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July 1964 ARS - 33-94

United States Department of Agriculture
Agricultural Research Service

BASIC SEMICONDUCTOR CIRCUITRY FOR ECOLOGICAL AND

BEHAVIORAL STUDIES OF INSECTS

by Philip S. Callahan
Entomology Research Division

I have prepared this report primarily to answer queries entomologists
about electronic techniques I have used in my ecological studies of the corn
earworm, Heliothis zea (Boddie). In these studies, conducted for the most part
at the Southern Grain Insects Research Laboratory at Tifton, Ga., during 1962-
63, I utilized certain standard circuits, which I modified slightly. These
original circuit designs can be found in the publications on electronics marked
with an asterisk in the References Cited section on page 9 of this report.

This report includes descriptions of basic semiconductor circuitry for
accurate measurements of an insect's environment and behavior; some methods for
using Ohm's law to calculate resistance in meter-recording circuits; an expla-
nation of the characteristics of photoconductive and photovoltaic cells,
thermistors, and pressure-sensitive microducers; and a presentation of schematics
and examples of many simplified semiconductor circuits I have used to study the
environment and behavior of the corn earworm moth.

From the first discovery by Edmond Becquerel in 1839 of the photoemissive
effect, until after 1930 when the theoretical studies by Hertz, Elster, Geitel,
et al. had been accomplished, little practical use was made of the unusual
solid-state phenomena, most probably because of the small amount of electrical
current they generate or control. In the years since World War II, however, the
development of solid-state physics has progressed so rapidly, and semiconductors
are now employed in such a diversity of circuits, that it is almost impossible
to remain abreast of the field. New uses for control and recording mechanisms
are limited only by a person's imagination, and entomologists, once they become
acquainted with the subject, are apt to increase the list of uses indefinitely.

Recording

The circuits described here are for read-out on a microammeter or a micro-
ammeter-galvanometer recorder such as ,the small, inexpensive, 50- or 100-micro-
ampere Amprobe “ recorder (fig. 9d) yy There are over 200 manufacturers of

ay Mention of a proprietary product in this publication does not consti-
tute a guarantee or warranty of the product by the U.S. Department of Agricul-
ture, and does not imply its approval by the Department to the exclusion of
other products that may also be suitable.

various special-type recorders in all price ranges. The electrical characteris-
tics and working mechanisms of these recorders are listed in the extremely
useful Recorder Manual by Aronson (1962). The inexpensive Amprobe instrument is
a@ pressure-sensitive, paper type, with a lift-plate stylus, and with a 5-second
action and chart speeds up to 15 inches per hour. The 50-microampere model used
in these circuits has a 7400-ohm meter resistance.

Ohm's Law

Although the voltage and currents involved are of low value, it is important
to have a basic understanding of electrical resistance so that the meter mechanism
of the recorder will not be damaged when setting up the circuits. Ohm's law is
used to determine the value of the resistances in the meter circuit.

Ohm's law, in common terms, states that the current in amperes (I) is equal
to the pressure in volts (E) divided by the resistance (R) in ohms; that is:

l=

TO| ts

» or transposed,

ty

R= 7, or E =IR.

In a series circuit the total resistance is the same as the individual
resistance, i.e.,
Rn = Ry ae R, ate Ra et cetera.

Thus, using a 1.4-volt mercury battery, the current that would flow through
a microammeter recorder with a 7400-ohm resistance is:

fies ag
Te 7hOO ohms = 0.000189 amp.
6

Since 1 microampere (ua) = 1/1,000,000 of an ampere, then 0.000189 X 10° =

189 pa. As the maximum deflection of the meter is only 50 na, it is easily seen
that the recorder in series with a 1.4 battery would be damaged by drawing more
than three times its rated capacity.

If we insert a resistor (for example 30,0CO ohms) in series with the meter
resistance, we decrease the current across the meter coil (fig. 1A). We then
have a series curcuit where:

ae _ 1-4 V__ ft ~ 0.0000374 amp. x 10° oi Gua
T= 3B 3700 ome te eae

The current flowing in the circuit is thus 37.4 pa, or 12.6 ya below the maximum
allowable meter current of 50 na.

