diffused 
light from all neighboring surfaces, which, 
consequently, tend to increase its illumina- 
tion. 

The law of illumination from a single 
point source, acting alone ; i. e., in a space 
where all reflected or other light is ex- 
cluded, is that the illumination varies 
inversely as the square of the distance 
from the source. Thus, we know that a 
bougie-decimale produces an illumination 



204 ELECTRIC INCANDESCENT LIGHTING. 

of one lux upon a surface held perpen- 
dicularly to the rays of light at a distance 
of one metre. If the surface be held at 
a distance of 2 metres from the point 
source, in a room otherwise dark, the 
illumination will be l/4th of a lux, or 
(l/2) a ; at a distance of 3 metres the 
illumination would be similarly l/9th lux, 
or (1/3) 2 . Generally, a point source, of say 
50 bougie-decimales, would produce, at a 
distance of say 5 metres, an illumination of 

50 

-^ = 2 luxes. 

In practice, if a surface were placed in 
a room at a distance of 5 metres from 
a source of 50 bougie-decimales, the illu- 
mination received, if the rays be allowed 
to fall perpendicularly upon the surface, 
will be more than 2 luxes, because this 
amount of illumination will be produced 



LIGHT AND ILLUMINATION. 205 

by the direct action of the source in a 
space from which all other light was ex- 
cluded, whereas, reflection from the walls 
of the rooms, mirrors, ceilings, etc., will 
increase this amount of illumination to, 
perhaps, 10 luxes, and, if it were possible 
to have the surfaces of the walls perfectly 
reflecting, the illumination which would 
be produced in all parts of the room 
would be indefinitely great. Conse- 
quently, the amount of illumination 
received upon the surface of a desk or 
table, depends not only upon the number 
of lamps in a room, on their candle-power 
and arrangement, but also upon the char- 
acter of the surfaces of the walls and 
furniture. Therefore, the question of 
lighting a room is not altogether a ques- 
tion of its dimensions and of the total 
candle-power placed in it, but also depends 
upon the arrangement of the lamps, and 



206 ELECTRIC INCANDESCENT LIGHTING. 

the character of the decoration and furni- 
ture, and the nature of their reflecting 
surfaces. 

The illumination required for comfort- 
able reading is from 15 to 25 luxes on 
the surface of a printed page. Any 
illumination less than 10 luxes is fati- 
guing, if long continued. The illumina- 
tion produced by full moonlight is about 
l/8th lux, and that by full sunlight 
80,000 luxes. The illumination in a 
street as ordinarily lighted by arc lamps, 
is, perhaps, 50 luxes near the ground 
below an arc lamp, and about 1 lux 
near the ground midway between the 
lamps. 

The luminous intensit}^ of an incan- 
descent lamp is not the same in all direc- 
tions, owing to the fact that the filament 




is not a 
positions, 

is exposed th n TTtff-nttiTrry J ffiffTn simph 
horse-shoe filament, with both legs in 
one plane, gives less light in this plane 
than in any other plane passing through 
the vertical, because each leg intercepts 
the light from the other. The mean 
spherical candle-power of a lamp, in bou- 
gie-decimales, is the quantity of light it 
emits in lumens, divided by 12.566. In 
other words, the mean spherical candle- 
power of a lamp is the equivalent point 
source which emits as much light in all 
directions as the actual lamp does. 
The spherical candle-power of an incan- 
descent lamp is usually about twenty per 
cent, less than its maximum horizondl in- 
tensity, so that when we speak of a 16- 
candle-power lamp, a point source of about 
13 candles intensity would supply the same 



208 ELECTRIC INCANDESCENT LIGHTING. 

total number of lumens as is emitted from 
the actual lamp. A point source would 
Lave no base or socket and would disperse 
light equally in all directions. 

It may be of interest to note that a 
lux-second, that is to say, the total time- 
illumination produced by one lux for one 
second of time, has been accepted by the 
International Photographic Congress of 
Brussels as the unit of time-illumination, 
under the name of the pilot. A phot is 
a lux-second, and is a unit of time illumina- 
tion employed in photography. It is well 
known in photography that the actinic 
effect of light, that is its power of effect- 
ing chemical decomposition as utilized in 
photography, depends, for a given quality 
of light, both on its intensity and on the 
duration of its action. In photography, 
therefore, this practical unit was required 



LIGHT AND ILLUMINATION. 209 

to represent tlie product of illumination 
and time. 

The caudle-power of incandescent lamps 
varies from 1/2 candle up to 100 British 
Standard candles, although both larger 
and smaller candle-powers have been 
specially prepared. The 16-candle-power 
lamp is generally employed in the United 
States, and the 10-candle-power lamp is 
generally employed in Europe. The sizes 
usually manufactured are 1/2, 1, 2, 3, 4, 5, 
6, 8, 10, 16, 20, 32, 50, 60 and 100. 



CHAPTER XI. 

SYSTEMS OF LAMP DISTRIBUTION. 

BROADLY speaking, there are two gen- 
eral methods by means of which lamps 
may be connected with a generating source 
of electricity ; namely, in series, so that 
the current passes successively through 
each lamp before it returns to the source, 
and in multiple or parallel; so that 
the current divides and a portion passes 
through each lamp. 

Fig. 53, represents three lamps con- 
nected in series, and Fig. 54, represents 
three lamps connected in parallel. In the 
case of the series connection shown in Fig. 



210 



SYSTEMS OF LAMP DISTRIBUTION. 211 

53, the three lamps are so connected that 
the current from the source, entering the 
line at +, flows in the direction indicated 
by the arrows, passes successively through 
the lamps A, B, and C\ returning to the 






FIG. 53. SERIES-CONNECTED LAMPS. 

source at the negative end of the line. In 
Fig. 54, the three lamps A, B, C f , are con- 
nected as shown, to the positive and nega- 
tive leads respectively, and the current 
passes through them in the direction indi- 
cated by the arrows. The arterial system 
of the human body furnishes an example 



212 ELECTRIC INCANDESCENT LIGHTING. 



of a parallel or multiple system, since the 
blood flow divides into a very great num- 
ber of different channels or capillaries, 
and, after passing through these independ- 






FIG. 54. MULTIPLE-CONNECTED LAMPS. 

ent channels, finally unites in the veins 
and returns to the heart. 

In order to compare the relative advan- 
tages of the series and multiple methods 
of electric distribution, let us suppose that 
a house has to be lighted electrically at a 
distance of a mile from the dynamo, and 
that for this purpose an amount of light 
represented by 1,000 candles is required, 



SYSTEMS OF LAMP DISTRIBUTION. 213 

distributed in 50, 20-candle-power lamps. 
Further, let us assume that the same 
efficiency is secured in the operation of 
these lamps, whatever system we may 
adopt, or whatever dimensions the lamp 
filament may take, a supposition in accord- 
ance with general practice. Let us sup- 
pose that this efficiency will be 1/4 candle 
per watt. We shall then require to ex- 
pend 4,000 watts of electric energy in the 
lamp filaments in the house. This amount 
of activity might be electrically expended 
in a great variety of ways, as regards the 
pressure and current of delivery, but it 
will suffice to compare two ways only; 
namely, the delivery of 4 amperes at a 
pressure of 1,000 volts, and the delivery 
of 1,000 amperes, at a pressure of 4 volts. 
In each of these two cases the activity 
delivered will be the same; namely 4 
KW. 



214 ELECTRIC INCANDESCENT LIGHTING. 

If it be required to expend only 1,000 
watts in the main conductors carrying the 
current to the house, when all the lamps 
are turned on, 5,000 watts or 5 KW will 
have to be supplied at the generator termi- 
nals, of which twenty per cent., or 1,000 
watts, is permitted to be lost in transmis- 
sion in the leads, as heat. We know that 
this loss will be the product of the current 
strength and the drop in volts in the two 
conductors. In the first plan of 1,000 
volts and 4 amperes at the house, the drop 
of pressure in the two wires must be 250 
volts, in order that 250 volts X 4 am- 
peres = 1,000 watts, so that the resistance 
of the two wires together, which shall 
produce a drop of 250 volts, with a cur- 
rent of 4 amperes, will be 62 1/2 ohms, or 
31 1/4 ohms to each wire one mile in 
length. The nearest size of wire to that 
which has a resistance of 31 1/4 ohms to 



SYSTEMS OF LAMP DISTRIBUTION. 215 

the mile, is, No. 18 B. & S. or A. W. G., 
having a diameter of 0.0403", or, approxi- 

mately, the ^th of ail inch. Such a wire 
2f) 

would weigh about 26 Ibs. and the two 
wires forming the complete circuit would 
weigh about 52 Ibs. 

Considering the second plan of 4 volts 
and 1,000 amperes, the drop in the wires 
would have to be only one volt. In order 
that the activity expended in them should 
be 1 KW since 1 volt x 1,000 amperes = 
1 KW the resistance in the two wires 
together, to permit of a drop of but 1 

volt with 1,000 amperes, must be / 
of an ohm, since 1,000 amperes x 



ohm = 1 volt. The two wires together 
must, therefore, have a resistance of 



216 ELECTRIC INCANDESCENT LIGHTING. 

ohm, or each must have a resistance of 
th ohm. A wire which would have 

this resistance would have 62,500 times 
the cross-section and weight of the wire in 
the preceding case ; so that, instead of re- 
quiring 52 Ibs. of copper, in all, for the 
two miles of conductor, we should require 
approximately 3,250,000 Ibs., or 1,625 
short tons of copper. 

It is, therefore, evident that although a 
given electric activity can be expended in 
incandescent filaments either at a high 
pressure or at a low pressure, the advan- 
tage of a high pressure is very great, when 
the power is to be transmitted electrically 
to a distance. If we double the pressure 
of transmission ; i. e., if we double the 
number of volts between the two main 
conductors, we require four times less cop- 



SYSTEMS OF LAMP DISTKIBUTION. 217 

per for a given percentage of loss of 
activity in them. Thus, in the preceding 
case, when we increased the pressure of 
delivery from 4 volts to 1,000 volts, we 
increased it 250 times, and, therefore, w r e 
diminished the amount of copper which 
was required for twenty per cent, loss, 250 
X 250 or 62,500 times. Consequently, the 
first essential for economical distribution 
of electric power to a distance, either for 
lamps, or for any other purposes, is high 
electric pressure of delivery. 

If then we adopt provisionally, the plan 
of supplying the house above considered 
at a pressure of 1,000 volts and 4 am- 
peres, this would appear to be most readily 
carried out at first sight, by connecting 
50 lamps in a single series through the 
house, each lamp being intended for 20 
volts and 4 amperes. When all the lamps 



218 ELECTRIC INCANDESCENT LIGHTING. 

are lighted, the total current would be 4 
amperes, when the total pressure of de- 
livery amounted to 50 x 20, or 1,000 volts. 
Though such a system could, doubtless, be 
installed, yet it would possess several dis- 
advantages. In the first place, unless some 
device were provided whereby a faulty 
lamp became automatically short-circuited, 
the failure of any single lamp would 
interrupt the entire circuit and extinguish 
all the other lamps. Moreover, the pres- 
sure which would have to be supplied to 
the house between the main conductors 
would depend upon the number of lamps 
employed. When a single lamp only was 
lighted, the pressure required would be 20 
volts and the current 4 amperes. This 
would mean that the generating dynamo 
in the station supplying the house could 
only be used for that particular house, 
since, if two houses were supplied from 



SYSTEMS OF LAMP DISTRIBUTION. 219 

the same dynamo, one might have all the 
lamps turned on and thus require 1,000 
volts and 4 amperes, while the other 
might have only half its lamps turned on, 
thus requiring 500 volts and 4 amperes. 
For this and other reasons it is now uni- 
versally considered that incandescent light- 
ing on any extended scale must necessarily 
be conducted by a multiple-arc system. 

It would be practically impossible to 
construct incandescent lamps capable of 
being operated in parallel at the pressure 
of 1,000 volts assumed in this case; for, 

each lamp would have to be capable of 

4 
taking a current of ths ampere, at a 

pressure of 1,000 volts. The resistance 
would have to be 12,500 ohms hot, so that 
the filament would have to be very fine 
and long. Such a lamp would be quite 



220 ELECTRIC INCANDESCENT LIGHTING. 

impracticable, and, moreover, the pressure 
of 1,000 volts is not considered safe to 
introduce into a building. The maximum 
pressure for which it has been possible, 
until recently, to construct incandescent 
lamps has been 120 volts, so that incandes- 
cent lighting between a single pair of 
conductors has been practically limited to 
a pressure of 115 volts at the lamp 
terminals. 

The lack of economy of 11 5- volt pres- 
sures for incandescent lighting at a dis- 
tance, as regards the amount of copper 
required, was early apparent, and a method 
was invented and introduced which is 
practically a compromise between the 
series and parallel systems ; that is to say 
a method was invented whereby the ad- 
vantages of the parallel connection of 
lamps were secured, together with the 



SYSTEMS OF LAMP DISTRIBUTION. 221 

advantage of higher pressure obtained by 
coupling lamps in series. This method is 
fundamentally what is called a series-mul- 
tiple system, and in practice is what is 
generally called the three-wire system. 

A + 




c c 

FIG. 55. THREE- WIRE SYSTEM, SERIES-MULTIPLE CON- 
NECTION. 

The three-wire system is illustrated in 
Fig. 55. Here there are two multiple-arc 
circuits, one between the mains A and B, 
and the other between the mains B and C. 
Between each of these pairs of mains the 
pressure is 115 volts, supplied by a sepa- 
rate dynamo as shown. The positive 
terminal of the dynamo D 2 , being con- 



222 ELECTRIC INCANDESCENT LIGHTING. 

nected to the negative terminal of $ the 
dynamo D ly it is evident that between the 
mains A A and C C, there will be a pres- 
sure of 230 volts. In the case shown 
there are 12 lamps in all, or 6 on each 
side of the system, so that about 3 
amperes will be flowing through the mains 
A A and C O, and no current will pass 
through the neutral conductor B B. If 
the number of lamps on the two sides of 
the system be unequal, the difference be- 
tween the current strengths will return 
by the neutral conductor ; for example, 
if all the lamps between B and C, are 
turned off, 3 amperes will flow along the 
positive main A A, and return by the 
neutral main B B, no current passing 
through the negative main. Since, on the 
average, when the Aviring is judiciously 
carried out, the loads on the two sides of 
the system will usually nearly balance each 




223 

other, ^^^ei^tjral conelucton^ifjxjpfily have 
to carry ast^afli^ua^oi^f^Te current in 
the outside mains, and may therefore be 
much lighter. If the neutral conductor 
could be entirely dispensed with, we 
know that the copper required to sup- 
ply the system with a given percentage of 
loss in transmission would be four times 
less on the three-wire system, than on 
the two-wire system, since the pressure 
of distribution would be doubled. The 
three-wire system would, therefore, ensure 
a saving of seventy -five per cent, in the 
amount of copper required for the mains. 
In practice, however, the amount of copper 
in the neutral conductor averages, over 
an entire system, about sixty per cent, 
of that in the outside conductor, so the 
neutral is made a little more than half 
as heavy as either of the outside mains. 
Under these conditions, the actual saving 



224 ELECTRIC INCANDESCENT LIGHTING. 

in weight of copper throughout the supply 
conductors of a three- wire system is about 
67 1/2 per cent, over that necessary for a 
two-wire system having the same loss in 
transmission. 



A-f 



) <> 




c 
FIG. 56. MULTIPLE-SERIES CONNECTION. 

Fig. 56 represents a multiple-series sys- 
tem equivalent to a three-wire system with 
no neutral, and supplied at 230 volts pres- 
sure. The disadvantage of such a system, 
however, is that two lamps have to be 
turned on and off simultaneously. The 
three- wire system of Fig. 55 gives inde- 
pendent control over every lamp. 



SYSTEMS OF LAMP DISTRIBUTION. 225 

The principle of the three-wire system 
has been extended to four- and five-wire 
systems. Four-wire systems are very rare. 
Five-wire systems are employed in Europe 
but have never come into favor in the 
United States. A five-wire system saves 
about ninety per cent, of the copper re- 
quired for a two-wire system, but requires 
four dynamos in series at the central sta- 
tion, five sets of conductors and complica- 
tion in house wiring and meters. 

The three-wire system is in very 
extended use in the United States. It 
commonly happens that one three-wire 
central station will distribute light and 
power over an area whose radius is some- 
what greater than one mile, whereas, with- 
out the use of the three- wire system, the 
radius of commercial incandescent lighting 
from a central station would be probably 



226 ELECTRIC INCANDESCENT LIGHTING. 

only about one-half a mile or eight times 
less area. 

The drop of pressure, which is permitted 
in incandescent lighting, does not depend 
entirely upon the activity uselessly ex- 
pended in the main conductors. For ex- 
ample, in cases where capital would be 
difficult to secure, and the interest upon 
the capital invested would be large, it 
would be desirable to employ compara- 
tively small conductors, and waste a com- 
paratively large percentage of the total 
power in them. This would necessitate a 
comparatively great difference of electric 
pressure between the lamp terminals and 
the generator terminals. In the case of a 
single house supplied with 115-volt lamps, 
it would not be a matter of much conse- 
quence whether the pressure at the central 
station were 116 or 166 volts, provided 



SYSTEMS OF LAMP DISTRIBUTION. 227 

the lamp pressure remained constant, but 
where incandescent lamps are distributed 
along street mains, in a city, and have 
to be supplied at all distances from a few 
yards to a mile or more from the central 
station, it is absolutely necessary that the 
pressure shall be nearly uniform through- 
out the system, since, otherwise, the lamps 
in or near the station will be at an 
unduly high pressure, and will conse- 
quently *be brilliant and short-lived, while 
the more distant lamps will be burned at 
an unduly low pressure, and be dull and 
long-lived. The drop of pressure permis- 
sible in the supply conductors is, conse- 
quently, as much a matter of regulation 
of pressure, and of uniformity of candle- 
power, as it is a consideration of economy 
in the transmission of electric power. If 
lamps were less sensitive to changes in 
pressure than they are, the amount of cop- 



228 ELECTRIC INCANDESCENT LIGHTING. 

per which would be employed in incan- 
descent lighting would be less than it 
actually is, but all the improvements made 
of recent years in incandescent lamps have 
been improvements in their efficiency, 
whereby a smaller amount of activity is 
required for a given production of light, 
and this, as we have seen, is attended by 
the development of a higher tempera- 
ture and a greater sensibility to variations 
in pressure, so that the most economical 
lamps are also lamps which, other things 
being equal, require a closer regulation of 
pressure at their terminals. 