If resistors are connected in parallel, then the total resistance is less
than the lowest value of resistance in the parallel circuit. It is desirable to
shunt across the meter so that Ry (fig. 1B) may be used as a control resistor,
leaving the shunt to divert some of the excessive current from the meter. This,
in effect, makes a series-parallel circuit. R, is the series control resistor,
and Ro a 200-ohm shunt resistor; along with R32, the meter resistance forms the
parallel circuit.

ae ee

To determine the current across the parallel resistance, the equivalent
nesuisicance Or Ra + R3 is found by using the reciprocal of the reciprocals
formula where:

R = ae
eq
iL al
= + =
HD B3
Req = ak
al ny od
200 7400
Reta sa iL = als = 195 ohms.
6 = =—2 = SS SSE 2S
OROOSM OF O00 13 0'.005133

The parallel circuit Ro + R. has an equivalent resistance of 195 ohms, and

is now treated along with Rj as part Ova ySerilesicLrcuist),. SOmthat Rp = RL + R,

or Rp = 30,000 + 195 = 30,195 ohms. q

The total current is in =E = TL st or 0.0000464 amp. X 10° = 46.4 pa.

Rn 30195 ohms

To find the current in the meter (R3), which is a branch of the parallel

circuit, determine the voltage across the circuit from the equivalent IR drop;
then divide this voltage by the resistance of Bey the meter element.

I eR

Tel
E = 0.0000464 amp. X 195 ohms
E = 0.009 volts, then:

E =O COOMA ais
7400 ohms 7400 ohms

meter current I =

@.000012 amp. © 10° = 1.2 ne.

Thus, 1.2 pa will be the needle deflection on the recorder.
Semiconductors

A semiconductor may be described as a material with an electrical conduc-
tivity between that of a metal and an insulator; i.e., between extremely high
and almost no conductivity. .Its conductivity increases as the temperature
increases, whereas with a metal, the conductivity decreases as the temperature
increases. Each semiconductor described here may be thought of as a variable
resistor in which the resistance to flow of current changes with the correspond-
ing change of the physical environment; e.g., the increase or decrease of
light, temperature, or pressure, as described in this paper (figs. 7 and 8).
Humidity is not considered since a really efficient solid-state device depend-
ent on humidity has not yet been developed.

From the above definitions it is apparent that if a solid-state semiconductor
is substituted for control resistor Ry (fig. ID) then this substituted resistance
will vary the current flow in the meter or recorder according to its resistance
change, which is dependent on the environment. Rj, instead of being a 30,000-ohm,
manually operated, variable potentiometer, then becomes an environmentally operated
resistance. Usefulness of such environmentally controlled circuits to the insect
ecologists is multifold.

Solid-state, resistance-control mechanisms are classified according to the
environmental factor upon which they are dependent, and also according to physical
properties. They are here grouped into the following categories:

Photoconductive Cells.--Photoconductive cells are cells in which the electric-
al resistance varies inversely with the intensity of light that strikes the active
Substance. Many such cells are commercially available today. They are sometimes
called light-dependent resistors (LDR) and are usually made of thin layers of
selenium, silicon, cadmium sulfide (CdS), thallus sulfide, galena crystal, lead
telluride, and lead sulfide. Such cells require a supplementary voltage source,
and have good infrared sensitivity and high signal-to-noise ratio. They do not,
however, have the excellent frequency response of vacuum phototubes (Mark, 1956).
Moisture is also a major inhibitor of photoconductors, and destroys conductivity
(Zmuda, 1962). The best known solid-state photoconductor is the cadmium sulfide
cell (CdS), used today in many camera light meters. These cells have reached a
high degree of development within the last few years, and are excellent light-
control mechanisms. Below 5000 R, the photoconductivity of CdS remains constant
down to 2500 A. But, unlike most photoconductors, infrared illumination tends to
quench the photoconductivity above 5200 &R. Such cells are also Poe sensi-
tive detectors of X-rays and corpuscular radiation. A transport of 10~ electrons
has been demonstrated for a single X-ray quanta (Zworykin and Ramberg, 1949).