The difficulty of maintaining a nearly uni- 
form pressure over all parts of the mains of 
a large incandescent system has been largely 
overcome by the use of what are called 
feeders. A feeder differs from an ordinaiy 
supply conductor, or main, in that no lamp 



SYSTEMS OF LAMP DISTRIBUTION. 229 

or receptive device is directly connected 
with it ; its sole purpose being to supply 
the mains from the central station at some 
distant point as indicated in Fig. 57. 
Here D, is the dynamo at the central 
station. F F, are feeders carrying the 
current from the dynamo to some cen- 



J ) 
i i 



F 

FIG. 57. FEEDER DISTRIBUTION. 



tral point in the mains A A ly B B^ 
In this way the difference in pressure be- 
tween the various lamps depends only 
on the drop of pressure in the mains, and 
not on the drop of pressure in the feeder. 
Thus, if the pressure at the lamps at A and 
A l9 be 115 volts, the pressure at the feed- 
ing point F, may be 116 volts, while the 
pressure at the dynamo may be 150 volts. 



230 ELECTRIC INCANDESCENT LIGHTING. 

If the same lamps were supplied without 
feeders as shown in Fig. 58, and the same 
limiting difference of pressure maintained 
between the lamps as in Fig. 57, namely 1 
volt, it would be necessary to have prac- 
tically 116 volts at the dynamo terminals 
and 115 volts at the most distant lamp. 



B 

FIG. 58. TREE DISTRIBUTION. 

This probably would require much more 
copper in supply conductors than when 
feeders are employed. The conductors in 
Fig. 58 are shown as tapering or diminish- 
ing in size towards the distant end. 

Feeders may equally well be applied to 
three-wire systems. Fig. 59 represents 
diagrammatically the supply-mains of a 
city district containing four blocks, 1, 2, 3 



SYSTEMS OF LAMP DISTRIBUTION. 



231 



and 4. Here the three- wire mains extend 
round the block-facings in one continuous 
network. These mains are supplied from 
the central station at S 9 by the three- wire 



FIG. 59. DIAGRAM OP THREE- WIRE FEEDER 
DISTRIBUTION. 

feeders represented by the dotted lines, at 
the feeding points, A, B, C and D. In 
this way the pressure in the network of 
mains may be within two per cent, of the 
mean value, of say, 115 volts, while the 
pressure at the central station may be 130 
volts, representing a drop in the feeders of 



232 ELECTRIC INCANDESCENT LIGHTING. 

15 volts. If the lamps were connected 
across the feeders they would be subjected 
to a total difference of pressure, over the 
entire system, amounting to 17 volts, but, 
by connecting the lamps to the mains only, 
they are rendered entirely independent of 
the drop which occurs in the feeders. 

If the system of mains be unequally 
loaded, as for example, when the area over 
which they extend, comprises both a resi- 
dence district and a business district, so 
that the load shifts in the morning and 
afternoon to the business district, and in 
the evening, almost entirely to the resi- 
dence district, it may happen that the 
load on some particular feeders may be 
much greater than the load on others. 
Consequently, the drop in the loaded 
feeders will be in excess of that on the 
comparatively idle feeders. Under these 



SYSTEMS OF LAMP DISTRIBUTION. 233 

circumstances, the pressure at the mains, 
near the terminals of the idle feeders, will 
be higher than that at the terminals of the 
loaded feeders, thus bringing about an 
inequality of pressure, prejudicial to the 
life and proper performance of the lamps. 

The difficulty arising from the inequal- 
ity in the feeder load may be overcome in 
one or more of four ways : 

(1) By disconnecting certain feeders 
from the bus-bars, or main terminals in a 
central station, so as to increase the load 
and drop on the remaining feeders. 

(2) By introducing artificial resistances, 
called feeder regulators, into the circuit of 
the idle feeders; so as to increase artificially 
the drop of pressure which exists in them. 

(3) By employing more than one pres- 
sure in the central station, that is to say, 
by having one set of dynamos operating at 



234 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 60. FEEDER EQUALIZER RESISTANCE. 




LAMP DISTRIBUT^W 235 

for the 



a pressure 

supply of the shorter feeders to tlie area 
AN 7 ithin the vicinity, and another set of 
dynamos delivering, perhaps, 135 volts, for 




FIG. 61. EQUALIZER SWITCH. 

the supply of longer feeders connected to 
the outlying districts. 

(4) By introducing more copper into 
the system, either in the form of additional 



236 ELECTRIC INCANDESCENT LIGHTING. 

feeders, so as to share and equalize the 
load, or in the form of more numerous 
mains to distribute and equalize the pres- 
sure. 

Fig. 60, represents a form of resistance, 
suitable for feeder regulation. Here a 
number of spirals of heavy iron wire are 
mounted in a fire-proof frame and so 
arranged that under the influence of the 
handle and switch, shown in Fig. 61, they 
may be inserted in the circuit of a feeder 
either in parallel or miseries. 

In modern large central stations feeder 
equalizers are rarely employed. The best 
practice employs more than one pressure. 



CHAPTER XII. 

HOUSE FIXTURES AND WIRING. 

THE incandescent lamp, when located in 
a house, is either installed as a fixture, or a 
certain freedom of motion is given to it, 
so that, within certain limits, the lamp is 
portable. This portability is effected by 
maintaining the lamp in connection with 
the mains by means of a flexible conductor 
or lamp cord, usually called a flexible cord. 
The lamp is then portable to the extent 
of the length of the cord. Various forms 
are given to portable lamps, two of which 
are shown in Figs. 62 and 63. In Fig. 62, 
the flexible cord c c, is attached to a read- 
ing lamp, mounted on a stand as shown. 



238 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 62. PORTABLE LAMP FOII DESK USE. 

This lamp can be raised and lowered 
within a limited range, as well as turned 



HOUSE FIXTURES AND WIRING. 239 




FIG. 63. FLEXIBLE LAMP PENDANT WITH ADJUSTER. 



240 ELECTRIC INCANDESCENT LIGHTING. 

about its axis without shifting the base. 
Fig. 63, shows a form of movable lamp, in 
which a limited portability is obtained by 
what is generally known as a flexible 
pendant. Here the lamp is hung from 




FIG. 64. FLEXIBLE SUPPORT FOB LAMP. 

the ceiling by a flexible lamp cord. By 
means of an adjuster J^ the lamp can be 
raised or lowered. 

The limited portability given to a lamp, 
by attaching it to a sufficiently long 



HOUSE FIXTURES AND WIRING. 241 

flexible pendant, enables the light to be 
applied to a variety of purposes, such, for 
example, as the lighting of a music stand, 




FIG. 65. FLEXIBLE SUPPORT FOR DESK LAMP. 

as shown in Fig. 64, or the lighting of a 
desk, as shown in Fig. 65. Fig. 66, shows 
a device for tilting a flexible pendent lamp 
in any desired direction. 

Fixed lamps, as their name indicates, 
are lamps attached to electric fixtures, and, 



242 ELECTRIC INCANDESCENT LIGHTING. 

therefore, cannot be moved. They take a 
great variety of forms, such as the bracket 
lamp shown in Fig. 67, designed for 




Jflfe 



FIG. 66. TILTED LAMP. 



For ceiling 



attachment to the wall, 
attachment, lamps are either made of the 
simple pendant type, as shown in Fig. 68, 
or several lamps are placed 



together 



HOUSE FIXTURES AND WIRING. 243 

in a cluster in an electrolier, as shown in 
Fig. 69. As in gas lighting, the incandes- 
cent bracket lamp is sometimes given a 
movable arm so as to permit the lamp to 




FIG. 67. BRACKET LAMP. 

be moved in one plane, within a certain 
radius. Such a lamp is shown in Fig 70. 

The size of the wire employed inside 
a house will depend upon the amount of 
current which the conductor is designed to 



244 ELECTRIC INCANDESCENT LIGHTING. 



FIG. 68. PENDANT LAMP. 



HOUSE FIXTURES AND WIRING. 



245 



carry. When of small size, the conductor 
is given the form of a single wire, but, 




FIG. 69. ELECTROLIER. 



in order to secure greater flexibility, larger 
sizes are almost invariably stranded, that 



246 ELECTRIC INCANDESCENT LIGHTING. 

is, composed of several independent wires. 
The former are called solid wires and the 
latter stranded wires. In Fig. 71, the 
solid conductor is marked <?, and has one 
coating of insulator d, which is afterward 





FIG. 70. BRACKET LAMP WITH MOVABLE ARM. 

covered by a braiding b. The stranded 
conductor shown at C\ consists of seven 
wires, twisted together as shown, and is 
covered by two coatings of insulating 
material, I) and E, respectively, and 
finally by a coating of braid B. 

Fig. 72, shows two other forms of 
stranded conductors ; the wire marked A, 



HOUSE FIXTURES AND WIRING. 



247 



is provided with a highly insulating 
material called okonite ; that marked B, 
has in addition, a coating of braid. The 
wire at A, is equivalent to No. 6 A.W. Gr. 




d b 

FIG. 71. SOLID AND STRANDED CONDUCTORS. 

in cross-sectional area. The insulation re- 
sistance of a mile of this wire, when sub- 
merged in water, is 1,000 million ohms, 
that is, one billion ohms, or a begohm. 

A flexible cord, such as has already 
been referred to in connection with port- 
able lamps, is necessarily a double con- 



248 ELECTRIC INCANDESCENT LIGHTING. 

due tor, since the current must be passed 
both into and out of the lamp. These 
two conductors are separately insulated, 
and are then either twisted together, form- 
ing what is called a twisted double con- 





FIG. 72. OKONITE-COVERED STRANDED WIRES. 

ductor, or are laid side by side, and laced 
together by a covering of braid, forming 
what are then called parallel or twin con- 
ductors. Fig. 73, shows some forms of 
double flexible conductors. These are 
first separately insulated and are then silk- 
covered. They are sometimes technically 
called silk lamp cord. In order to attain 



HOUSE FIXTURES AND WIRING. 249 

the flexibility required in such cords they 
are composed of a comparatively large 
number of fine copper wires stranded to- 
gether. 





FIG. 73. FORMS OF DOUBLE FLEXIBLE CONDUCTORS. 

We will now trace the network of con- 
ductors in a house which we will suppose 
receives its current from the street 
mains, to the lamps in the different por- 
tions of the house. First; proceeding 
from the street to the house, we find a set 
of conductors leading into the house, 



250 ELECTRIC INCANDESCENT LIGHTING. 

called the service wires. These in a two- 
wire system consist of two conductors, and 
in a three-wire system of three conductors. 
Within the house the system of conduct- 
ors may be arranged under the following 
heads; namely, 

(1) The risers, or the supply wires 
which carry the current up from the ser- 
vice wires to the different floors of the 
house. They may be a single set or a 
multiple set, but each set will be double 
or triple according as the house is wired 
on the two- or three-wire system. 

(2) The mairts, or the principal supply 
conductors running from the risers or ser- 
vice wires along the different corridors or 
passages. There are usually as many sep- 
arate systems of mains as there are floors. 

(3) The sub-mains or the supply-con- 
ductors which branch off from the mains 
along the side passages. 




(4) jBT$&$t fft.jfffl^ qpj|$fed^m>m the 
mains into i^T^uuIiIi?"uT **to fixtures in 
halls. Roughly speaking, therefore, the 
risers correspond to the trunk of a tree 
through which the sap is fed ; the mains 
correspond to the boughs ; the sub-mains 
to the smaller boughs ; and the branches 
to the twigs. The lamps or fixtures cor- 
respond to the leaves and flowers. 

Risers are usually of larger cross-section 
than the mains; the mains are of larger 
cross-section than the sub-mains, and the 
sub-mains, in their turn, are larger than 
the branches. This must naturally be the 
case, since the risers must carry all the 
current, the mains divide the current 
among themselves, and the branches carry 
only the current of the few lamps wired 
upon them. We may imagine that each 
lamp has a certain size of wire connected 



252 ELECTRIC INCANDESCENT LIGHTING. 

with it from the street mains, direct to the 
socket, and, that since these wires run side 
by side, they may be regarded as collected 
into a single larger wire, such as a main or 
riser. 

The smallest size of wire which is per- 
mitted to be used in wiring a building, 
in the United States, is No. 18 A. W. G. 
wire, having a diameter of 0.040". 

The wiring of a building should be de- 
signed in such a manner, that when all the 
lamps are burning at any one time, the drop 
in pressure between the street mains and the 
most distant lamp shall not exceed a cer- 
tain small percentage, usually three per 
cent. This drop is calculated by deter- 
mining the total amount of current in 
amperes which will pass through the vari- 
ous mains, sub-mains and branches, deter- 



HOUSE FIXTURES AND WIRING. 253 

mining for each such a resistance as will, 
when carrying this current, produce drops 
of pressure, the maximum sum of which 
along any line shall not exceed the re- 
quired percentage. 

In very large buildings, a feeder system is 
sometimes employed ; that is to say, the 
service wares are connected by feeders 
to centres of distribution, from which 
mains extend both upward and down- 
ward. 

Two supply wires, carrying the full lamp 
pressure between them, are never per- 
mitted to remain in contact with each 
other, even though both are insulated, 
except in cases of flexible conductors, 
which are in plain view and which never 
carry, under normal circumstances, a pow- 
erful current. 



254 ELECTRIC INCANDESCENT LIGHTING. 

Insulated wires are never allowed to 
come into contact with concealed wood- 
work, but when passing through wooden 
beams or floors should be protected by in- 
sulating tubes of porcelain or hard rubber. 

There are three methods of carrying 
out interior wiring; namely, 

(1) Cleat work. 

(2) Moulded work. 

(3) Concealed work. 

Cleat work is the simplest and cheapest, 
but least ornamental type of wiring. The 
wires are carried in insulating receptacles, 
of wood or porcelain, in plain view on the 
ceilings or upper part of the walls. The 
wires should never rest directly upon the 
walls or ceilings, but should be supported 
by the cleat, a full half inch away from 
the same. 



HOUSE FIXTURES AND WIRING. 255 

Fig. 74, shows two forms of wooden 
cleats. Fj f] are the front pieces which 








FIG. 74. WOODEN CLEATS. 



clamp the wires, and B B, are the brackets 
which support the wires free from the 



256 ELECTRIC INCANDESCENT LIGHTING. 

walls. S Sj are the screw holes by which 
the cleats are secured in place and clamped 
together. The wires of opposite polarity 
are always separated by such cleats to a 




FIG. 75. FORM OF SCREW CLEAT. 

distance at least 2 1/2" apart. Cleat work 
is only suitable for indoor work in dry 
localities. Figs. 75 and 76 show forms of 
screw cleats employing respectively wood 
and glass insulation around the wire. 



HOUSE FIXTURES AND WIRING. 



257 



Moulded work is more expensive than 
cleat work, but presents a more sightly ap- 
pearance. Fig. 77, shows different forms of 
three-wire moulding, suitable for different 




FIG. 76. FORM OF SCREW CLEAT. 

sizes of conductor. The moulding is made 
in two parts ; namely, the base or mould, 
with the grooves formed in it, and the 
upper part, or capping, which covers the 
mould. These moulds and cappings are 



258 ELECTRIC INCANDESCENT LIGHTING. 

usually made of soft pine, and are cut into 
lengths of about ten feet. The moulds are 









FIG. 77. SECTIONS OF MOULDINGS. 

first screwed in position on the walls or 
ceilings ; the wires are then laid in them, 
and, finally, the cappings are secured by 



HOUSE FIXTURES AND WIRING. 



259 



screws over them, care being taken not to 
injure the conductors in screwing on the 
cappings. The mouldings are usually 





FIG. 78. PICTURE AND ORNAMENTAL MOULDING. 

painted of a color to conform with the 
ornamentation of the walls or ceilings on 
which they rest. Fig. 78, represents at P y 



260 ELECTRIC INCANDESCENT LIGHTING. 

a form of moulding suitable for hanging 
pictures around the walls of a room, and 
at 0, a type of ornamental moulding. 

The most difficult problem connected 
with the distribution of wires by moulding, 
lies in the connection of the electroliers 
with the wires in the passages without 
presenting an unsightly appearance. This 
is sometimes accomplished by the use of 
dummy moulding, or ornamental mouldings 
symmetrically arranged on the ceiling from 
the centres of the electrolier, in one only of 
which mouldings the wires are placed. 

The best solution of the problem of 
avoiding the unsightly appearance of wires 
is obtained by concealed work, where the 
conductors are buried under floors or in the 
walls and ceilings. This method should 
not be adopted unless the wires besides 



HOUSE FIXTURES AND WIRING. 261 

their insulating cover, are provided with 
a moisture-proof sheet or tube of papier- 




FIG. 79. INTERIOR CONDUITS. 

mache or metal. Such protecting tubes 
form in reality a conduit employed inside 



262 ELECTRIC INCANDESCENT LIGHTING. 

the building and generally called an 
interior conduit. 



Interior conduits may be made in a 
variety of ways, one of which is shown 
in Fig. 79. Conduits made of tubes of 
papier-mache are soaked in a bituminous 



m 




FIG. 80. BRASS-COVERED CONDUIT. 

solution, which serves the double purpose 
of rendering them insulating and practi- 
cally water-proof. Moreover, when house 
wires are carried through a complete 
system of interior conduits, the wires can 
be withdrawn and replaced at any time 
without disturbing the walls or ceilings. 
Fig. 80, shows a conduit tube sheathed 
with a thin layer of brass so as to be 



HOUSE FIXTURES AND WIRING. 



263 



water-tight. Fig. 81, shows a brass tube 
joint connecting different lengths of con- 
duit. Aj is a joint for connecting ordinary 
conduit, and B, a joint connecting brass- 
covered sheathed conduit. Where several 





FIG. 81. INTERIOR CONDUIT JOINTS. 

conduits are united together, a junction box 
is provided containing a number of outlets, 
corresponding with the number of conduits 
as shown in Fig. 82. These boxes are 
closed by a metallic cover. Fig. 83, shows 
two forms of connecting boxes for holding 



264 ELECTRIC INCANDESCENT LIGHTING. 

joints between the mains and branches of a 
two- wire or three-wire system running in 





FIG. 82. INTERIOR CONDUIT JUNCTION BOXES. 

interior conduits. The branch wires in 
this case proceed from the box through 
the smaller apertures. In cellars the con- 



HOUSE FIXTURES AND WIRING. 



265 



duits are frequently heavily sheathed with 
brass or iron. 





FIG. 83. CONNECTION Box FOH INTERIOR CONDUITS. 

The cost of wiring a building depends 
in a great measure upon the number of 



266 ELECTRIC INCANDESCENT LIGHTING. 

outlets required, that is on the number 
of points at which the wires must be 
brought out for connection to switches and 
lamps. Where the lamps are installed in 
groups, as in electroliers, fewer outlets are 
required and the cost is less than if the 
lamps were installed singly. 

Concealed work is generally much more 
readily and cheaply installed during the 
construction of a building than at a sub- 
sequent period. It has become customary 
in large cities to wire all new buildings, 
even though no arrangement has been 
made to supply them immediately with 
electric current. In some cases interior 
conduits are placed in a new building with 
the intention of subsequently wiring the 
building. 

It is often convenient to be able to turn 




G. 267 

some dis- 
(Ts purpose, be- 
sides the key frequently provided in the 
socket for turning on or oft* the individual 
lamp, lamp-switches are placed in the 
branches, or in the mains, whereby all the 
lamps supplied by said branches or mains 
may be lighted or extinguished at once. 
The size and character of the lamp switch 
will depend upon the current strength it 
is intended to control. Switches may be 
divided into two general classes ; namely, 
single-pole switches and double-pole switches. 
In a single-pole switch, as the name indi- 
cates, the connection is broken on one side 
only of the two supply conductors; in a 
double-pole switch, it is broken on both 
sides. Switches are made in a great 
variety of forms, a few of which are illus- 
trated in the accompanying figures. Fig. 
84, shows a form of simple single-pole 



268 ELECTRIC INCANDESCENT LIGHTING. 

switch. By turning the key K, the spring 
/S Y , is brought into contact with the supply 
spring P, thereby ensuring the closing of 
the branch circuit of the lamp through the 




FIG. 84. SIMPLE FORM OP SINGLE-POLE SWITCH. 

switch terminals A and B. Single-pole 
switches should never be employed, except 
for a small number of lamps. Fig. 85, 
shows a different type of switch. $, being 
a single-pole switch, with two terminals, 
and Dj a double-pole switch with four. 



HOUSE FIXTURES AND WIKING. 269 

s 





FIG. 85. SINGLE- AND DOUBLE-POLE SWITCHES. 

In the latter case, two of these terminals 
are connected with the branch wires and 
the other two with the supply mains. 



270 ELECTRIC INCANDESCENT LIGHTING. 

Fig. 86, shows a larger form of double-pole 
switch, intended for a comparatively large 
number of lamps, say 100. Generally, care 




FIG. 86. LARGER FORM OF DOUBLE -POLE SWITCH. 

is given to make the contacts of considera- 
ble surface area, in order that no undue 
heating may arise from imperfect contact. 
Fig. 87, represents a different type of 



HOUSE FIXTURES AlSTD WIRING. 




PIG. 87. DOUBLE-POLE SWITCH. 



272 ELECTRIC INCANDESCENT LIGHTING. 

double-pole switch. Here the turniDg of 
the handle forces a lever into or out of a 
groove, whereby the contact pieces, A B 
and CD, are either insulated or are con- 
nected together. 

Fig. 88, represents a form of switch 
which is sunk into the wall, so that its 
plane outer surface is flush with the sur- 
face of the wall. The switch is, therefore, 
usually called a flush switch. 

In normal operation, the current which 
passes through the conductors in a build- 
ing is only that which is necessary to sup- 
ply the high resistance lamps connected 
with them. If, however, an accidental 
short-circuit, or direct connection, were to 
take place between the positive and nega- 
tive mains in any part of the building, the 
supply wires connected with those mains 



HOUSE FIXTURES AND WIRING. 273 

would be apt to receive a rush of current 
that might render them white hot. In 
order to prevent the danger arising from 
this overheating, a form of automatic 




FIG. 88. FLUSH SWITCH. 

switch has been designed, which im- 
mediately opens the overloaded circuit, 
and thus interrupts the current. The 
automatic switch invariably employed in 
incandescent mains is quite simple in its 
construction and operation. It is called 



274 ELECTRIC INCANDESCENT LIGHTING. 

a fuse cut-out, or safety fuse, and consists 
essentially of a strip or wire of lead, or 
fusible alloy, interposed in the circuit. 
The area of cross-section of the fuse strip 
is such that, while it will readily carry the 
normal current intended to be supplied by 
the conductors with which it is connected, 
it will immediately fuse on the passage of 
an abnormal current. 

Fig. 89, shows a form of branch cut-out; 
i. e., a fuse block inserted between a pair 
of branch wires and the mains supplying 
them. These branch Hocks consist of a 
glazed porcelain base, provided with two 
grooves in which are four terminals A, B, 
O and Dj one pair of which, say A and B, 
are connected to the branch wires, while 
the other pair, O and D, are connected to 
the mains. A, is connected to 6 y , and B, 
to Z>, through two strips /SJ S 9 of fusible 



FIXTURES AND WIRING. 275 

alloy, clamped at the ends under smaller 
screws, as shown. A suitable porcelain 




FIG. 89. BRANCH BLOCK. 



cover is screwed over the whole, so that 
the fuse is completely protected. If the 
current passing into the branch wires be- 



276 ELECTRIC INCANDESCENT LIGHTING. 

comes dangerously strong, the fuses S, S 9 
are melted or blown, and thus automatically 
interrupt the branch circuit. 

Various forms of fuses are employed. 
A common type is represented in Fig. 90. 
Here the fuse consists of lead-alloy wire 
inserted in a small glass plug P, somewhat 
resembling the socket of a lamp. This 
plug screws into receptacles in the cut-out, 
in such a manner that when a fuse is 
melted or blown, it is only necessary to 
remove the plug and screw in a new one. 
The forms of cut-out shown are designed 
for use in connection with two-wire or 
three-wire mains. 

A complete system of house wiring 
includes a number of fuses. Large fuses 
are inserted in the service wires, where 
they enter the cellar, these being usually 



HOUSE FIXTURES AND WIRING. 277 






FIG. 90. PLUG CUT-OUTS. 



called the main fuses. The main cut-out 
fuses are usually placed close to a main- 
switch, where the current can be turned 



278 ELECTKIC INCANDESCENT LIGHTING. 

on or off from the house at will. All con- 
nections between risers and mains, or 
between mains and -sub-mains, or sub-mains 
and branches, are usually provided with 
fuse cut-outs of the size corresponding to 
the current which they have to carry. In 
the circuits of the various fixtures small 
fuses are frequently inserted. Fig. 91, 
represents a few types of such fixture cut- 
outs, as they are called, shaped to conform 
with the fixtures for which they are 
intended. If a short circuit should take 
place, close to an individual lamp, the 
small fuses in the lamp circuit would melt, 
either at the fixture cut-out, or at the 
branch cut-out supplying the same. If a 
short circuit take place in a sub-main, the 
fuse at the junction between the main and 
sub-main would likewise melt, while 
finally, if a short circuit should occur in 
one of the larger mains, the fuses in the 



PRCPERTY CF i 



CHOUSE FIXTURES AND 




279 






FIG. 91. FIXTURE CUT-OUTS. 

main cut-out, where the service wires enter 
the building, would, probably, be instantly 
blown. 



In all large installations, it is important 



280 ELECTRIC INCANDESCENT LIGHTING. 

to be able to detect quickly the location of 
a melted fuse in order that it may be 




FIG. 92. DISTRIBUTION Box. 

replaced and tlie extinguished lamps 
restored as soon as possible. This is fre- 



HOUSE FIXTURES AND WIRING. 



281 



quently done by collecting all the fuses 
belonging to some particular portion of 
the system at a point called a distributing 




FIG. 92A. DISTRIBUTION Box. 

point, usually at a junction of risers and 
mains, or mains and sub-mains. The in- 
take wires ; i. e., those which feed the box, 
are usually brought to a pair of metal bars 



282 ELECTRIC INCANDESCENT LIGHTING. 

in a box called a distribution box lined 
with some fire-proof material let into the 
wall. The out-put wires; i. e., those which 
take their supply from the box, are at- 
tached to separate terminals which main- 
tain connection with the metal strips, 
through safety fuses of the proper size. 

Figs. 92 and 9 2 A, illustrate a particular 
form of distribution box, which is let flush 
into the wall and lined with fire-proof mate- 
rial. A B, are the two intake wires. This 
box is intended for use in connection with a 
two- wire system. A, is placed in electric 
connection with the metal strip g li, and B, 
with the metal strip & Z, through two safety 
fuses. The out-put wires are a b, c d and 
ef; a, c and e, being positive and b, d and/, 
negative. These wires are all placed in elec- 
tric connection with their respective strips, 
each being provided with a safety fuse, as 



HOUSE FIXTURES AND WIRING. 283 

shown, s, s, s, are three switches, for con- 
trolling their independent circuits. Fig. 
92 A shows the box with its cover in posi- 
tion, but with the door opened. At the 
top of Fig. 92 is a cross-section of the box. 
In many cases these boxes have glass doors 
through which the condition of the fuses 
can be readily inspected. 



CHAPTER XIII. 

STREET MAINS. 

IN small towns, systems of incandescent 
distribution are effected by means of over- 
head wires or overhead main conductors; 
that is to say, both feeders and mains are 
insulated wires supported on poles. This 
method of construction is adopted, both on 
the score of economy and the ease of inspect- 
ing, repairing and connecting the Avires. 
In large cities, however, where the number 
of such conductors is necessarily greatly 
increased, and where, moreover, multi- 
tudinous conductors are required for other 
than electric-lighting systems, the wires 
are, to a greater or less degree, necessarily 
buried underground. 



STREET MAINS. 285 

Three methods are applicable to under- 
ground conductors ; namely, subways, con- 
duits and tubes. Of these methods, the first 
two provide means whereby the wires can 
be replaced or removed with greater or less 
readiness. By the third method, the tubes 
are actually buried in the ground and need 
excavation for examination or repair. 

A subway differs from a conduit, in that 
it consists of an underground tunnel of 
sufficient dimensions to permit the passage 
of a man. Underground subways, unques- 
tionably provide the readiest means for 
operating an extended system of con- 
ductors. There are, however, two serious 
difficulties that lie in the way of their 
extensive adoption ; namely, expense, and 
want of room. In our larger cities, an 
unfortunate lack of uniformity has existed 
in the mode of use of the space beneath 



286 ELECTRIC INCANDESCENT LIGHTING. 

the streets, and pavements, for the location 
of the sewer, gas and water-pipes, steam 
heating pipes, and the various systems of 
electric conductors which are to-day so 
imperatively needed in a modern city. 
Unfortunately, in too many cases, the 
location of these lias been placed under 
the control of different and frequently 
antagonistic officials. A lack of space has 
consequently resulted, so that in most of 
our large cities, the construction of a sub- 
way system would require an entire recon- 
struction of the systems of sewers, water, 
gas and electric mains. 

Where a subway is employed, it is 
necessary to ensure its complete drainage 
and also to provide for an efficient system 
of ventilation, whereby the accidental 
leakage of gas into the subway shall not 
produce explosive mixtures with air. 



STREET MAINS. 287 

The conduit affords a much readier and 
more easily applied system for under- 
ground mains or conductors. A conduit 
differs from the subway in that it merely 
provides a space for the wire or cable. 
Various forms of conduits have been 
devised, but all consist essentially of 
means whereby tubes, intended for the 
reception of cables, and generally of some 
insulating; material, are buried in the 

o / 

ground. They are provided with man- 
holes, or a free space in the street, extend- 
ing below the level of the conduits, 
large enough to admit a workman. 
When it is desired to introduce a wire 
into a conduit, or to replace an injured 
wire, the wires are drawn into or from 
the conduits at the manholes. 

Figs. 93 and 94, illustrate in section a 
conduit formed of creosoted wood, laid 



288 ELECTRIC INCANDESCENT LIGHTING. 

together in sections, so as to leave cylin- 
drical spaces between them, through 
which the wires or cables may be drawn. 
This system is frequently used for the 




FIG. 93. CONDUIT OP CREOSOTED WOOD. 

reception of lead-covered high-tension 
wires, and telephone cables. 

While overhead conductors may be un- 
objectionable in small towns or villages, 
yet, in large cities, where the need for 
wires is great and, moreover, is con- 



STREET MAINS. 289 

stantly increasing, a condition of affairs 
might readily be brought about such as 
is shown in Fig. 95, which represents 
the condition of a street with the 




FIG. 94. CONDUIT OF CREOSOTED WOOD CUT AWAY TO 
SHOW STRUCTURE. 



many aerial wires that are to be ex- 
pected. Contrast this with the altered 
appearance of the same street, when the 
wires were placed in underground con- 
duits as shown in Fig. 96, and the advan- 
tage of underground wires, from an aesthetic 
standpoint, is manifest. 



290 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 95. VIEW OP CITY STREET WITH OVERHEAD WIRES. 



STREET MAINS. 291 




FIG. 96. VIEW OF CITY STREET AFTER REMOVAL OF 
OVERHEAD WIRES. 



292 ELECTRIC INCANDESCENT LIGHTING. 

Fig. 97, represents the third method for 
underground conductors, viz.; the under- 
ground tube. Here an iron pipe is em- 
ployed, containing three insulated conduc- 
tors, and intended for use in a three- wire 

J 



FIG. 97. TUBE CONTAINING THREE SEPARATELY 
INSULATED CONDUCTORS. 

system of distribution. The iron pipe is 
provided for the purpose of protecting the 
conductors from mechanical injury. Fig. 
98, shows cross-sections of different sizes 
of these tubes. A, B and C, are the cross- 
sections of the copper conductors, sur- 
rounded and supported by a bituminous 
insulating material. The outer ring is the 
section of the iron pipe. 

As the above form of underground tube 
is to-day in extended use, a description of 



STREET MAINS. 293 

its manufacture will not be out of place. 
The iron pipes are made up in lengths of 
twenty feet. The copper conductors, cut 
off to the right length, are prepared for 




FIG. 98. MAIN TUBES. 

placing in the tube by wrapping each 
with a loose or open spiral of rope. 
Three rods are then assembled and held 
together, in the position shown in the 
cross-section, by wrapping them with a 
tight wrapping of rope. The rods so 
assembled, are now placed in a length of 
tube, and one end of the tube is closed 



294 ELECTRIC INCANDESCENT LIGHTING. 

with a plug. The tube is then filled 
with hot bituminous insulating material. 
The tube is finally closed by a second 
block. There will thus be provided, 




FIG. 99. SECTION OP STREET TRENCH CONTAINING A 
FEEDER AND MAIN TUBE. 

lengths of pipe twenty feet long, con- 
taining three insulated conductors with 
their extremities projecting at the ends. 

The underground tubes so formed are 




// 295 

V5> h 

Y- // 

sent dBJbCftoni the factory in c me r ' twenty - 

T^>! 4*' f f ?v-r~M^ ' r 

foot sectionfeteseril)ed. They are subse- 

/ 

quently connected to one another, while 
in position in the underground trench 
prepared to receive them. Fig. 99, shows 
a section through a trench provided for 
a feeder and a main tube. The trench 
is usually 30" deep, as shown, and is 
situated in the street a short distance 
from the curb, the pipes being laid end to 
end at the bottom of the trench. 



It now remains to connect the separate 
lengths of the underground tubes. For 
this purpose coupling boxes are provided 
as shown in Fig. 100. A, shows a coup- 
ling box suitable for a street connection, 
and B, a coupling box for a right-angled 
connection. The coupling box is formed 
of a cast iron shell made in halves, 
connected together by bolts passing 



296 ELECTRIC INCANDESCENT LIGHTING. 

through flanges, and clamped over collars 
secured at the ends of the tubes. The 




FIG. 100. COUPLING BOXES. 

collars are first secured in place. The 
lower half of the box is then fitted and 
the three flexible copper stranded con- 



STREET MAINS. 297 

nectors are forced on the ends of the con- 
ductors as shown. By the aid of a torch, 
the joints are all heated to a sufficiently 
high temperature, and solder is melted 
into them, thus forming a good metallic 
junction. The upper half of the box is 
then fitted into place, the two parts 
clamped together by the bolts, and melted 
bituminous compound is poured into the 
box through an aperture in the top. The 
coupling box is then closed as shown at J 
in Fig. 97. 

Fig. 101, shows a form of branch coup- 
ling box suitable for a house-service con- 
nection with the mains. In this case, A. 
and B, are main tubes passing along the 
street, while C\ is the house service tube. 
Here the coupling box is shaped to con- 
form to the requirements of the triple 
connection as shown. 



298 ELECTRIC INCANDESCENT LIGHTING. 

Fig. 102, shows cross-sections of feeder 
tubes. In these tubes, the neutral con- 
ductors are of smaller size than the two 
outside conductors, since the system is 




FIG. 101. BRANCH COUPLING Box. 

arranged to be nearly balanced as to load 
with reference to the neutral. The three 
small black wires shown, are called pressure 
wires; i. e., small insulated copper con- 
ductors which are returned from the feed- 
ing point, or point of junction between 



STREET MAINS. 299 

feeder and mains, to the central station, so 
as to indicate in the central station, the 
pressure which is supplied to the mains. 
Thus, if the drop in the feeders, be say 15 




FIG. 102. FEEDER TUBES. 

volts, and the pressure at the bus-bars, in 
the central station, be 130 volts on each 
side of the system, or 260 volts across out- 
side bus-bars, the pressure in the mains at 
the feeding point will be 115 volts on each 
side, and this will be the pressure carried 
by the small pressure wires back to the 
indicators at the central station. 



300 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 103. JUNCTION Box. 



Fig. 103, shows the interior and Fig. 104, 
the exterior of a junction box ; i. e., a box 
situated at the junction of two streets, or 



STREET MAINS. 301 

at a feeding point where a feeder joins the 
mains. This box is of cast iron, and is 
buried with its surface flush with the 
street level. The tubes enter the sides of 




FIG. 104. JUNCTION Box. 

the box at the lower level. The conduct- 
ors are connected by flexible connections 
with brass pieces supported on insulating 
rings. These pieces are marked + and - 
according to the polarity of the conductors 
connected with them. 



302 ELECTRIC INCANDESCENT LIGHTING. 

Three metallic rings, insulated from eacli 
other, are provided in the box corresponding 
to the three conductors in the tubes. All 
the positive conductors are connected across 
to the positive ring, through fuse strips ; all 
the negative conductors are connected to 
the negative ring ; and all the neutral con- 
ductors, to the neutral ring. In this way all 
the positive conductors are placed in elec- 
trical connection with each other, and also 
the negative and neutral conductors. The 
box is made water-tight by lowering a 
cover over the bolts seen in the ring in the 
upper part, screwing down nuts upon 
these bolts, and pouring in bituminous 
compound in a melted state over the bolts. 
J?, is a feeder tube containing the pressure 
wires and five conductors, a pair of nega- 
tives, a pair of positives, and a neutral. 
MM, are main tubes ; p, is a slab or strip 
of insulating material, supporting the con- 



STREET MAINS. 

nections for the pressure wires, which are 
connected through fuses with the three 
rings in the box. Fig. 104, shows the 
appearance of the junction box when closed 
with an ornamental cover. 



CHAPTER XIV. 

CENTRAL STATIONS. 

IF we could follow the buried conduct- 
ors through the streets, up-stream, that is, 
toward the supply, we would finally reach 
a building toward which all these wires 
converge. This building constitutes what 
is called a central station. In it we will 
find the means for generating the current 
which is sent through the street mains and 
feeder wires, through the service conduct- 
ors into the house, and finally through the 
risers and house mains and branches, to 
the lamps. Limiting our description of 
the station to one in which continuous 
electric currents only are generated; i. e., 



304 



CENTRAL STATIONS. 305 

currents which always flow in the same 
direction, and which are suitable for use in 
the three-wire system of buried conductors 
just described, and supposing, as is gener- 
ally the case, that steam power is employed, 
we will find that the apparatus can be 
readily grouped into three general classes ; 
namely, 

(1) The dynamos. 