Photovoltaic cells.--Photovoltaic cells are cells capable of generating a
voltage when exposed to light radiation. This category includes the selenium
cells now used in such diverse applications as colorimeters, lighting controls,
and relay circuits (Sasuga, 1962). Another type of cell that fits the photo-
voltaic definition more closely than selenium cells is the silicon or solar cell,
commonly used in banks as battery cells for satellites. A silicon cell can
convert sunlignt directly into electricity and thus, when used with a highly
sensitive relay or meter, requires no supplementary power source.

Thermistors.--Thermistors are substances in which the electrical resistance
varies inversely with the temperature. They are solid-state semiconductors formed
from ceramic materials made by sintering mixtures of metallic oxides, such as
manganese, nickel, cobalt, or uranium (Thermistor Manual, Anonymous, 1962). Thern-
istors can be used either to control or measure temperatures, and they attain con-
siderable advantage over ordinary thermocouples in that neither polarity nor lead
length affects their operation; also, no reference temperatures or cold junction
compensations are required, as is the case with thermocouples. Their high sensi-
tivity, fast response, and small size make them extremely useful to entomologists
concerned with measuring and controlling microenvironment of small insect cages.
The thermistor's wide resistance change per degree change in temperature produces
excellent accuracy of measurement; i.e., 78 ohms per degree centigrade compared
with only 7.2 ohms for a platinum resistance bulb (Anonymous 1962).

alt=

Micro-ducers.--Micro-ducers are solid-state transducers which vary in
resistance over a wide range with a change in force or pressure. Rare earths are
processed with zirconium tetrachloride to produce resins, which undergo a change
in resistance with a change of pressure (Hefferline et al., 1960). Resistance
changes are not affected by temperature variations from -20° to 300° F., and the
transducers' reliability is not impaired by continuous usage. Clark Electronics
teformmertioctl! produce a pressure-sensitive paint from which hundreds of pressure
transducers can be made for experimental purposes. They are applicable to
measurements in the fields of motion, speed, density, vacuum, or pressure, and
can operate relays and circuits without amplification. They will operate from
either a.c. or d.c. voltage.

Circuits

Inexpensive recording and control circuits, that have been successfully used
in studying ecology and behavior of the corn earworm, are shown in figures 1 to
6. Variations or modifications of these circuits are found in the references at
the end of this paper, and entomologists will no doubt devise many new uses. It
is recommended that researchers interested in instrumentation obtain the publi-
cations listed (many of which are free from the manufacturers) and make up an
instrumentation looseleaf handbook.

The series circuit (fig. 1A) may be converted to a simple thermistor
circuit by the substitution of the appropriate thermistor for the manual variable-
control potentiometer R,. The battery, thermistor, and microammeter (Ro) or
microamp-recorder form @ simple series circuit. The thermistor may be mounted
at extreme distances from the circuit and recorder; e.g., up among the leaves of
a tree. The thermistor should be of high resistance, preferably above 100,000
ohms. Because of the high resistance, as long as the voltage remains constant,
the current flow will be determined only by the thermistor temperature, and any
change in the resistance of a long transmission line due to ambient temperature
will be negligible (Anonymous, 1962). The author and Mr. V. J. Valli of the
U.S. Weather Bureau have used this type of circuit to continuously record temper-
atures in the corn silk channel where the corn earworm feeds.

A bridge circuit may be constructed to form an even more sensitive
temperature-measuring circuit (Taylor, 1952). Besides temperature measurements,
the Thermistor Manual (Anonymous, 1962) lists the following diverse uses for
simple thermistor circuits: Temperature compensation, temperature control,
liquid level measurements, time-delay circuits, remote control, switching, power
measurements, voltage control, altimeters, and thermal-conductivity instruments.
Thermistors come in many sizes and shapes, and are thus easily fitted into
various insect-cage designs. Disks, washers, beads, glass probes, rods, matched
pairs, and probe assemblies are a few of the many configurations obtainable
(fig. 8). Most manufacturers stock mounting hardware, and mount configurations
for various types of thermistors.