(2) The engines. 
(a) The boilers. 

Directing our attention in the station 
first" to that part of the building at which 
the feeders enter from the street, we will 
find them connected to a device called a 
switchboard. This consists essentially of a 
fire-proof frame supporting a number of 
metallic terminals provided for connection 
with the feeders and also with connections 
designed to receive conductors from the 



306 ELECTRIC INCANDESCENT LIGHTING. 

generators. A number of instruments are 
mounted on this switchboard, consisting of 
ammeters to show the strength of current, 
and voltmeters to show the pressure on the 
various feeders, while switches are pro- 
vided for opening and closing the various 
circuits. 

Fig. 105, shows a partial view of a 
switchboard in a central station. /SJ /S 7 , S, 
are rows of massive switches mounted 
upon fire-proof slabs of insulating material. 
Above the switches are the voltmeters and 
ammeters, while at F, are the field regulat- 
ing boxes for controlling the pressure of 
the generators. During the daytime, the 
load on the mains is principally due to 
motors arid is considerably less than the 
night load. As evening approaches, the 
load increases, as is shown on the ammeters 
at the station. As soon as it becomes 




PRCFCRTY OF 




308 ELECTRIC INCANDESCENT LIGHTING. 

necessary to introduce another pair of 
dynamos, the engine driving them is 
started, the pressure of the dynamos is 
brought up to that required, and the 
switches are then closed at the switch- 
board, thus connecting the new generators 
with the feeders. The reverse process is 
adopted as the load diminishes, and it is 
unnecessary to any longer maintain the 
extra generators in the circuit. 

Fig. 106, shows a type of generator unit 
frequently met with in large central 
stations, for low-pressure incandescent-light 
distribution. This figure represents a por- 
tion of the engine room in a large central 
lighting station, and shows two generator 
units at A and B, respectively. A, is a 
vertical condensing, triple-expansion engine, 
Ej E, E, whose main horizontal shaft 
drives at each end the armature of a dy- 



310 ELECTRIC INCANDESCENT LIGHTING. 

namo or generator 6r, to be presently 
described. This engine has two platforms 
P, P. This engine runs at 120 revolu- 
tions per minute, developing a maximum 
of 800 HP; or, approximately, 600 KW, 
the two generators being of 200 KW 
capacity each. At B, is a smaller generat- 
ing unit of similar construction, provided 
with a single platform />, and. also driving 
two smaller dynamo armatures, each of 100 
KW capacity, the maximum out-put of the 
engine being 300 KW, or about 400 HP, 
at 172 revolutions per minute. 

It is evident, under these circumstances, 
that when the engine is developing its full 
load, the dynamos will be overloaded about 
forty per cent. Owing to the fact that 
the full load on a central station is of short 
duration, this has been found to be an 
economical practice. 



CENTKAL STATIONS. 311 

In order to provide power to drive the 
engines and dynamos a battery of boilers 
is installed. Boilers are of various types. 
Since an incandescent lamp requires an 

activity of 50 watts, or about tpth of one 

horse-power at its terminals, and since 
losses occur in the feeders, mains and 
house wires of, perhaps, ten per cent, on 
an average, the activity per lamp at the 
dynamo terminals, in a central station, will 
be about 55.5 watts. Moreover, since an 
average loss of say fourteen per cent, 
occurs in the engine and dynamo, the 
activity per lamp, generated by the engine, 
must be about 64.5 watts, or about the 

T^th of a horse-power, so that on an aver- 

1 l.D 

age, one indicated horse-power at the 
engine, represents 11.5 sixteen-candle power 
incandescent lamps of 50 watts each. In 



312 ELECTRIC INCANDESCENT LIGHTING. 

other words, the average commercial effi- 
ciency of such a system of distribution, 
starting from the indicated horse-power 
of the engine, is, approximately, 77.5 per 
cent. About 17 pounds of steam, at 160 
pounds pressure, are required per indicated 
horse-power-hour with engines of the type 
shown. This represents about 2.9 pounds 
of coal per horse-power-hour delivered 
electrically in consumers' lamps. 

A large central station may readily sup- 
ply 60,000 incandescent lamps or more. 
Assuming that 60,000 is supplied at maxi- 
mum load, the boiler power needed will be 
correspondingly great. Take, for example, 
the central station that was required to 
supply the buildings and grounds of the 
World's Columbian Exhibition at Chicago, 
in 1893, with electric light. There were 
employed for lighting this exhibition, 



CENTRAL STATIONS. 313 

about 100,000 incandescent lamps and 
about 5,000 arc lamps. There was 
naturally required for this purpose, as 
well as for driving the machinery in the 
buildings, a very great amount of power. 

Fisf. 107, shows a view of the main 

O ' 

boiler plant in the above exhibition. Here 
batteries of boilers, representing an aggre- 
gate of 24,000 horse-power are shown. 
_/), Z>, are the main doors, d, d, the fire 
doors, and beneath these latter the ash-pit 
doors. 6r, is the steam gauge to show the 
steam pressure in the boiler above that of 
the atmosphere ; g, the water gauge ; M, the 
steam drum, and P, the main steam pipe. 

To the student of the incandescent 
lamp, the most important features of the 
central station are the dynamos or genera- 
tors designed to supply the current to the 



314 ELECTRIC INCANDESCENT LIGHTING. 

lamps. Limiting our attention now to 
continuous-current dynamos, we will find 
these to be of a variety of types, although all 
operate on essentially the same principle. 

Broadly speaking a dynamo-electric ma- 
chine or generator, is a device whereby 
electromotive forces, and from these, elec- 
tric currents are produced, generally by 
the revolution of conductors through 
magnetic flux. The magnetic flux is pro- 
duced by field-magnet coils. E. M. Fs. are 
set up in the coils on the revolving por- 
tion, called the armature. These E. M. 
Fs. are generated in the armature coils 
in successively opposite directions, as they 
pass each pole ; consequently, they need 
to be commuted, or caused to assume the 
same direction in the external circuit. 
This is effected by a device called a com- 
mutator. 



316 ELECTRIC INCANDESCENT LIGHTING. 

Thus Fig. 106, represents muJMpolar 
generators, there being fourteen magnets or 
poles Jt/J Mj My on the large dynamo, and 
eight magnets or poles, on the small dynamo. 
These magnets form part of the massive 
stationary iron frames F F F,f f f, sup- 
porting the outboard bearings O, o. In 
the cylindrical bore of these field-magnet 
poles, run the armatures, which are rigidly 
secured to the main engine shaft. A light 
metallic frame supports a number of pairs 
of brushes B, B, upon the surface of the 
commutator, there being as many pairs of 
brushes as poles, so that A, has fourteen 
pairs of brushes upon its commutator and B, 
has eight pairs. These pairs of brushes, or 
double brushes, as they might be called, are 
insulated from their supporting frame, but 
are connected in alternate pairs with the 
main terminals T, T. Thus the first, third, 
fifth, etc., brushes are connected to one 



CENTRAL STATIONS. 317 

terminal, and the second, fourth, sixth, etc., 
with the other. H, h, are handles for rock- 
ing the entire brush-holder frame to-and- 
fro within a small angular range around 
the axis, so as to cany all the brushes for- 
ward or backward upon the surface of the 
commutator. This adjustment is made 
to prevent sparking at the brushes from 
the current which they carry at different 
loads. The main terminals T, T, are con- 
nected to switches on the main switch- 
board of the station. 

Fig. 108, shows in greater detail another 
form of central station generator of the 
same type. F, F, F, is the field frame. 
M, M, M y are the field fcoils, six in num- 
ber, consisting of coils of insulated wire 
wound upon soft steel cores bolted radially 
to the field frame, as shown. A., is the 
armature whose surface runs within the 



318 ELECTRIC INCANDESCENT LIGHTING. 

cylindrical polar space formed by the poles 
of the field magnets. (7, C, is a commu- 




FIG. 108. SIX-POLE GENERATOR. 

tator, consisting of copper strips, rigidly se- 
cured in a cylindrical frame, and insulated 




from one anotl;fc:^^ 
conducting loops wound upon the arma- 
ture. 13, It, are the brushes, of which there 
are six pairs, connected to two metallic 
rings, one ring being in connection with 
three alternate pairs. These rings are 
finally connected to the main terminals T, 
Tj by cables, as shown. The current sup- 
plied by the armature is collected by each 
brush, leaving the armature at the three 
positive brushes, and, after traversing the 
external circuit of the feeders, mains, 
house wires and lamps, returning to the 
armature through the three negative 
brushes, thereby completing the electric 
circuit. H, is a handle for advancing or 
retreating the brushes over the surface of 
the commutator. The machine shown has 
50 KW capacity, that is to say, it will 
deliver at its terminals activity to the 
amount of 50 KW, (400 amperes at a 



320 ELECTRIC INCANDESCENT LIGHTING. 

pressure of 125 volts, or 400 X 125 = 
50,000 watts). It requires about 75 
horse-power or about 56 KW to drive it 
at full load. Its gross weight is 6,500 
pounds, representing an output of, approxi- 
mately, 7.7 watts per pound of total 
weight. It has a shaft five inches in di- 
ameter, and occupies a space of 30" X 61" 
X 51" in height. 

The armature of the preceding machine 
is illustrated in greater detail in Fig. 109. 
It consists of a metal cylinder, which car- 
ries on its outer surface a laminated iron 
core, built up of annular sheet-iron discs, 
clamped side by side, so as to form, when 
assembled, an almost complete cylindrical 
external surface of iron, A A. Gaps are 
left, at suitable intervals between adjacent 
sets of discs, to provide for the ventila- 
tion of the armature, by means of the pas- 



CENTRAL STATIONS. 



321 



sage of air by centrifugal force from within 
outward, to aid in the cooling of the ar- 




FIG. 109. ARMATURE OF GENERATOR. 

mature, when operated. The outer sur- 
faces of the iron discs are provided with 



322 ELECTRIC INCANDESCENT LIGHTING. 

longitudinal slots, parallel to the axis of 
rotation. These slots are designed to re- 
ceive the armature conductors. One hun- 
dred and sixty-eight of these slots are thus 
provided to receive one hundred and sixty- 
eight sets of conductors. 

The winding adopted in the armature is 
conducted as follows : At A, a pair of 
rods or wires comes through a slot across 
the armature surface. A pair of flexible 
copper strips, insulated from their neigh- 
bors, are soldered to the rods at #, and run 
down to b. These connect two adjacent 
commutator bars at b. From this they run 
back behind the connections W, IF, to the 
slot at c, and then across the armature sur- 
face underneath the two rods or wires 
which are seen to approach at c. Having 
reached the opposite side of the armature 
at c' y they descend obliquely on the other 



CENTRAL STATIONS. 323 

face to a point opposite d, and then ascend 
to the armature surface at a point c. Here 
the rods connected therewith return across 
the armature surface to the point 0, de- 
scending again to the commutator at the 
point f. In this manner a pair of con- 
ductors zig-zag across the armature, via 
g i ~k, emerging again one slot in advance 
of a, and so on. In this manner it must 
always happen that the wires in the slot 
a, pass under one pole, the wires c e g i Jc 
will also be passing under the other poles. 
The effect of the commutator is to enable 
the brushes to collect 'all the currents 
which are being generated in the various 
wires passing under the different poles and 
to unite them in the external circuit. 



CHAPTER XV. 

ISOLATED PLANTS. 

FOR the general purposes of house light- 
ing, where comparatively few lamps are re- 
quired, it is more economical for the house- 
holder to rent his electric power from a 
central station, than it would be for him to 
erect and maintain his own plant. Since 
a plant requires boilers and engines, it 
would follow, unless a fairly considerable 
number of lamps is required, that the 
extra expense of the installation as well as 
the services of an engineer, or engineer 
and fireman, would make it much cheaper 
in such cases to take the service from the 
street mains as supplied by the nearest 



ISOLATED PLANTS. 325 

central station. There are many cases, 
however, in which either the number of 
lights, or the circumstances are such, as to 
warrant, in point of economy, the main- 
tenance of what may be called an isolated 
lighting plant, in contradistinction to a 
central-station lighting plant. 

It is clear that when the number of 
lights required reaches a certain limit, it 
may be preferable to maintain an isolated 
plant, rather than to rent the light, since 
a large building or plant would thus 
possess the advantage of being indepen- 
dent of the running of the central station, 
or of accidents which might occur to the 
street mains. Moreover, a large isolated 
plant, being necessarily circumscribed in 
the area of its distribution, would require 
a much smaller outlay or expenditure in 
copper, and, consequently, may be built to 



326 ELECTRIC INCANDESCENT LIGHTING. 

produce light cheaper thaii a central 
station. 

But even in cases where the number of 
lights is not very great, circumstances may 
arise where it would still be economical to 
establish an isolated plant. Such cases 
would be found, for example, in manufac- 
turing establishments, where boilers and 
steam engines have necessarily to be main- 
tained in action during the time that light 
is required. Again, isolated plants arc 
necessary in sections of country remote 
from central stations. A brief description 
of isolated plants for the supply of in- 
candescent lighting will, therefore, be of 
interest. 

Any suitable form of dynamo can be 
used for an isolated plant. The dynamo 
may be driven either directly from the 
engine shaft or by means of leltimj. The 



ISOLATED PLANTS. 



327 



direct connection requires less floor space, 
is somewhat more efficient, and saves wear 




FIG. 110. BELT-DRIVEN GENERATOR FOR ISOLATED 
PLANTS. 



330 ELECTRIC INCANDESCENT LIGHTING. 

of belting, but possesses the disadvantage 
of requiring the engine to run at a com- 
paratively high speed, and the dynamo at 
a comparatively low speed. This means 
that for all sizes of generator below 50 KW 
at least, the cost of a direct-driven plant 
is greater than that of a belt-driven plant, 
because a slow-speed dynamo means a 
heavier and, consequently, a more expen- 
sive dynamo, and a high-speed engine is 
more difficult to maintain in running 
order. 

Fig. 110, represents a bipolar, or two- 
pole, generator, driven by a belt from a 
small vertical engine with its governor 
inside the fly wheel. 

Fig. Ill, represents a quadripolar or 
four-pole direct-driven generator, suitable 
for isolated plants. In this case the en- 



332 ELECTRIC INCANDESCENT LIGHTING. 

gine is completely enclosed in a cast-iron 
shell and runs in oil. 

Fig. 112, represents a type of isolated 
lighting plant employed on board ships and 
supplied to several vessels in the United 
States Navy. This quadripolar generator 
delivers 200 amperes at 80 volts pressure, 
or 16 KW, at a speed of 400 revolutions per 
minute. It is directly connected as shown 
to the vertical marine engine. 

Fig. 113, represents an isolated three- 
wire plant, consisting of a 100-horse-power 
horizontal steam engine, driving two 32 
KW quadripolar generators at a speed of 
270 revolutions per minute. The magnet 
poles in this case are inside the armature 
and the outer surface of the armature has 
its insulated conductors bare, so as to form 
a commutator, upon which the sets of 



ISOLATED PLANTS. 



333 



brushes shown in the figure can rest. 
The switchboard for controlling the vari- 
ous circuits is represented behind the 
machine on the right hand side of the 
figure. The apparatus required for such a 
switchboard is similar in kind to that of 
a central station, but usually is smaller and 
less complex. 




CHAPTER XVI. 

METEES. 

THE sale of any product requires some 
suitable unit of measure. Since electric 
power is undoubtedly a product requiring, 
as it does, the establishment of an expensive 
plant for its production, a unit of measure 
is necessary, as well as an apparatus 
w^hereby the number of units delivered to 
the customer by the producer may be 
measured. 

Various plans have been devised for the 
measurement of electric supply. Of these, 
however, only two forms are in general 
use for the measurement of continuous-cur- 

334 



METERS. 335 

rent supply. One of these forms meas- 
ures the quantity of electricity delivered 
to the consumer in units of supply called 
ampere-hours, while the other measures the 
energy in watt-hours. Each of these forms 
of apparatus is called a meter. 

Fig. 114, shows a form of electrolytic 
meter indicating the supply in ampere- 
hours. This apparatus depends for its 
operation on the fact that an electric cur- 
rent, when sent through a solution of zinc 
sulphate, will effect a decomposition of the 
solution, depositing metallic zinc on a zinc 
plate connected with the negative termi- 
nal, and dissolving or removing an equal 
quantity of zinc, from a plate of zinc con- 
nected with the positive terminal. The 
indications of this meter are obtained by 
carefully weighing the plates, before and 
after the supply they are to measure has 



336 ELECTRIC INCANDESCENT LIGHTING. 

passed through them. After the meter 
has been in use for some time, it will be 
found that the zinc plate connected to the 
positive terminal has decreased in weight, 







FIG. 114. ELECTROLYTIC METER. 

and that connected with the negative 
terminal has increased in weight. This 
difference of weight is a measure of the 
number of ampere-hours that have passed 
through the cell. 



METEES. 337 

In the interior of the meter box, in the 
upper part, are two large strips of ger- 
man silver 7t, J?, carrying the current to 
be supplied to the lamps, and offering a 
definite small resistance to its passage. 
The positive and negative supply wires 
enter the box at P and N, and are se- 
cured to the terminals P and N, inside. 
As the meter shown is a three-wire meter, 
it consists of two meters, in one box, one 
being for the supply on the positive main, 
and the other for the supply on the nega- 
tive main. If the number of lamps 
lighted in a house, on each side of the 
system, were always the same, the records 
of these two meters would be equal. 
When the current passes through the re- 
sistance J5 .7?, it establishes a certain drop 
of pressure, as already explained in Chap- 
ter III. This drop amounts to about 0.4 
volt at full load. In a pair of derived or 



338 ELECTRIC INCANDESCENT LIGHTING. 

shunt circuits, connected across the ex- 
tremities, of each strip of resistance R, is 
placed a pair of small glass bottles with 
resistances wound on a spool s, behind 
them. The total resistance of the bottle, 
or plating bath, and the spool in its circuit, 
bears such a relation to the resistance of 
the shunt R, that each milligramme of zinc 
electroplated on the surface of the nega- 
tive zinc plate 2, represents a definite 
number of ampere-hours of current sup- 
plied through the meter according to its 
size. The plates 2, 2, are made of zinc and 
mercury alloy, and are separated from 
each other by hard rubber washers. 
Copper rods extend upwards from these 
plates through the corks <?, <?, to the 
copper clips p, p. There are two bottles 
for each side of the meter, so that a dupli- 
cate record is kept on each side of the 
supply. It is usual to renew the bottles 



METERS. 339 

once a month. The bottles after being re- 
moved are emptied, the zinc plates washed 
and dried, and weighed in a chemical bal- 
ance, and the amount of the supply deter- 
mined from the difference in weight dur- 
ing the month. The solution employed is 
of pure zinc sulphate in water, having a 
density of 1.11 at 60 F. The advantage 
of this meter is its simplicity, and the fact 
that all its essential working parts are re- 
moved and replaced once a month. The 
disadvantage of the meter, is that it does 
not show directly to the consumer, the 
amount of supply which has been de- 
livered. 

When such meters are placed in ex- 
posed situations, where the solutions might 
be liable to freeze, a thermostat is em- 
ployed to maintain the temperature of the 
bottles above the freezing point. Such a 



340 ELECTRIC INCANDESCENT LIGHTING. 

thermostat is shown in Fig. 115. Here a 
metallic strip, composed of two unequally 
expansible metals riveted together, is so 
arranged, that, when exposed to a suffi- 

p 




FIG. 115. THERMOSTAT FOR ELECTROLYTIC METERS. 

ciently low temperature, the unequal con- 
traction of the metals will cause a bending 
or warping, which will close the circuit of 
a lamp through the set screw s. The 
lamp will then burn until the temperature 
rises sufficiently to allow the strip p p, to 
straighten and break the circuit. 



METEKS. 



341 



Another form of meter in general use is 
shown in Fig. 116. In this form of in- 
strument, the number of watt-hours deliv- 
ered to the consumer is registered. It 




FIG. 116. INTERIOR OF RECORDING WATTMETER. 



342 ELECTEIC INCANDESCENT LIGHTING. 

consists of a small motor, the field magnet 
coils M, M, of which are in the direct cir- 
cuit of supply. The armature A, placed 
within the field coils, revolves upon the 
vertical shaft S 9 8, with a speed propor- 
tional to the activity delivered ; i. e., to the 
product of the volts and amperes. For 
example, if the pressure at the house 
mains be 110 volts, and the current be 2 
amperes, then the activity delivered would 
be 110 X 2 = 220 watts; and, in one hour, 
this rate of delivery would result in a 
supply of 220 watt-hours, while the rotary 
speed of the armature shaft would be pro- 
portional to this value 220. A small com- 
mutator is seen just above the field coils 
with its long slender brushes running 
back to supports behind the apparatus. 
The armature is placed in a circuit of high 
resistance across the mains, so that it ab- 
sorbs a constant small amount of activity, 



METERS. 



343 




FIG. 117. RECORDING WATTMETER. 

whether the meter be running or not. 
The shaft engages by means of an endless 
screw with a pinion wheel, forming part 



344 ELECTRIC INCANDESCENT LIGHTING. 

of a train work of dial-recording median- 

o 

ism, similar, to that of a gas meter. 

The above form of the apparatus, when 
completely enclosed, is seen in Fig. 117. 
The cover is secured to the base by a wire 
sealed with the leaden seal s. The supply 
and output wires pass through the meter 
beneath. The advantage of this meter is 
that it enables the customer to observe 
the amount of power he consumes. Its 
disadvantage is that it constantly absorbs 
a small amount of power. A meter should 
always be installed in a dry place, and 
inserted in the service wires between the 
street main cut-out and the risers. 



CHAPTER XVII. 

STORAGE BATTERIES. 

IF the supply of electric current re- 
quired for incandescent lamps was uni- 
form throughout the twenty-four hours, it 
would be easy to determine the most eco- 
nomical generator units of boiler, engine 
and dynamo, in order to meet this require- 
ment economically. Unfortunately, how- 
ever, in nearly all cases the variations in the 
load are very great. A few hours of the 
twenty -four require a load greatly in excess 
of the average. If, in order to meet this 
load economically, the generating plant be 
subdivided into a number of small units, 
so as to permit them to be readily with- 
drawn and added as required, both the 



345 



346 ELECTRIC INCANDESCENT LIGHTING. 

expense arid the complexity of the gener- 
ating system would be necessarily in- 
creased. If, on the other hand, a large 
generating unit be installed, it would 
have to be operated for the greater part of 
the twenty-four hours at a very small 
load, and, therefore, uneconomically. 

The above difficulty is sometimes met 
by the employment of storage batteries, 
which are charged during the hours 
of light load, and discharged during the 
hours of heavy load, thereby equalizing 
the load on the station. Since, at the 
time of full load, the output is obtained 
both from dynamos and storage batteries, 
it is evident that a much smaller generat- 
ing plant of boilers, engines and dynamos 
is rendered necessary. 

In order to determine whether it would 



STORAGE BATTERIES. 



347 



be economical to install a storage battery, 
it is necessary to ascertain the load diagram 
of the station ; that is, the curve which rep- 
resents the output required to supply the 



FIG. 118. LOAD DIAGRAM. 



lamps during the twenty-four hours of the 
day. Such a load diagram is shown in Fig. 
118. In this figure the hours of the day are 
marked off horizontally, and the current 



348 ELECTRIC INCANDESCENT LIGHTING. 

strength delivered to the feeders is 
marked off vertically in amperes. An in- 
spection of the figure will show that the 
peak of the load, that is, the maximum load 
of the curve, occurred at 5.30 p. M. when it 
exceeds 1,700 amperes, while an hour and 
a half earlier, or at 4 p. M., it was 800 
amperes, and an hour and a half later, or at 
7 P. M., it was 930 amperes. At 8.30 p. M. 
the load has increased, perhaps, owing to 
the lighting of some theatre, after which 
the load steadily falls until 2.30 A. M. The 
average load during the twenty -four hours 
from this diagram is 620 amperes, and since 
the maximum load is 1,710, the ratio of the 
average to the maximum is 0.363 or 36.3 
per cent. This is called the load factor. 

If the load represented in Fig. 118, were 
supplied without the aid of a storage bat- 
tery, it would be necessary to install boil- 



STORAGE BATTERIES. 349 

ers, dynamos and engines to the extent 
necessary to supply a current of 1,700 
amperes, although the average load is only 
620. By the use of a storage battery, 
capable of supplying 800 amperes for, 
say four hours ; or, a battery having 
a storage capacity of 4 x 800 = 3,200 
ampere-hours, then the maximum load 
which the boilers, engines and dynamos 
would have to supply would be 900 
amperes \ or, only about half as much 
as in the preceding case, while the load 
during the daytime would be increased 
by the amount necessary to charge 
the storage batteries. Good practice re- 
quires that the charging be done during the 
time of the day when the load is the least ; 
or, in this case, between the hours of 1 and 7 
A. M. The smaller the load factor the greater 
the probability of obtaining economy in 
the installation of a storage battery. 



350 ELECTRIC INCANDESCENT LIGHTING. 

Another case arises in which an advan- 
tage is derived from the use of a storage 
battery ; namely, where the engines and 
boilers employed to drive the dynamo are 
used during the hours of darkness only, 
and are stopped during the day, while it is 
desired to maintain a few lamps during 
the daytime. Under these circumstances 
it is often more economical to establish a 
storage battery plant, which can be charged 
during the time of running at night, thus 
permitting the engine and dynamo to be 
stopped during the daytime and the stor- 
age battery to supply the few lights 
required. 

Before proceeding to the general descrip- 
tion of a storage battery installation, it 
may be well to describe briefly the princi- 
ples of its operation. A storage cell differs 
in no respect from an ordinary voltaic cell ; 



T *$ 

PHCFLRTY CF 



351 



for, like a^iftaieHgytj^fiafi^^ essentially 
of two plates or elements, called respectively 
the positive and the negative plate, plunged 
in an acid liquid or electrolyte capable of 
acting on one of the plates. As the result 
of the chemical action that occurs under 
these circumstances, an electric current is 
produced which passes in a definite direc- 
tion through the electrolyte and issues from 
the cell at one of its terminals or poles 
and returns to it, after having passed 
through the circuit in which the cell is con- 
nected, by the other terminal or pole. In 
both the ordinary voltaic and the storage 
cell, exhaustion takes place when a certain 
output of electricity is yielded. In the 
case of the voltaic cell both the liquid, and 
at least one of the plates, must be renewed, 
while in the case of the storage cell, all 
that is necessary for renewal is to connect 
the terminals of the cell with an independ- 



352 ELECTRIC INCANDESCENT LIGHTING. 

ent electric source, and send a current 
through it in the opposite direction to that 
of the current it yields. This current is 
called the charging current, and the cell re- 
ceiving it is said to be charged. Since a 
storage cell thus derives its energy second- 
arily from some other electric source, it is 
sometimes called a secondary cell, in contra- 
distinction to a primary or voltaic cell. 

A great number of storage cells have 
been devised. Practically all that have 
been placed in commercial use, consist of 
perforated lead plates or grids, correspond- 
ing to the positive and negative plates of 
the voltaic cell, with the perforations filled, 
respectively, with peroxide of lead and 
finely divided metallic lead. These plates 
are associated, or placed side by side, in a 
solution of sulphuric acid and water. In 
the original form given to these cells, they 



STORAGE BATTERIES. 353 

consisted of a very large positive and nega- 
tive plate, suitably supported at a short 
distance from each other, and then rolled 
up together in a close spiral. It was 
found, however, in practice, that when 
such a plate became damaged in one part, 
the entire cell had to be rejected, so that 
for the purpose of convenience, as well as 
for the ready inspection of the different 
parts of the plate, they are now generally 
made in a number of smaller plane plates, 
placed parallel to one another, which, 
when connected in parallel, are equivalent 
to two large plates of the same total sur- 
face. 

The simplest form of such a cell would 
consist of a single positive and a single 
negative plate, placed side by side ; but 
since the positive plate would only have a 
negative plate on one side of it, the other 



354 ELECTRIC INCANDESCENT LIGHTING. 

side being uncovered, it is preferable to 
associate two negative plates with one posi- 
tive plate, so as to utilize the entire surface 
of the positive plate. Such a cell is shown 
in Fig. 119, where two negative plates, JV", 
are placed one on each side of a single posi- 
tive plate P, inside a jar e7W, filled to 
a convenient height with sulphuric acid 
and water. The positive plate is shown 
separately at A. It consists of a grid or 
frame of antimonious lead ; i. e., lead 
alloyed with a small amount of antimony, 
so as to keep it from being acted upon by 
the acid liquid. In this frame are shown 
eight small circular buttons a, filling circu- 
lar holes in the grid. These, when the cell 
is charged, consist of peroxide of lead, and 
constitute the active material of the cell. 
The negative grids have apertures filled 
with square buttons, which when in the 
charged condition are filled with porous 



STORAGE BATTERIES. 



355 





FIG. 119. SMALL STORAGE CELL. 



356 ELECTRIC INCANDESCENT LIGHTING. 

lead. In the cell shown, the plates are 
three inches square, and the weight of the 
entire cell, filled with solution, is four 
pounds. The capacity of this cell is about 
6 ampere-hours when discharged at normal 
rates. 

In a fully charged storage cell, the ma- 
terials filling the apertures in the grids are 
dissimilar ; namely, peroxide of lead and 
metallic lead. During discharge chemical 
actions occur, which result in reducing 
these substances to the same substance ; 
namely, monoxide of lead. When now 
the charging current is sent through the 
exhausted cell, a dissimilarity is again 
produced, the monoxide being converted to 
peroxide of lead on the positive plate, and 
into porous lead on the negative plate. It 
is evident, therefore, that it is not electric- 
ity which is stored, but energy in the form 



STORAGE BATTERIES. 357 

of chemical energy, and in a form capable, 
on discharge, of being released under suit- 
able conditions as electric energy. 

Fig. 120, shows a larger size of the same 
type of storage cell. Here five positive 
plates are associated alternately with six 
negative plates, so that both external plates 
are negative ; these plates are provided 
with rectangular apertures. The plates 
are bound together by an insulating frame 
F, F, F, and are individually separated or 
maintained at the proper distance apart- by 
sheets of asbestos. In the cell shown, the 
plates are 10.5" square, and the entire cell, 
with solution, weighs 170 pounds. Its 
normal capacity is 500 ampere-hours, or, 
approximately, 3 ampere-hours per pound 
of total weight. All the positive plates 
are connected together to form a single 
positive plate with terminal P, and all the 



358 ELECTKIC INCANDESCENT LIGHTING. 




FIG. 120. STORAGE CELL. 



STORAGE BATTERIES. 



359 



negatives are similarly connected to form 
a single negative terminal N. 

When storage cells are employed in large 
central stations for the supply of powerful 




FIG. 121. LARGE STORAGE CELL. 

currents, it is customary to associate large 
plates in single cells, rather than to employ 
a number of smaller cells in parallel. Fig. 



360 ELECTRIC INCANDESCENT LIGHTING. 

121, represents a form of large cell for such 
an apparatus. Instead of employ ing a glass 
jar, the containing vessel is of wood, with 
an interior leaden lining. Here 21 nega- 
tive plates are associated with 20 positive 
plates, each plate is 15.5" square, and the 
total weight of the cell, when filled with 
solution, is 800 pounds. The normal 
capacity of this cell is 5,000 ampere-hours, 
or about 6.4 ampere-hours per pound of 
total weight. 

It is evident that the storage capacity 
increases with the weight of the cells ; 
being over 6 ampere-hours per pound, 
with larsre cells, and with the smallest cells 

O 7 

about 1 1/2 ampere-hours per pound of 
total weight. The E. M. F. produced by 
the average storage cell is about 2 volts. 
When fully charged, while discharging, it 
is about 2.2 volts, and falls during dis- 




charge 

energy wcia^ ex- 

pressed in watt-hours is, therefore, approx- 
imately, 2 multiplied by the capacity of 
the cell in ampere-hours. Thus the cell 
last mentioned has an energy storage 
capacity of 2 X 5,000 = 10,000 watt- 
hours, or 10 KW-hours, under normal 
circumstances. 

Since incandescent electric lamps gener- 
ally require a pressure of about 115 volts, 
and since a single storage cell has only 2 
volts E. M. R, it is necessary to couple at 
least 57 cells in series, and, in order to al- 
low for drop of pressure in the feeders, 
mains and house wires, the usual number 
required for this purpose is from 60 to 65 
cells. For three-wire installations, twice 
this number is necessary, or about 120 
cells. Such a three-wire storage battery 



STORAGE BATTERIES. 363 

installation is represented in Fig. 122. 
The cells are arranged in series, the posi- 
tive terminal of one cell being connected to 
the negative terminal of the next. Each 
cell has 11 plates, 5 positive and 6 nega- 
tive, and the normal capacity of the cell is 
1,000 ampere-hours, giving a 10-hour dis- 
charge at the rate of 100 amperes. 

A storage battery plant requires for its 
convenient operation a switchboard with its 
accessories, such, for example, as is shown 
in Fig. 123. S, &, are two double-pole 
switches, one for controlling the charging, 
and the other the discharging circuit. The 
charging here being performed, as is usual 
in such cases, by a dynamo whose pressure 
is controlled by the field rheostat operated 
by a handle at F. A, A, are ammeters in 
the charging and discharging circuits ; V, is 
a voltmeter which by means of ihepressure 



364 ELECTRIC INCANDESCENT LIGHTING. 








B 



e> 





# 

FIG. 123. STORAGE BATTERY SWITCHBOARD. 

gwitch P, can be connected either to the 
dynamo terminals, or to the battery termi- 
nals, to show the pressure before the switch 
is thrown. T, is an automatic cut-out which 



STORAGE BATTERIES. 365 

disconnects the charging circuit of the 
dynamo, as soon as the C. E. M. F. of 
the cells exceeds the E. M. F. of the dynamo, 
and 0, is an overload switch in the dis- 
charging circuit, arranged automatically to 
break the circuit of the battery should the 
discharge become excessive. It, is a switch 
which may either be used to throw in and 
out reserve cells, in order to maintain the 
discharging pressure constant, or to throw 
in and oqt C. E. M. F. cells, that are 
employed in place of the rheostat in the 
lamp circuit during charge. 

The overload switch is shown in greater 
detail in Fig. 124. Here a coil of heavy 
wire (7, pivoted upon its axis, has its 
ends dipping in mercury cups. The coil 
is placed in the main circuit of discharge 
in such a manner that when the discharg- 
ing current becomes excessive, the electro- 



366 ELECTRIC INCANDESCENT LIGHTING. 

magnetic force developed by the coil rotates 
tlie helix and lifts the contact points P, P, 




FIG. 124. OVERLOAD SWITCH. 

out of the mercury cups. H, is the handle 
for restoring the circuit when desired. 

Fig. 125, shows & form of overload switch 
suited for heavier currents. The spring 
jaws, J, J, are in contact with the plates 
7J T, when the switch is closed, and the 
discharging circuit established. S, S 9 are 



STORAGE BATTERIES. 




FIG. 125. OVERLOAD SWITCH, CLOSED. 

spiral springs which tend to disengage the 
plates and open the switch, but whose ac- 
tion is prevented by the armature J., which 



368 ELECTRIC INCANDESCENT LIGHTING. 

normally holds the switch plates in posi- 
tion. The coil C, of heavy conductor, is 
placed in the discharging circuit, and, as 
soon as the current strength exceeds a cer- 
tain safe limit, it attracts the armature A, 
to the iron pofe piece P, thus allowing the 
springs &, S to act, and the plates T, T, to 
be thrown out of the jaws J, J, as shown 
in Fig. 126. 

In order to maintain a storage battery 
in proper working order, it is necessary to 
test the individual cells from time to time, 
for E. M. F. This is readily effected in 
practice, by means of any suitable voltmeter 
connected with electrodes for application 
to each separate cell. A convenient form 
of apparatus for this purpose is shown in 
Fig. 127. A simpler form of testing ap- 
paratus, not so accurate as the preceding, 
is shown in Fig. 128. It consists of a pair 



STORAGE BATTERIES. 




FIG. 126. OVERLOAD SWITCH, 
RELEASED. 



370 ELECTRIC INCANDESCENT LIGHTING. 

of handles with sharp metallic points, to 
make connection with the leaden electrodes 
of the cells, and connected by a loop of 



FIG. 127. STORAGE CELL VOLTMETER AND ELECTRODES. 

wire. In the end of one of the handles is 
a lamp socket in which a low volt lamp 
is inserted. If the cell tested is in good 



STORAGE BATTERIES. 371 




FIG. 128. SIMPLE FORM OF STORAGE CELL TESTER. 



372 ELECTRIC INCANDESCENT LIGHTING. 

order its E. M. F. will be sufficient to bring 
the lamp up to candle-power. 