Since the resistance of the thermistor is a function of its absolute temper-
ature, excessive electrical current will heat it above the ambient temperature,
causing a resistance drop.: For this reason, thermistors are tested with very
minute currents so that there will be no measurable increase in the thermistor
temperature. The values obtained are designated by the mathematical expression
Ro» and Ro values are usually given at a specified degree centigrade in the

-5-

manufacturer's table of thermistor stock. Resistance curves for various degrees
centigrade are also furnished.

Figure 2 illustrates an inexpensive actinometer using a photoconductive cell
for continuous recording of moonlight, daylight, or low-intensity, crepuscular
light (Callahan, 1964). The cadmium sulfide cell (CL 505L) is the control
resistance which, when dark, offers so high a resistance that very little current
flows in the recorder. As the cell is illuminated by more and more moonlight or
the rising sun, resistance drops, and higher currents reach the recorder. The
CL 505L has a light resistance of about 1500 ohms and a dark resistance of over
a million ohms. The values for the shunt resistors R, and R, were determined by
using Ohm's law. They are variable trimmer Pesietores so that values for extremely
low or high light intensity can be inserted in the circuit. This same circuit
illustrates a use for the photoyoltaic cell- The B10 is a photovoltaic solar cell
and operates a sensitive Sigma i 5ss 50-ohm relay, which cuts in and opens the
circuits when excessive sunlight reaches the cell. This prevents damage to the
recorder, which would draw excessive current under high-intensity light conditions.

The basic circuit without the protective sun cell device, but with a prism
over the CdS cell, is shown in fig. 9 as a dew recorder. A low-intensity light
source (a) is fixed at a far enough distance above the glass prism surface (b)
so that there is no heating of the prism. As moisture droplets form and disappear
from the glass surface, light is reflected in all directions, which breaks up the
base line of light. Figure 10 shows a recording of both moonlight (which took the
place of a fixed-light source in this test) and the formation of dew along the
moonlight base line. The recording can be seen rising at about 12:10 a.m. as the
moon tops some trees. The dew is represented by the broken dotted portion of the
moon base line, and’ can be seen from 12:35 to 1:05 a.m. and from 1:30 to 2:10 a.m.

Figure 3 illustrates a further use for such a circuit. A leaf is taped
above the prism, and a first-instar larva confined on the leaf to feed. A red
filter may be used to subdue the light. As the larva feeds, the leaf tissue
decreases and more light reaches the CdS cell, giving both a time and quantity
line on the recorder. This particular modification is extremely useful for very
small larvae.

Figure 4 illustrates the use of a Delco ® 1/ LDR25 high-wattage CdS cell as
a motor speed control. The 3000-ohm rheostat can be used to turn down the light
bulb, increasing the resistance of the LDR25, and slowing the motor. Various
filters could also be used between the light source and the cell and rotated by a
clock mechanism, causing the motor to slow down or speed up at various set, pre-
determined times. Almost any load could be substituted for the motor and
controlled by changing light intensity through the rotating filters. A further
use of such a high-wattage, CdS cell might be to hook it in series with a cage
light so that the intensity of an incandescent lamp in the cage would vary
proportionally to outdoor light shining on the cell.

I am at present constructing flight-activity cages in which the light is
continuously and gradually dimmed as the sun goes down. This enables me to
compare continuously varying light as it is found in nature, with the on-off
light situations that are usual in the study of diapause, et cetera. I believe
that the on-off light situation subjects the adults to a "light shock" phenomenon
that affects flight patterns and behavior of the adult earworm moth. It is only

25606

by gradually increasing and decreasing the light intensity in the cage, and at
the same time recording the variations with the actinometer that natural light
behavior patterns can be compared to the on-off light patterns of a restricted
laboratory situation.