The efficiency of a storage cell or battery 
is the ratio of the output to the intake. 
An ideally perfect battery would lose no 
energy, and would, therefore, have the 
same intake and output, representing an 
efficiency of unity, or one hundred per cent. 
In practice, the ampere-hour efficiency of a 
storage cell may be over ninety-five per 
cent, so far as regards electric quantity 
or ampere-hours, that is to say, if 100 
ampere-hours be supplied to a storage 
battery during charge, it may yield more 
than 95 ampere-hours during discharge. 
On the other hand, since the pressure at 
the terminals of a cell during charge is 
over 2 volts, rising toward full charge to 
2 1/2 volts, while the pressure during dis- 
charge is from 2.2 to 1.8 volts, the energy 



STORAGE BATTERIES. 373 

efficiency, as reckoned from the watt-hour 
output, is considerably less, and usually 
varies from seventy-five to eighty -five per 
cent, according to the conditions of the 
charge and discharge. A battery dis- 
charged at a rapid rate will not have so 
high an efficiency, either in quantity or in 
energy, as if slowly discharged. In relation, 
therefore, to coal consumed, the efficiency of 
a storage battery is about eighty per cent., 
but in relation to ampere-hours the effi- 
ciency may be over ninety-five per cent. 



CHAPTER XVIII. 

SERIES INCANDESCENT LIGHTING. 

WE have have hitherto described mul- 
tiple-connected lamps ; or, in the case of 
the three- wire system, lamps in series-mul- 
tiple. It sometimes happens, that a dis- 
trict to be lighted is scattered and wide 
spread, so that scattered lamps have to 
be supplied at considerable distances from 
the central station. As we have already 
shown, under these circumstances a very 
great amount of copper would require to 
be employed in their multiple-distribution. 
In order to avoid this, a series distribu- 
tion is sometimes adopted. Here, as we 
have already described, a number of sep- 
arate lamps are connected in series in one 



374 



SEKIES INCANDESCENT LIGHTING. 375 

circuit. Since in such a system of distri- 
bution the extinguishment of a single lamp 
would open the entire circuit, a simple au- 
tomatic safety device is required, which 
will establish a short circuit about the 
faulty lamp, in case it breaks, thus pre- 
serving the continuity of the circuit. 

A system of series-distributed incan- 
descent lamps may be operated from a 
constant high-potential dynamo. Thus, a 
dynamo of 1,000 volts E. M. F. may operate 
a circuit of 30 incandescent lamps, each 
having a pressure of 33 1/3 volts, includ- 
ing drop in connecting wires. Several 
such 1,000- volt circuits may be arranged in 
parallel, thus producing a multiple-series 
system of distribution, as shown in Fig. 
129. 

Such a series-connected system is some- 



376 ELECTKIC INCANDESCENT LIGHTING. 

times used for incandescent lamps in street 
lighting. It is not suitable for house 
lighting, since it is essential that the num- 
ber of lamps in each series circuit should 




a b c d 
129. MULTIPLE-SERIES SYSTEM. 

be as nearly constant as possible, and this 
precludes the possibility of cutting lamps 
out of a circuit when no longer required. 

Various forms of automatic circuit-pro- 
tecting devices have been produced. One 
of the simplest of these, called the film 
cut-out, consists of a thin strip of paper 
placed between two spring contacts con- 



SERIES INCANDESCENT LIGHTING. 377 

nected with two terminals of each lamp. 
While the lamp remains lighted, the elec- 
tric pressure across the thickness of the 
strip of paper is only a few volts ; i. e., the 
pressure at the lamp terminals, but if the 
filament should break, the pressure at the 
terminals is the full pressure of the circuit 
which may be 1,000 volts. This pressure 
is capable of piercing the thin paper sheet, 
thus establishing an arc, which instantly 
welds the two metal strips together, thus 
short-circuiting the lamp and re-establish- 
ing the circuit. 

As already stated, series incandescent 
lamps are generally employed for out-door 
lighting and, therefore, have to be pro- 
tected from the weather. The compara- 
tively high electric pressure employed on 
these circuits, not being safe to handle 
under all conditions, requires certain pre- 



378 ELECTRIC INCANDESCENT LIGHTING. 

cautions in insulation when introduced 
into buildings. Fig. 130, shows a form of 
lamp and fixtures suitable for out-door 
series-incandescent lighting. The lamp Z, 




FIG. 130. STREET FIXTURE, WITH SERIES INCANDESCENT 
LAMP. 

is placed in its socket beneath tne porce- 
lain deflector D, which not only serves to 
scatter and reflect the light, but also, in 
conjunction with the cover (7, to protect the 



SERIES INCANDESCENT LIGHTING. 379 

lamp socket from rain. The circuit wires 
Cj c, are brought to the socket of the lamp 
after being secured to the insulators I, I. 
Fig. 131, shows the same fixture with the 




FIG. 131. STREET FIXTURE, WITH LAMP REMOVED AND 
SOCKET EXPOSED. 

deflector D, removed, showing the socket 
>9, placed in the interior. Fig. 132 shows 
a form of lamp post suitable for street 
lighting with such lamps. Another form 



380 ELECTKIC INCANDESCENT LIGHTING. 




FIG. 132. LAMP POST. 



SERIES INCANDESCENT LIGHTING. 381 

of fixtures is shown in Fig. 133; here the 
incandescent lamp is provided with an 
external globe. 

Where a series circuit has already been 
installed for operating arc lamps, it is 




FIG. 133. STREET LAMP FIXTURE. 

sometimes desirable to insert incandescent 
lamps in the same circuit. This is done 
by employing series incandescent lamps of 
special manufacture. Since the current 
strength, in a series-arc circuit, is usually 



382 ELECTRIC INCANDESCENT LIGHTING. 

about 10 amperes, and is the same in all 
parts of the circuit, it is necessary that the 
incandescent lamps be made for this cur- 
rent strength. A fifty-watt 16-candle 
power lamp, taking 10 amperes, must be a 
5-volt lamp, since 5 volts X 10 amperes = 
50 watts. Consequently, the resistance 
of the lamp must be only 1/2 ohm, since 10 
amperes X 1 /2 ohm = 5 volts, and the 
filament must be comparatively short and 
thick in order to possess this relatively 
low resistance. It is evident that lamps 
of different candle power can be obtained 
from the use of such series circuits, by 
suitably adjusting the resistance of their 
filaments. The connections for such a 
series arc and incandescent circuit are 
shown in Fig. 134. 

Since series-arc circuits frequently em- 
ploy dangerously high pressures, it be- 



SERIES INCANDESCENT LIGHTING. 383 

comes unsafe to come in contact with the 
conductors of such circuits when standing 
on wet ground ; for, such circuits com- 




FIG. 134. SERIES ARC AND INCANDESCENT CIRCUIT. 

moiily have marked leakage and thus a 
dangerously high current might be sent 
through the body. Consequently, it is 



384 ELECTRIC INCANDESCENT LIGHTING. 

necessary carefully to insulate the keys 
and connections of incandescent lamps 
operated on arc circuits. 




FIG. 135. LAMP FOR SERIES-ARC CIRCUIT, WITH 
CUT-OUT SWITCH. 



SERIES INCANDESCENT LIGHTING. 885 

Fig. 135, shows a form of lamp suit- 
able for series-arc circuits. Like all 
series-connected lamps, it contains an au- 
tomatic cut-out, and of the film type al- 
ready described. It has no key, but is 
provided with a ceiling switch whereby 
it may be short-circuited and thus extin- 
guished. 



CHAPTER XIX. 

ALTERNATING-CURRENT CIRCUIT INCAN- 
DESCENT LIGHTING. 

SINCE incandescent lamps are frequently 
operated on alternating-current circuits, it 
may be well briefly to discuss some of tlie 
characteristics of these currents and in- 
stances of their commercial application. 

In a continuous current the direction of 
electric flow does not change. Its strength 
may vary periodically, in which case the 
current is said to pulsate; or, it may be 
unvarying, in which case the current is 
said to be steady. An alternating current, 
on the contrary, changes direction many 



NATING-CUKKENT OIROU 




times in a^s^jtrftfJ, f%ep$ being first' a wave 
or flow of curreStHlrro^^r'tEe circuit in 
one direction, and then a wave or flow 
of current in the opposite direction, and 
so on. Each of these waves or flows is 
called an alternation, and a complete to- 
and-fro motion, or double wave, is called 
a cycle. The frequency of alternation is 
the number of alternations or of cycles 
executed in a second ; thus ordinary com- 
mercial alternating circuits have a fre- 
quency of from 25 cycles, or 50 alternations 
per second, to 140 cycles, or 280 alterna- 
tions per second. The number of cycles, 
or complete periods, is sometimes symbol- 
ized by the sign ~, so that a frequency of 
140 complete periods, or cycles, per second 
would be written 140 ~. 

Between each pair of successive waves, 
at the time when the current is chang- 



388 ELECTKIC INCANDESCENT LIGHTING. 

ing direction, there is no current flowing 
in the circuit. Consequently, it might be 
supposed, when an alternating current, 
of say 120 ~, is sent through a lamp, since 
there would be 240 moments in each 
second when no current is flowing, that 
the light furnished by the lamp would 
pulsate, being extinguished and relighted 
240 times in a second. In point of fact, 
this tendency to pulsate does exist; but 
when the frequency is sufficiently high, 
before the filament loses enough of its heat 
to cease glowing, it receives a fresh acces- 
sion of heat from the succeeding wave 
of current. Moreover, the retina of the 
eye tends to retain its luminous impres- 
sions for a sufficiently great fraction of a 
second to aid in the apparent uniformity 
of the light. The result is, when the fre- 
quency is above say 30 ~, or 60 alterna- 
tions per second, i. e., 3,600 alternations 



ALTERNATING-CURRENT CIRCUIT. 389 

per minute, that the light of an incandes- 
cent lamp is practically steady. As the 
frequency is reduced, the higher economy 
lamps ; i. e., those which have a greater 
efficiency, or a greater number of candles- 
per-watt, are the first to suffer in apparent 
steadiness. First, because they are more 
brilliant for the same candle-power, or are 
operated at a high temperature, and the 
eye is much more sensitive to changes 
of brilliancy than to changes of candle- 
power, or, in other words, to changes in 
candle-power per square inch of bright 
surface, than to total candle-power; and 
second, because such lamps have usually 
thinner filaments, and hence chill more 
rapidly. 

The frequency employed in alternating- 
current circuits varies between 25 ~ and 
140 ~ per second. 



390 ELECTRIC INCANDESCENT LIGHTING. 

If an incandescent lamp be supplied by 
a continuous pressure, of say 110 volts, 
and gives a candle-power of 16 candles at 
this pressure, then if it be removed and 
connected with an alternating-current pres- 
sure of 110 volts, it will shine with equal 
brightness and give 16 candles as before, 
no matter what the frequency, provided 
only that the frequency be sufficiently 
great to keep the lamp from flickering. 
Similarly, the current strength, which the 
lamp will take, on an alternating current 
circuit, is the same as that which it takes 
on a continuous-current circuit. This is 
for the reason that although the strength 
of an alternating current is constantly 
fluctuating, between the apex of the suc- 
cessive waves and zero at the moments of 
reversal, yet the current is defined or 
measured by its heating effect, so that if 
half an ampere of continuous current 



ALTERNATING-CURRENT CIRCUIT. 391 

brings a given lamp to candle-power, then 
the alternating-current strength which also 
brings the lamp to candle-power, will be 
half an ampere, no matter what the outline 
of the current wave may be. Thus, it 
would be possible for each wave to have a 
current strength of 2 amperes at the apex, 
and yet to produce only the average heat 
effect of a half an ampere. Such a current 
would have an effective current strength 
of 1/2 ampere. In general, the maximum 
current strength is about forty per cent, in 
excess of the effective current strength, so 
that when an alternating-current ammeter 
shows that a current of one effective 
ampere is passing in a circuit, the apex of 
the successive current waves will, probably, 

attain a strength of 1 amperes. In 

the same way, if the pressure in an alter- 
nating-current circuit, as shown by lamps 



392 ELECTRIC INCANDESCENT LIGHTING. 

or by instruments, be 100 volts, the instan- 
taneous maximum value in the successive 
cycles will, probably, be about 140 volts. 

It is evident, therefore, that it would 
be possible to employ alternating-current 
generators instead of continuous-current 
generators, in a central station, for the dis- 
tribution of electric light. The drop of 
pressure, however, in the supply feeders 
and mains, would, in such a case, for reasons 
that it is not necessary here to consider, be 
greater than with the same strength of 
continuous current, and it is generally con- 
sidered, that it is disad vantageous to supply 
low-tension systems of incandescent light- 
ing from alternating-current generators. 
When, however, the lighting has to be dis- 
tributed at great distances, and, therefore, 
at a high electric pressure, in order to avoid 
expense in conductors, the alternating-cur- 



ALTERNATING-CURRENT CIRCUIT. 393 

rent system possesses decided advantages, 
since it readily lends itself to transforma- 
tion of pressure; that is to say, it is easy 
to take an alternating-current generator of 
say 2,000 volts E. M. F., and to transmit 
this pressure to considerable distances over 
comparatively small conductors, and then 
to reduce the pressure locally, within the 
precincts of buildings, to say 100 volts, by 
means of an apparatus, called an alternat- 
ing-current transformer. 

A form of alternating-current trans- 
former is shown in Fig. 136. Such an 
apparatus consists essentially of two coils 
of insulated wire, wound around a common 
laminated iron core. These coils are con- 
nected respectively with a high-pressure 
and a low-pressure circuit. In this case, 
the high-pressure circuit is the source of 
energy, or i\\z primary circuit, and the low- 



394 ELECTRIC INCANDESCENT LIGHTING. 

pressure circuit is the circuit of delivery, or 
the secondary circuit. The effect of send- 
ing an alternating current through the 
primary coil is to induce alternations of 




L,. . ^_ 



FIG. 136. ALTERNATING-CURRENT TRANSFORMER. 
CAPACITY 1 KW, OR 20 50- WATT LAMPS. 

the same frequency, but different E. M. R, 
in the secondary coil. If the secondary 
coil contains more turns than the primary, 
then the secondary E. M. F. is the greater. 
If, on the contrary, as in this case, the 



ALTERNATING-CURRENT CIRCUIT. 395 

secondary turns are fewer, then the second- 
ary E. M. F. will be lower. Transformers 
are, therefore, of two kinds ; namely, step-up 
transformers, or those which raise the pres- 
sure, and step-down transformers, or those 
which lower it. 

Like all machines for effecting the trans- 
formation of energy, alternating-current 
transformers waste some portion of what 
they receive. In large transformers this 
loss at full load is relatively very small, only 
about two per cent., so that the efficiency 
of a large transformer, at full load, is 
approximately ninety-eight per cent. On 
the other hand, the relative loss at very light 
load is necessarily much greater. During 
the day time, when comparatively few 
lamps are lighted over the distribution 
system, the power supplied to magnetize 
the transformers may be considerably 



396 ELECTRIC INCANDESCENT LIGHTING. 

greater than the power usefully expended. 
This is the only objection to the action 
of alternating-current transformers, and is 
outweighed when the distance to which 
the current has to be carried is sufficiently 
great, since, otherwise, a large amount of 
copper would have to be employed to 
transmit the necessary energy in any other 
way. A continuous current cannot be 
transformed without the aid of rotating 
mechanism. 

In Fig. 136, P, P, are the primary wires 
leading to the high-pressure mains, which 
are usually supported on poles overhead. 
S, 8, are the secondary wires leading to the 
interior of the building and acting as ser- 
vice wires. The apparatus represented in 
the figure has a capacity of 1 KW, and, 
therefore, is capable of supplying about 
20 fifty-watt incandescent lamps. If the 



ALTERNATING-CURRENT CIRCUIT. 397 

secondary pressure be 100 volts, the cur- 
rent strength at full load would be 10 am- 
peres approximately, since 100 volts X 10 
amperes = 1,000 watts. In the primary 
circuit the current strength will be about 
1 ampere at full load, if the primary 
pressure be 1,000 volts, since 1,000 volts 
X 1 ampere = 1,000 watts. In reality, 
owing to some loss of power in the trans- 
former, say 50 watts, the current strength 
would be somewhat in excess of 1 ampere. 
Moreover, in alternating-current circuits, 
the current strength is in excess of the 
number of amperes which, multiplied by 
the pressure in volts, gives the actual 
activity in watts. 

Transformers of small size, weight and 
capacity, are more expensive per KW, or 
per lamp, both to purchase and to operate 
than large transformers, since they require 



398 ELECTRIC INCANDESCENT LIGHTING. 

relatively more labor and material and have 
a lower efficiency. It is customary, there- 
fore, when possible, to supply several sets of 
secondary conductors, say in several adjacent 
buildings from a single large transformer, 
rather than have a transformer for each 
house. For the same reason, where single 
lamps have to be supplied by alternating 
currents at considerable distances apart, as, r 
for example, in street lighting, instead of 

employing a small ^th KW transformer 

for each lamp, the method is adopted of 
connecting a number of lamps in series, 
as in an arc circuit, and shunting each lamp 
by a coil called a reactive coil. This reac- 
tive coil allows almost the entire current 
strength in the circuit to pass through the 
lamp and takes only a small portion 
through its own circuit. If, however, the 
lamp filament breaks, thus interrupting the 



ALTERNATING-CURRENT CIRCUIT. 399 

circuit of that lamp, the reactive coil per- 
mits the full current strength to pass 
through it with only a comparatively small 
drop in pressure; namely, the pressure 




FIG. 137. SERIES-CONNECTED STREET LAMP FOR ALTER 
NATING-CURRENT CIRCUITS. 

equal to that of the lamp which has be- 
come extinguished. This drop is due to a 
C. E. M. F. established by the current in 
the circuit in passing through the reactive 
coil. Such a series lamp shunted by its 
reactive coil is represented in Fig. 137. 



400 ELECTRIC INCANDESCENT LIGHTING. 

The alternating currents required for 
alternating-current incandescent lighting, 




FIG. 138. ALTERNATING-CURRENT GENERATOR. 

are obtained from a form of dynamo known 
as an alternator. This dynamo does not 



ALTERNATING-CURRENT CIRCUIT. 401 

differ in principle from an ordinary con- 
tinuous-current generator, except that it 
does not commute the current in its line 
circuit. Fig. 138, shows a form of alter- 
nator having fourteen poles. Since the 
fourteen field magnet coils require to be 
supplied by continuous currents, the ma- 
chine is accompanied by a small continu- 
ous-current generator, called an exciter. 

Incandescent lamps, intended for alter- 
nating-current circuits, possess no peculiar- 
ity, that is to say, a lamp may be used 
indifferently on a continuous or on an alter- 
nating-current circuit, when the working 
pressures in each case, and the sockets, are 
the same. 



CHAPTEK XX. 

MISCELLANEOUS APPLICATIONS OF INCANDES- 
CENT LAMPS. 

BESIDES the various uses for the incan- 
descent lamp, which we have described, 
there are many others which want of space 
will prevent our discussing, except very 
briefly. 

The fact that the incandescent lamp is 
capable, within reasonable limits, of being 
made of almost any size, and the additional 
fact that the glowing filament is entirely 
protected by a surrounding glass chamber, 
permits the incandescent lamp to be 
employed for purposes in which other 
artificial illuminants would be impossible.. 



MISCELLANEOUS APPLICATIONS. 403 

We may mention, as one of such purposes, 
the employment of small suitably shaped 
incandescent electric lamps for exploring 
the cavities of the body. Incandescent 
lamps are thus employed by physicians 
and surgeons. For this purpose a small 
lamp, shaped so as to permit of its ready 
introduction into the cavity to be exam- 
ined, is mounted at the extremity of a 
suitable support. In some cases the ex- 
ploring lamp is sometimes placed in a 
sheath or tube, through the interior of 
which the illumined area is directly ob- 
served. 

An entirely distinct method, however, 
from the preceding is sometimes adopted ; 
namely, the method of trans-illumination. 
Here an attempt is made to illumine the in- 
terior cavity so as to permit it to be visible 
through the body as a translucent screen. 



404 ELECTRIC INCANDESCENT LIGHTING. 

The amount of light required to attain 
this result, is so great as to necessitate the 
liberation of considerable heat activity, and 
means have usually to be provided for 
keeping the lamp cool. This is done by a 




FIG. 139. MINIATURE INCANDESCENT LAMPS. 

jacket, in the exterior glass globe, through 
which cold water is kept circulating. 

Examples of three small lamps employed 
for surgical and dental purposes are seen 
in Fig. 139. Such lamps are generally 
called battery lamps, because they are cap- 



MISCELLANEOUS APPLICATIONS. 



405 



able of being operated from a primary 
or secondary battery. The usual voltage 
is from three to six volts. The efficiency 
of such lamps, in candle-power per watt, is 






3-Candle Lamp. 4-Candle Lamp. 6-Candle Lamp. 

FIG. 140. MINIATURE INCANDESCENT LAMPS. 

much less than that of larger lamps, owing 
principally to the rapid conduction of heat 
from the short filament through the con- 
ducting wires. Other forms of battery 
lamps, of candle-power as marked, are re- 
presented in Fig. 140. 



406 ELECTRIC INCANDESCENT LIGHTING. 

Sometimes in medical or surgical ex- 
aminations, a small incandescent lamp is 
mounted before a concave reflector, strapped 




FIG. 141. INCANDESCENT LAMPS, WITH REFLECTOR AND 

CONDENSING LENS. 

to the head of the observer. In other cases 
the lamp and reflector are mounted as 
shown in Fig. 141, within a tube mounted 



MISCELLANEOUS APPLICATIONS. 407 

on a suitable stand and provided with a 
condensing lens. 

Another use for the incandescent elec- 
tric lamp which is due to the fact that the 
glowing filament is hermetically sealed, is 
the use of safety incandescent lamps in 
mines, where the presence of fire-damp is 
feared. This form of safety lamp is in- 
tended to replace the Davy safety lamp. 
Such lamps are supplied by either a pri- 
mary or secondary battery placed in the 
lamp case. A form of such lamp is shown 
in Fig. 142. 

Battery or miniature incandescent lamps 
are also often employed for use with the 
microscope in the illumination of the 
object, since they are capable of being 
placed conveniently for observation. Va- 
rious designs of supports and reflectors are 



408 ELECTRIC INCANDESCENT LIGHTING. 

employed in connection with lamps for 
this purpose. 

The incandescent lamp is used exten- 




FIG. 142. SAFETY LAMP FOR MINES. 

sively on the modern steamship not only 
for purposes of general illumination of the 
vessel, but also for the lighting of the 




409 

stern-lights 
case of such 
lights, it is a matter of considerable im- 
portance that the continuity of service of 
the lamps be ensured, since the rupture 
of the filament might jeopardize the vessel. 
In order to lessen the liability of disabling 
the side-light, it is common to employ a 
double-filament lamp, sometimes called a 
twhi-filament lamp, so arranged that if one 
filament should fail, the other may con- 
tinue burning. At other times two sep- 
arate lamps are employed for the same 
purpose. A double-filament lamp is shown 
in Fig. 143. 

Incandescent lamps on board ship are 
operated at pressures between 100 and 120 
volts, almost invariably on the two-wire 
system. In warships, the pressure is usu- 
ally 80 volts, in order to facilitate the use 



410 ELECTRIC INCANDESCENT LIGHTING. 




FIG. 143. DOUBLE FILAMENT LAMP FOR SHIP'S 
SIDE-LIGHT. 



MISCELLANEOUS APPLICATIONS. 411 

of arc-light projectors without the addition 
of much resistance in the projector circuits. 

In the early history of ship lighting, the 
method was adopted of employing the 
ship's iron sheathing as a common return ; 
that is, one pole of all the lamps and also 
one pole of the dynamo being connected to 
the sheathing of the vessel, the other pole 
being connected to insulated conductors. 
This method was, however, found objec- 
tionable in practice and has been completely 
given up. Especial care has to be given 
to the insulation of wires and fixtures on 
board of ship. The connection boxes, 
switches, etc., are often arranged so as to 
be rendered completely water-tight. In 
Fig. 144, JTj is the switch handle, and H, 
the receptacle for the insertion of local 
connecting wires, leading to the lamp or 
other device to be operated. The cover 



4:12 ELECTRIC INCANDESCENT LIGHTING. 

C\ is intended to effect a water-tight seal 
when the receptacle is removed. In Fig. 




FIG. 144. WATER-TIGHT MARINE SWITCH 'AND RECEP- 
TACLE. 

145, the switch handle H, is recessed into 
the water-tistfit box in such a manner that 

O 

the cover 6 y , can enclose it in a water-tight 



MISCELLANEOUS APPLICATIONS. 413 

seal. The wires enter the box through the 
water-tight openings at O O. 

Miniature incandescent lamps are occa- 
sionally employed as a variety of electric 




FIG. 145. WATER-TIGHT MARINE SWITCH. 

jewelry, as in a scarf pin or ornament for 
the hair, such lamps being always operated 
from a small battery carried on the person. 
Similar lamps are also employed on the 



414 ELECTRIC INCANDESCENT LIGHTING. 

stage, for stage effects, being worn by the 
actors. 

Incandescent lamps are colored either 
by employing globes of tinted glass, or by 
dipping the clear lamp globes into a solu- 
tion of suitable dye. In the former case 
the coloring is permanent, in the latter 
case, it is temporary. 

Incandescent lamps, either plain or col- 
ored, are extensively employed in illumi- 
nated electric signs, where the lamps are 
grouped in the shapes of letters. Some- 
times, in order to attract attention to the 
sign, automatic switch devices are em- 
ployed, which at intervals extinguish some 
or all of the lamps ; or, blocks of lamps are 
arranged so as to be automatically cut out 
of circuit and cause letters to successively 
appear and disappear and words to be thus 
spelled out. 



416 ELECTRIC INCANDESCENT LIGHTING. 

The in -indescent electric liii'ht lends 

o 

itself very readily to decorative effect. 
This arises not only from the readiness 
with which the light is subdivided and 
distributed, but also from the fact that the 
glowing filament being protected by the 
surrounding glass chamber, permits the 
light to be partially buried in walls or 
ceilings, in a manner which would be im- 
possible with any other form of artificial 
illuminant. 

No description of decorative effect by 
incandescent lamps would be complete 
without some allusion to the magnificent 
spectacle that was afforded by the incan- 
descent lighting of the Court of Honor, at 
the World's Columbian Exhibition, at Chi- 
cago, in 1893. A faint conception only of 
the beauty of this scene may be gathered 
from the accompanying illustration in Fig. 



MISCELLANEOUS APPLICATIONS. 417 

146. The building in the background is 
the Administration Building, whose exte- 
rior is lighted by incandescent lamps. On 
the right hand side is the facade of Elec- 
tricity Building, and on the left hand is 
the facade of Machinery Hall. The entire 
bank of the waterway was illumined by 
incandescent lamps. 



INDEX. 



Actinic Effect of Light, 208. 
Activity, 62. 

and Candle-Power, Relation Between, 183. 

, Surface, of Incandescent Filament, 165. 

, Surface, of Positive Crater in Arc. 166, 

, Unit of, 63. 

Adapters for Lamps, 133, 134. 
Adjustable Lamp Pendant, 240. 
Age Coating of Lamp, 178. 
Air Pump, Mechanical, 125. 

Alternating-Current Circuit for Incandescent 
Lighting, 386 to 401. 

Current Generator, 400. 

Current Transformer, 393. 

Alternation, 386. 

, Frequency of, 387. 

Alternator, 400. 
Ammeters, 306. 

419 



420 t INDEX. 

Ampere, 56. 
Hours, 335. 

- Efficiency of Storage Cell, 372. 
Amyloid, Use of, for Filaments, 87, 
Analysis of Light of Glowing Filament, 74. 

- of Sunlight, 74. 

Antimonious Lead, Use of, in Storage Cells, 354. 

Arc, Voltaic, 18. 

Armature for Central-Station Generator, Winding 

of, 322, 323. 
of Central-Station Generator, 314. 

Artificial Illtiminants, Requisites for, C. 

Illumination, 1 to 17. 

Automatic Cut-Out for Storage-Battery Switch- 
board, 365. 

Safety Device for Incandescent Lamp, 375. 

Switch, 273. 

B 

Bamboo Filament, 107. 

- Filament, Preparation of, 86, 87. 
Bases, Lamp, 131, 132. 

Batteries, Storage, 345 to 373. 
Battery Incandescent Lamps, 407. 

-of Boilers, 311. 
, Voltaic, 47. 



INDEX. 421 

Begohrn, 247. 

Belt-Driven Generator, 327. 

Belting, 327. 

.Bipolar Generator for Isolated Plant, 330. 

Blackening of Lamp Chamber, 178. 

Block, Branch, 274, 275. 

Blowing of Fuse, 276. 

Boilers, Battery of, 311. 

Bougie-Decimate, 200. 

Boulyguine, 33. 

Boulyguine's Incandescent Lamp, 32, 33. 

Box, Carbonizing, 93. 

Boxes, Distribution, 280, 282. 

, Connecting, 263, 264. 

, Coupling, 295, 296. 

, Field Regulating, 306. 

, Junction, 300 to 303. 

Bracket, Lamp, 243. 

Lamp, Movable Arm for, 246. 
Branch, 274, 275. 

Coupling Boxes, 297. 

Cut-Out, 274. 

Branches, 251. 

Brass- Covered Conduit, 262. 

Brilliancy, 181. 

of Incandescent Filament, 168. 

British Candle, 199. 



422 INDEX. 

Brushes for Generator, 316. 
Bus Bars, Definition of, 223. 

c 

Candle Power and Activity, Relation Between, 

183. 
Power, Effect of Varying Pressure on, 188 

to 191. 

Power of Luminous Source, 199. 

Power, Mean Spherical, 207. 

Capacity, Energy of, Storage of Cell, 361. 

, Storage, 349. 

Carbon Filament, Life of, 16V. 

, Suitability of, for Incandescent Filament, 

83, 84. 
Carbonization, General Processes for, 84, 85. 

, Methods Employed for, 91 to 98. 

Carbonizing Box, 93. 

Frame, 94, 95. 

Cell, Charged, 352. 

, Counter-Electromotive Force of, 365. 

, Secondary, 352. 

Celluloid Filaments, 90. 

Central-Station Generator, Double Brushes for, 

316. 
Station Generators, 313. 



INDEX. 423 

Central Station, Load Diagram of, 347, 348. 

Station, Six-Pole Generator for, 317 to 320. 

Station Smashing Point of Lamp, 193. 

Station, Storage Cell for, 359. 

Station Switchboard, 305 to 308. 

Central Stations, 304 to 333. 

Charged Cell, 352. 

Charging Current, 352. 

Chlorine and Bromine, Residual Atmospheres of, 

in Lamp Chambers, 130. 
Circuit, Open, 46. 

, Primary, of Transformer, 393. 

, Secondary, of Transformer, 394. 

, Series Arc and Incandescent, 383. 

Circular-Mil, Definition of, 54. 
Circular-Mil-Foot, 54. 
Cleat Wiring, 254. 
Cleats, 255. 

, Wooden, 255. 

Coil, Reactive, 398. 
Cold Light, 10, 78, 79. 
Color, Cause of, 71, 72. 

Values, Day-Light, 72. 

Commutator of Central-Station Generator, 314. 

, Sparking at, 317. 

Concave Panel Shade and Reflector, 153. 
Concealed Work, 260. 



424 INDEX. 

Conduction of Heat, 75. 

Conductor, Neutral, of Three-Wire System, 222. 

, Twisted-Double, 248. 
Conductors, Double-Flexible, 249. 
, Drop in, 252. 

, Parallel, 248. 

, Silk-Covered, 248. 

, Solid, 247. 

, Supply, 250. 

, Twin, 248. 

, Stranded, 247. 

Conduit, Brass-Covered, 262. 

of Creosoted Wood, 288, 289. 

Conduits, 287. 

, Interior, 261, 262. 

Connecting Boxes, 263, 264. 

Connection Boxes for Interior Conduits, 264. 

in Series, 47. 

Consumers' Smashing Point of Lamp, 194. 
Continuous Electric Current, 304. 
Convection of Heat, 77. 
Cord, Flexible Lamp, 240. 
Corrugated Lamp Reflector and Shade, 155. 
Cotton Thread, Use of, for Filament, 87. 
Coulomb, 56. 
Coulomb-per-Second, 56. 
Counter-Electromotive Force Cells, 365. 



INDEX. 425 

Coupling Boxes, 295. 

Boxes, Branch, 297. 
Crater, Positive, of Arc, Surface Activity in, 

166. 

Creosoted Wood Conduit, 288, 289. 
Current, Continuous Electric, 304. 

, Electric, Pulsating, 386. 

, Steady Electric, 386. 

Strength, Effective, 391. 

Cut-Out, Branch, 274. 

Film for Incandescent Electric Lamp, 376, 

377. 

- Fixture, 278, 279. 

- Mains, 277. 

Switch for Series Circuit, 384. 

Cycle, 387. 

D 

Day-Light Color Values, 72. 
De Changy, 25. 

Incandescent Lamp, 26, 27. 

De Moleyn, 24. 

Diagram of Central-Station Load, 347, 348. 

Direct-Driven Generator, 328, 329. 

Distributing Point, 280. 

Distribution Boxes, 280, 283. 



426 INDEX. 

Distribution, Centers of, 253. 

, Series-Multiple Lamp, 221. 

, Three- Wire System of Lamps, 221 to 

224. 
Double Brushes for Central-Station Generator, 

316. 

Filament Lamps, 409. 

Flexible Conductors, 249. 

- Pole Switches, 267. 

Pole Switches, Forms of, 269, 270, 271. 
Drop in Conductors, 252. 
Dummy Moulding, 260. 
Dynamo-Electric Generator, 48. 
Dynamos or Generators, 311. 



E 

E. M. F., 44. 

Early History of Incandescent Lighting, 18 
to 42. 

Early Horse-Shoe Lamp, 104. 

Early Illuminants, 1 to 5. 

Incandescent Lamps, 19, 20. 

Effect of Temperature on Resistivity of Insula- 
tors, 55. 

Effective Current Strength, 391. 

Efficiency, Ampere-Hour, of Storage Cell, 372. 



INDEX. 427 

Efficiency of Incandescent Lamp, 170 to 233. 
' of Lamp, Effect of, on Duration of Life, 

184, 185. 

of Storage Cell, 372. 

of Transformers. 395. 

Electric Jewellery, 413. 

Lighting, Life Risks of, 14, 15. 

Pressure, 45. 

Quantity, Unit of, 56. 

Resistance, 49. 

Electrolier, 243. 

Electrolytic Meter, 335 to 339. 

Seal, 108. 

Electromotive Force, 43. 
Elementary Electrical Principles, 43 to 64. 
Elements or Plates of Storage Cell, 351. 
Emissivity of Incandescing Filament, 80, 81. 
of Lamp Filament, Effect of Surface on, 

180. 
Energy Efficiency of Storage Cell, 372, 373. 

Storage Capacity of Secondary Cell, 361. 

Storage of Cell, 361. 

Equalizer Switch, 235, 236. 
Ether, Luminiferous, 67. 

, Universal, 67. 

Evaporation of Incandescent Filament, 176, 177. 
Exciter, 401. 



428 INDEX. 

F 

Factor, Load, 349. 

Farmer, 36. 

Farmer's Incandescent Lamp, 35, 36. 

Feeder Distribution, 229. 

Distribution, Three- Wire System of, 231, 

232. 
Equalizer Resistance, 234. 

Load, Methods of Overcoming Inequali- 

ties of, 233, 236. 

Regulators, 233. 
- System, 253. 

Tubes, 298, 299. 

Feeders for Lamp Distribution, 228. 

Feeding Point, 298. 

Field Magnet Coils of Generator, 314. 

Regulating Boxes, 306. 

Filament, Bamboo, Preparation of, 86, 87. 

, Effect of Flashing on Emissivity of, 116, 
117. 

, Effect of Surface on Emissivity of, 180. 

, Incandescing, Surface Activity of, 80, 81. 

, Mounting of, 99, 100, 
, Sealing-in of, 118. 

, Shadows, 1/9. 

, Spotted, 112. 




Filaments, Amyloids, 

, Celluloid, 90. 

, Flashing Process 

, Methods Employed for 

91 to 98. 

, Squirted, 88, 89, 97. 

, Stopper-Mounted, 122, 123. 

, Use of Cotton Thread for, 87. 
Fire Fly, Radiation of, 78. 
Fittings, Lamp, 135 to 162. 

Five- and Four-Wire Systems of Lamp Distribu- 
tion, 225. 
Fixture Cut-Outs, 278, 279. 

Molding, 259. 

for Street Incandescent Lamp, 381, 382. 

Fixtures and Wiring for Houses, 237 to 283. 
Flashing Process for Filaments, 113, 114, 115. 
Flexible Lamp Cord, 240. 

Lamp Pendant, 239, 240. 
Flush Switches, 272. 
Foot-Pound, 59. 
Foot-Pound-per-Second, 63. 

Four- and Five-Wire Systems of Lamp Distribu- 
tion, 225, 

Frame, Carbonizing, 94, 95. 
French Standard Candle, 200. 
Frequency, Effect of, on Steadiness of Light, 388. 



430 INDEX. 

Frequency of Alternation, 387. 

, Luminous, 68. 

Full- Wire Guard for Incandescent Lamp, 158. 
Fuse, Blowing of, 276. 

, Cut-Out, 273. 

, Safety, 274. 

G 

Geissler Type of Mercury Pump, 127. 
Generator, Alternating-Current, 400 

, Dynamo-Electric, 48. 

, Field Magnet Coils of, 314. 

Unit, 308. 

Generators, Multipolar, 316. 

Generators or Dynamos, 313. 

Glass Lamp Shades, 156. 

Glow Worm and Fire Fly, Radiation of, 78. 

Glowing Filament, Analysis of Light Produced 

by, 74. 
Grids of Storage Cell, 351. 