Figures 5 and 11 show a circuit that is used in a moth-activity and flight-
behavior chamber designed by the author. It is a circuit adapted from the
International Rectifier Corporation's Solar Cell and Photocell Handbook (Sasuga,
1962) and is a transistorized relay switching circuit that utilizes an Al5
selenium photovoltaic cell. The Photocell Handbook gives many simple transistor-
ized circuits that can be easily wired, and would be useful to insect behaviorists
in diverse experimental situations.

The 50,000-ohm, washer-type, variable potentiometer (files 5) was constructed
from pressure-sensitive paint; it is possible to set the operating threshold of
the circuit by tightening the nut and bolt on the washer transducer. The 500,000-
ohm rheostat is a positive feedback resistor that balances the circuit for sharp
switching action and suppression of spurious oscillations. The photocell is
shown hooked up for switch-on with illumination, but by simply reversing the
photocell leads, switch-off may be accomplished with illumination. The circuit
is excellent for moth activity recordings, as the circuit is sensitive down to
1/2 foot-candle, which is well within the flight tolerances of almost all night-
flying moths. Since the circuit is transistorized, it is small enough so that
several can be mounted on the side of an activity chamber. The fast thyratron-
like action of the circuit makes it valuable for counting and timing flights with
an operational recorder. I have used it with a red filter over the light source
to monitor a feeding station and take flight photographs of moths (fig. 12). Two
or more cells may be mounted at either end of a flight chamber to count and time
visits of moths to food or oviposition and sex-attractance sites, thus making an
automatic olfactometer of the chamber. Since it is battery operated, it can be
used to record moth visits to flowers in the field.

The Amprobe recorder (fig. 9d) may be used as both a galvanometer-type
recorder and operation recorder by mounting an inexpensive marking pen stylus relay
above the pressure-sensitive paper. With this system, both varying light and
time of flight can be recorded from the flight chamber on the same recorder. It
is only necessary to hook a low-voltage, battery-operated relay across the
contacts of the 1000-ohm control relay, and adjust the marking pen so that it
strikes down, leaving a dot on the recorder paper.

Figure 6 shows a simple circuit for recording pressure parameters by
positioning a micro-ducer between the wings of a moth in fixed flight. A
pressure-sensitive-paint micro-ducer is mounted over the back of the insect, and
as the wings come together against the contact sides, a resistance change occurs
in the circuit and is recorded in microamperes on the recorder. The author is
still experimenting with this circuit. As Hefferline et al. (1960) point out,
the mounting of such transducers is a difficult problem, and to eliminate error,
they must be positioned so that the contactors (i.e., the wings) strike the
circuit at the same position and angle. Further experimenting with pressure-
sensitive paint may produce a reliable wing-pressure transducer.

The pressure-sensitive paint is applied between two metal conducting
surfaces, and may also be vacuum-coated to form a barometric pickup, or placed

=i etm

over a magnet with a soft iron contact on top to make a solid-state relay,
amplifier, or wind- and water-pressure indicator. The manufacturer lists some
of the following possibilities for imaginative experimenters: Measuring
mechanical force, motion, pressure, altitude, vacuum, strain, shock, impact,
acceleration, position, flow, vibration, weight, or thrust. It also has
possibilities for uses in automation, such as in the development of a solid-
state relay for use with counters, et cetera. The manufacturer makes several
different types of paints from O to 1 p.s-i., up to 0 to 100,000 p-s.i.
Transducers are also obtainable already mounted between disks or washers with
the leads soldered in place. As pointed out above, I have used a washer-type
transducer between a nut and bolt as a screwdriver- paisa potentiometer in
the photocell circuit.

There appears to be unlimited uses for such solid-state pressure mechanisms,
and since they require no amplification in most cases, it may be possible to
construct inexpensive apparatus for the study of moth aerodynamics. I once
tested the holding ability of corn earworm moths on different surfaces (Callahan,
1957) and the technique developed in that work might be improved by using such
a pressure transducer as a strain gage to more accurately measure the clinging
force of the moth on the surface.

The examples listed above are but a few of the many possible uses of
simplified semiconductor circuitry applicable to the study of insects. These
circuits are only as reliable as their voltage source. For most uses a battery
will suffice, providing it is constantly checked for stability and voltage. The
1.4-volt, button-type, mercury battery is excellent as a voltage source for most
of the circuits. An on-off switch should be included in all circuits, as con-
tinuous discharge will soon cause erratic recordings and require recalibration
of the circuit. Where long-period recording or continuous operation is desirable,
a low-voltage, efficiently regulated d.c. rectifier power supply may be required.
Many such stable rectifier circuits are given in the book, Metallic Rectifiers
and Crystal Diodes, by Conti (1958).

Read-out of circuits may be direct in microamperes, or it may be preferable,
as in the case of light, to convert microamperes to langley or foot-candle units.
Such calibrations may be made against a standard pyrheliometer or foot-candle
light meter (Callahan, 1964) and the calibration curve kept with the recorder.
For a list of conversion factors from unit to unit, the reader is referred 9
the booklet, Conversion Factors, published by the Sillcocks-Miller Company .2
Photometric units are completely defined in chapter 1 of the International
Rectifier Corporation's Solar Cell and Photocell Handbook.

It is hoped that this summary of semiconductor circuitry and its usages in
insect ecology and behavior will induce more entomologists to use the fine
electronic tools now available to biological scientists in conducting their
research.

REFERENCES CITED

*Anonymous
ff n.d./ Conversion factors. The Sillcocks-Miller Co. Maplewood, N.J. 16 pp.

*Anonymous
1962. Thermistor Manual. Fenwal Electronics, Inc. Framingham, Mass. 20 pp.

*Anonymous
1964. Micro-ducers. Clark Electronics Laboratories. Bul. 316, pp. 1-5.
Palm Springs, Calif.

*Aronson, M. H.
1962. Recorder Manual. Instruments Publishing Co., Pittsburgh, Pa. 65 pp.

Callahan, P. S.

1957. Oviposition response of the corn earworm to differences in surface
texture. Kansas Ent. Soc. Jour. 30(2): 59-63.

*Callahan, P. S.

1964. An inexpensive actinometer for continuous field recording of moonlight,
daylight, or low intensity evening light. Jour. Econ. Ent. (In
press.

Callahan, P. S.
1964. A photoelectric-photographic analysis of flight behavior in the corn
earworm, Heliothis zea, and other moths, with special reference to
a theory for electromagnetic radiation as an attractance force
between sexes. (In manuscript.)

*Conti, Theodore.

1958. Metallic rectifiers and crystal diodes. John F. Rider Publisher, Inc.
New York. 152 pp.

*Hefferline, R. F., Birch, J. D., and Gentry, Thomas.
1961. Simple transducers to detect or record operant amplitude. Jour. Expt.
and Analyt. Behavior (3): 257-61.

*Mark, David.
1956. Basics of phototubes and photocells. John F. Rider. Publisher, Inric.
New York. 128 pp.

*Sasuga, John.
1962. International Rectifier solar cell and photocell handbook.
International Rectifier Corp. El Segundo, Calif. 111 pp.

ATavallors die Gre
1952. Thermistors. Agr. Engin. 33(8): 502.

*Zmuda, E. I.

1962. Applications of the photoconductor. Sylvania Electric Products, ID eKSG 6
Electronic Tube Division, Teterboro, N.J. 9 pp.
*Zworykin, V. K., and Ramberg, E. G.
1949. Photoelectricity and its application. John Wiley and Sons, Inc. New
York. 49h pp. 9

R
2 Figure 1.--Series and series parallel
circuits.

A. Ry = manual variable potentiometer

A SERIES (30,000 ohms); R, = microammeter
or microampere recorder (7400 ohms).

R, = manual variable potentiometer
(35,000 ohms); R5 = shunt resistor
(200 ohms); Ra— microammeter or
microampere recorder (7400 ohms).