H 

Half-Shade for Incandescent Lamp, 151. 
Half Wire-Guard for Incandescent Lamp, 157. 
Heat, Conduction of, 75. 
, Convection of, 77. 



INDEX. 431 



Heat, Molecular Transfer of, 76, 77. 

, Radiation of, 75. 

High-Economy Lamps, 389. 
Horizontal Intensity, Maximum, 207. 
Horse-Power, Definition of, 63. 
Hours, Ampere, 335. 

, Watt, 335. 

House Fixtures and Wiring, 237 to 283. 



Illuminants, Early, 1 to 5. 
Illuminated Electric Signs, 414. 
Illumination, Actual Values of, 206. 

, Artificial, 1 to 17. 

, Law of, 203, 204, 205. 

, Significance of, 198. 

, Unit of, 202. 

Incandescent Lamp, 163. 

Lamp, Automatic Safety Device for, 375. 

Lamp, Efficiency of, 170 to 233. 

- Lamp, Half Wire-Guard for, 157. 
Lamp, Multiple-Series Distribution of, 

376, 377. 
Lamp, Street Fixture for, 378. 

- Electric Lamp, Film Cut-Out for, 376, 377. 
Electric Lamp, Physics of, 65 to 82. 



432 INDEX. 

Incandescent Filament, Brilliancy of, 168. 
Filaments, Evaporation of, 176, 177. 

- Filament, Total Candle-Power of, 168, 169. 

- Filaments, Surface Activity of, 165. 
Lamp, Full Wire-Guard for, 158. 

- Head-Lights for Ships, 409. 
Lamps, Early, 19, 20. 

- Lamps, Miniature, 404, 405. 

Lamps, Miscellaneous Applications of, 

402 to 417. 

Lamp, Varying Candle-Powers of, 209. 

Lighting, Early History of, 18 to 42. 

Lighting, Fire Risks of, 13, 14. 
Lighting, Alternating-Current Circuit for 

386 to 401. 

Lighting, Decorative Effects in, 416, 417. 

Side-Lights for Ships, 409. 

Signal Lights for Ships, 409. 

Stern-Lights for Ships, 409. 

Filament, Emissivity of,-80, 81. 

Filament, Temperature of, 82, 174. 

Intake Wires, 280. 
Intensity, Luminous, 69. 

, Maximum Horizontal, 207. 

Interior Conduit Joints, 263. 

Conduit Junction Boxes, 264. 

Conduit, Junction Boxes for, 265. 



INDEX. 433 

Interior Conduits, 261, 262. 
Isolated Lighting Plants, 324 to 333. 

Plant, Smashing Point of Lamps, 194, 195. 

- Plants, 324 to 333. 
Plants, Quadripolar Generator for, 330, 332. 



Jewellery, Electric, 413. 

Joints of Filament with Leading-in- Wires, Bolt 

and Nut Type, 108. 
, Butt Joint Type, 111. 

, Socket Type, 108. 

, Interior Conduit, 263. 
Joule, 60. 

Joule-per-Second, 63. 
Junction Boxes, 300 to 303. 
Interior Conduit, 264. 

K 

Keyless Wall-Socket, 138. 
Key-Socket Push Button, 145. 

Wall-Socket, 139. 
Keys for Sockets, 140 to 142. . 
King, 27. 
Kosloff, 29. 
Konn, 29. 
Komi's Incandescent Lamp, 30, 31. 



434 INDEX. 



Lamp Adapter, 133. 

, Age-Coating of, 178. 

- Bases, 131, 132. 

- Bracket, 243. 

Chamber, Blackening of, 178. 

, Filament Shadows on, 179. 

, Machine Sealing of, 121. 
, Sealing Off of, 127, 128. 

, Steam-Tight, 161, 162. 

Cord, Flexible, 240. 



Cords, Silk, 248. 

Distribution, Series-Multiple System of, 221. 
, Distribution Systems of, 209 to 236. 

Filament, Relation Between Efficiency, 

Candle-Power, and Surface Activity of, 
180. 

Fittings, 135 to 162. 

Guard, Portable, 160. 
, Incandescent, 163. 

, Leading-in- Wires of, 100. 

, Mean Spherical Candle-Power of, 207. 

Pendant, Adjustable, 240. 
, Flexible, 239, 240. 

, Portable Incandescent, 238. 

Post for Incandescent Lamps, 380, 381. 



INDEX. 435 

Lamp Reflector and Shade, Corrugated, 155. 

Renewals, Rules for Best Commercial 

Results, 196, 197, 198. 

Shades, Glass, 156. 

Shadows, 149 to 156. 

, Smashing Point of, 192. 

, Semi-Incandescent, 37, 38, 39, 

Socket, Temporary, 147. 

Socket, Weather-Proof, 148. 

Sockets, 135 to 140. 

, Stopper, 121, 122, 123. 

Switch, 140. 

Switches, 267. 

, Twin-Filament, 409. 

Lamps, Battery-Incandescent, 407. 

, Connection in Parallel, 210. 

, Diagram of Multiple Connection of, 212. 

, Distribution of by Four- and Five-Wire 

Systems, 225. 

, Double-Filament, 409. 

, Incandescent, Use of, for Surgical Explo- 
ration, 403. 

, Miniature Incandescent, 404. 

, Safety Incandescent, 407. 

, Series Connected, Diagram of, 211. 

, Series Connections of, 210. 

, Spring Socket for, 146. 



436 INDEX. 

Lamps, Tree Distribution of, 230. 

Law of Illumination, 203. 

Leading-in Wires of Lamp, 100. 

Life of Filament, Circumstances Governing, 167. 

of Incandescent Filament, 167. 

- of Lamp and Efficiency, Relation Between, 

183. 

Light, Actinic Effect of, 208. 
, Monochromatic, 73. 

, Objective, Significance of, 66. 

, Significance of term, 198. 

, Subjective, Significance of term, 66. 

, Two-Fold Use of Word, 66. 

, Unit of Total Quantity of, 201. 
Lighting Plant, Isolated, 325. 

, Series Incandescent, 374 to 385. 

Load Diagram of Central Station, 347, 348. 

Factor, 348. 
Lodyguine, 28. 

Long Life vs. Low Efficiency, 185, 186. 
Lumen, 201. 
Luminiferous Ether, 67. 
Luminous Frequency, 68. 

Frequency, Effect of Temperature on, 

68, 69. 

Intensity, 69. 

Intensity, Standards of, 200. 



INDEX. 437 



Luminous Intensity, Unit of, 199. 

Source, Candle-Power of, 199. 
Lux, 202. 
Lux-Second, 208. 

M 

Machine Seal of Lamp Chamber, 121. 
Main Conductors, Overhead, 284. 

- Cut-Outs, 277. 

- Switch, 277. 
Tubes, 293. 



Mains, 250. 

, Street, 284 to 303. 

, Three- Wire, 276. 

, Two- Wire, 276. 
Man Holes, 287. 
Marine Switch for Lamps, 412. 
Maximum Horizontal Intensity, 207. 
Mean Spherical Candle-Power, 207. 
Mechanical Air Pump, 125. 
Mercury Pump, 125. 

Pump, Geissler Type, 127. 
Mercury Pump, Sprengel Type, 127. 
Metallic Half-Shade for Incandescent Lamp, 151, 

Lamp Shades, 149 to 153. 

Meter, Electrolytic, 335 to 339. 
Meters, Electric, 334, 344. 



438 INDEX. 

Methods for Overcoming Inequality of Feeder 
Loads, 233, 236. 

Mil-Foot, Circular, Definition of, 54. 

Miscellaneous Applications of Incandescent Lamps, 
402 to 417. 

Molecular Transfer of Heat, 76, 77. 

Monochromatic Light, 73. 

Molding, Dummy, 260. 

, Picture or Ornamental, 259. 

, Section of, 258. 

, Three- Wire, 257. 

Mounting of Filament, 99, 100. 

Movable Arm for Bracket Lamp, 246. 

Multiple and Series Systems of Lamp Distribution, 
Relative Advantages of, 212 to 220. 

Connected Lamps, Diagram of, 212. 

Series System of Distribution of Incan- 
descent Lamps, 376, 377. 

Multipolar Generators, 316. 

N 

Negative Plate of Storage Cell, 351. 

Pole, 44. 

Terminal, 44. 

Neutral Conductor of Three- Wire System, 222. 
Non-Luminous Heat, 10. 



INDEX. 439 

o 

Occluded Gas Process, 128, 129. 
Ohin, 57. 

, Definition of, 50. 

Ohm's Law, 57. 

Open-Circuit, 46. 

Ornamental Moulding, 259. 

Outlet Boxes, 266. 

Output Wires, 282. 

Overhead Main Conductors, 284. 

Wires, 284. 

Overload Switch for Storage Battery Switch- 
board, 366 to 370. 



Panel Reflectors, 153, 154. 

Parallel Conductors, 248. 

Parchmentizing Process, 85, 86. 

Pendant Lamp, 244. 

Petrie, 24. 

Phot, 208. 

Physics of the Incandescent Lamp, 65 to 82. 

Plant for Isolated Lighting, 325. 

Plants, Isolated, 324 to 333. 

Plates or Elements of Storage Cell, 351. 



440 INDEX. 

Platinum- Wire Incandescent Lamps, Requisites 
for, 21, 22. 

Wire, Use of, for Sealing-in Lamp Chamber, 

105. 

Plug, Cut-Outs, 277. 
Point, Distributing, 280. 

, Feeding, 298. 

Pole, Negative, 44. 

, Positive, 44. 

Portable Electric Incandescent Lamp, 238. 

Lamp Guard, 160. 
Positive Plate of Storage Cell, 351. 

- Pole, 44. 

Terminal, 44. 
Pressure, Electric, 45. 

, Unit of, 46. 

Switch for Storage Battery Switchboard, 

364. 

Wires, 298. 

Primary Circuit of Transformer, 393. 
Pulsating Electric Current, 386. 
Pump, Mercury, 125. 
Push-Button Key Socket, 145. 

Q 

Quadripolar Generator for Isolated Plants, 330, 332. 



INDEX. 441 

R 

Radiation of Glow- Worm and Fire-Fly, 78. 

- of Heat, 75. 
Rate-of- Doing- Work, 62. 
Radiation, Selective, 79. 
Rays, Ultra-Violet, 70. 
Reactive Coil, 398. 

Recording Wattmeter, 341 to 349. 
Reflector Shade for Incandescent Lamp, 152. 
Regulators, Feeder, 233. 
Requisites for Artificial Illuminants, 6. 
Residual Atmosphere, Lamp Chambers Inten- 
tionally Provided with, 130. 
Resistance, Electric, 49. 

- Electric, Unit of, 50. 

for Feeder Equalizer, 234. 

, Specific, 53. 

Resistivity, 53. 

of Conductors, Effect of Temperature on, 

55. 
of Insulators, Effect of Temperature on, 

55. 

Reynier, 38. 

Reynier's Semi-Incandescent Lamp, 38, 39. 
Reynier- Werdermann's Incandescent Lamp, 41, 42. 
Risers, 250. 



442 INDEX. 

s 

Safety Incandescent Lamps, 407. 
- Fuse, 274. 

Sawyer, 33. 

Sawyer's Incandescent Lamp, 34. 

Safety Device, Automatic, for Incandescent Lamp, 
375. 

Screw Cleats, 256. 

Seal, Machine, of Lamp Chamber, 121. 

Sealiug-in of Filament, 118. 

Sealing-off of Lamp Chamber, 127, 128. 

Secondary Cell, 352. 

Circuit of Transformer, 394. 

Selective Absorption of Light Radiations, 71, 72. 

Radiation, 79. 

Semi-Incandescent Lamp, 37, 38, 39. 

Series and Multiple Distribution, Relative Advan- 
tages of, 212 to 220. 

Arc and Incandescent Lamp Circuit, 383. 

Connected Lamps, Diagram of, 210. 

Connection, 47. 

Connections of Lamps, 210. 

Incandescent Lighting, 374 to 385. 

Multiple System of Lamp Distribution, 

221. 

Service Wires, 250. 



INDEX. 443 

Shades for Incandescent Lamps, 149 to 156. 

Shadows, Filament, 179. 

Ship Lighting by Incandescent Lamps, 412. 

Ships, Incandescent Head-Lights for, 409. 

, Incandescent Side-Lights for, 409. 

, Incandescent Stern-Lights for, 409. 

Short-Circuit, 272. 

Short Life vs. High Efficiency, 185, 186. 

Signal Lights for Ships, Incandescent, 409. 

Signs, Illuminated Electric, 414. 

Silk-Covered Conductors, 248. 

Lamp Cords, 248. 

Single-Pole Switch, Simple Form of, 268. 

Pole Switches, 267. 

Six-Pole Generator for Central Station, 217 to 
320. 

Smashing Point of Lamp, 192. 

Point of Lamp from Central Station Stand- 
point, 193. 

Point of Lamp from Consumers' Stand- 
point, 194. 

Point of Lamp from Isolated-Plant Stand- 
point, 194, 195. 

Socket Keys, 140 to 142. 

Sockets, Simple Form of, 137. 

Solid Conductors, 247. 

Wires, 246. 



444 INDEX. 

Sparking at Commutator, 317. 

Specific Resistance, 53. 

Spotted Filament, 112. 

Sprengel Type of Mercury Pump, 127. 

Spring Socket for Lamps, 146. 

Squirted Filaments, 88, 89, 97. 

Starr, 27. 

King Incandescent Lamp, 27, 28. 

Standard Candle, French, 200. 

of Luminous Intensity, 200. 

Storage Cell Tester, Simple Form of, 371, 372. 

Stations, Central, 304. 

Steadiness of Light, Effect of Frequency on, 388, 

Steady Electric Current, 386. 

Steam-Tight Lamp Chamber, 161, 162. 

Step-Down Transformer, 395. 

Step-Up Transformer, 395. 

Stern-Lights for Ships, Incandescent, 409. 

Stopper Lamp, 121, 122, 123. 

Stopper-Mounted Filaments, 122, 123. 

Storage-Battery Switchboard, 363 to 369. 

Batteries, 345 to 373. 

Capacity, 349. 

Cell, Efficiency of, 2, 372. 

- Cell, Energy Storage Capacity of, 361. 

Cell, for Central-Station Work, 359. 

Cell, Energy Efficiency of, 372, 373. 



INDEX. 445 

Storage Cell, Plates or Elements of, 351. 

Cell, Negative Plate of, 351. 
Cell, Positive Plate of, 351. 

Cell, Voltmeter and Electrodes, 370. 

Stranded Wires, 246. 

Conductors, 247. 

Street Incandescent Lamp Fixture, 381, 382. 

Fixture, for Series-Incandescent Lamp, 378. 

Lamps, Series Connected for Use on Alter- 
nating-Current Circuits, 399. 

Mains, 284 to 303. 

Sub Mains, 250. 

Subways, 285, 286. 

Sunlight, Analysis of, 74. 

Color Values of Artificial Illuminants, 8, 9, 

12. 

, Frequencies Present in, 70. 

Supply Conductors, 250. 

Surface Activity of Incandescing Filament, 80, 81, 
165. 

Activity of Lamp Filament, 180. 

Activity of Positive Crater of Arc, 166. 

Surgery, Use of Incandescent Lamps in, 403. 

Suspended Lamps, Wire Guards for, 159. 

Switch, Automatic, 273. 
, Flush, 272. 

for Lamps, 140. 



446 INDEX. 

Switch, Main, 277. 

, Marine, for Lamps, 412. 

, Pressure, for Storage-Battery Switch- 
board, 364. 

, Overload, for Storage-Battery Switch- 
board, 365, 366 to 370. 

Switchboard for Central Station, 305 to 308. 

Switches, Double-Pole, 267. 

for Lamps, 267. 

, Single-Pole, 267. 

System, Feeder, 253. 

, Three-Wire, of Lamp Distribution, 221 to 

224. 

Systems of Lamp Distribution, 210. 

T 

Taps, 251. 

Temperature, Effect of, on Luminous Frequencies, 

68, 69. 

, Effect of, on Resistivity of Insulators, 55. 

of Incandescing Filament, 82, 174. 

Temporary Lamp Socket, 147. 
Terminal, Negative, 44. 

, Positive, 44. 

Tester for Storage Cells, Simple Form of, 371, 

372. 



INDEX. 447 

Thermostat, 339. 

Three-Wire Mains, 276. 

Moulding, 257. 

System, Neutral Conductor of, 222. 

System of Feeder Distribution, 231, 232. 

System of Distribution, 221 to 224. 

Time Illumination, Unit of, 208. 

Total Candle-Power of Incandescent Filament, 
168, 169. 

Transformer, Alternating- Current, 393. 

, Primary Circuit of, 393. 

, Step-Up, 395. 

, Secondary Circuit of, 394. 

Transformers, Effect of Size and Weight on Cost 
and Efficiency of, 397, 398. 

Efficiency of, 395. 

Step-Down, 395. 

Trans-Illumination, 403. 

Tree Distribution of Lamps, 230. 

Twin Conductors, 248. 

Filament Lamp, 409. 

Twisted Double Conductor, 248. 

Two- and Three-Wire Systems of Lamp Distribu- 
tion, Relative Economy of, 223, 224. 

Two-Wire Mains, 276. 

Tube, Underground, 292. 

Tubes, Feeder, 298, 299. 



448 INDEX. 

u 

Ultra-Violet Rays, 70. 
Underground Tube, 292. 
Unit Generator, 308. 

of Activity, 63. 

of Electric Activity, 63. 

- of Electric Flow, 56. 

of Electric Power, 63. 

of Electric Pressure, 46. 

of Electric Quantity, 56. 

of Electric Resistance, 50. 
of Illumination, 202. 

of Illumination, Intensity of, 199. 

of Time Illumination, 208. 

of Total Quantity of Light, 201. 

of Work, 59. 
Universal Ether, 67. 

V 

Violle, 200. 
Volt, 46. 

Ampere, 63. 

Coulomb, 61. 

Coulomb-per-Second, 63. 

Voltaic Arc, 18. 
Battery, 47. 



INDEX. 449 

Voltmeters, 306. 

and Electrodes for Storage Cell, 370. 

w 

Wall Socket, Key, 139. 

Socket, Keyless, 138. 

Watt-Hours, 335. 

Wattmeter, Recording, 341 to 349. 

Weather-Proof Lamp Socket, 148. 

Werdermann, 40. 

Werdermann's Semi-Incandescent Lamp, 41. 

Wire-Guards for Suspended Lamps, 159. 

Wires, In -Take, 280. 

, Overhead, 284. 

, Pressure, 298. 

, Service, 250. 

, Solid, 246. 

, Stranded, 246. 
Wiring and Fixtures for Houses, 237 to 283. 

Cleat, 254. 

Wooden Cleats, 255. 
Work, 59. 

, Concealed, 260. 
, Unit of, 59. 




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