B SERIES PARALLEL

CL 505 L

Figure 2.--Actinometer or dew recorder circuit. CL505L = cadmium-sulfide
cell; R,= Sigma 5ss 50-ohm relay; Bl1O= International Rectifier selenium sun

cell; Ry — O-50 ohm, trimmer potentiometer; Ae = 0-500 ohm trimmer potentiometer;
at

S, = 3 position shunt switch; 52 = on-off switch.

Slee

RECORDER

(dS CELL

Figure 3.--Larval leaf-feeding recorder. Same as figure 9,
dew recorder with leaf over prism.

110 V AC 3000 ~ << LOR 25

FILTER
1500 ~

MOTOR

4

Figure 4.--Control mechanism for motor or other electrical
load, using a 25-watt, Delco, cadmium-sulfide cell.

Sees Be

Figure 5.--Two-transistor control relay, utilizing an
A 15-M selenium photovoltaic cell for the light control.

www RECORDER

6

Figure 6.--Micro-ducer pressure-sensitive transducer
mounted between a corn earworm moth's wings to record force
of wing beat above back. The 100,000-ohm, variable rheostat
allows for calibration of range extremes on the recorder.

Pa oe

Figure 7.--(a) Bottle of pressure-sensitive paint; (b) B2M International
Rectifier selenium sun cell; (c) A 15-M selenium photovoltaic cell; (d) 1.4-V.
button mercury battery; (e) pressure micro-ducer mounted in series circuit with
rheostat, battery, and microammeter.

a eo

oe:

Se eee eee ee eee eee ee ee ee ee cae a a a Seca ec acs enue cee as cent aur uu ean dom Salis Se

INCHES ’

Figure 8.--Thermistor configurations. (a) Disk thermistor for surface temper-
ature measurements; (b) hypodermic-type thermistor, used in corn silk channel by
the author; (c) flexible probe; (d) bead probe.

Saleh

Figure 9.--Dew recorder, circuit No. 2 with prism over the CdS cell. (a) Fixed

light source; (b) prism; (c) circuit; (d) Amprobe 7400-ohm,
recorder; (e) adjustable transformer for light source.

AM ae
3 boa PL ie
i :
oe : E
NS eeESeNS es oS ss oth — el ap
7 8 1 { 12 1 2
ss He cee | *
S d, e i
BS oe } AM ) z
—s pacer ae
s 8 Hi “iz } rae 3 gis 4
oa ; 4 os cr 8 RAS.
2 oy so is Roe Bes ©
SZ 4 hie Y aM re PA zg Belk
24 so) _n /
i: tee $ = 7
7
aoe eae ; :
oe xs Bs - ra 9
: t we dba
—— SC ees
2 = Stig
5 B 12 i 3 ws 4
: 5 ¥ 8
x ‘ “ : Ly
IP a ry ee al |? Apo ™ 2 to ¥ =
WAY Oca A: I DY ARTE Peal) HOGA , /

0-50 microampere

Figure 10.--Recording
of dew formation on
night of Oct. 4 1963)
from 10:10 p.m.
(bottom strip) to
2:10 a.m. (top strip).
The line represents
moonlight and not a
fixed light source.
The rise in the line
at 12:05 a.m. re-
presents the moon
climbing above the
trees. Dew is re-
presented by the
breaking up of the
line. The first
period (3rd strip)
lasts for 30 minutes
from 12:35 a.m. to
1:05 a.m., and the
second longer period
(top strip) from

1:30 on.

Figure 11.--Flight chamber for studying moth aerodynamics. (a) Roa battery;
(ob) circuit (fig. 5); (c) A 15M selenium cell; (d) connection of strobe light;
(e) across relay contacts of the Sigma 11f, 1000-ohm relay of circuit (fig. 5).

15

Figure 12.--White-
lined sphinx ina
banking turn. The
low-intensity red
light beam crosses
from the right and
focuses on A 15M cell
at left. Although
the light intensity
is low, the strobe
fired even though
the cell was partial-
ly blocked by an
arctiid. Because
the cell operates at
low light levels,
the camera shutter
is left open and the
film does not be-
come fogged. The
strobe light alone
takes the picture.
(Callahan, 1964).

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