The type used was manufactured by the Heiland 

 Corporation, Denver, Colorado. 



Buzzer.- -A buzzer was incorporated in 

 the device to warn the operator when one or 

 both cameras were not wound. A common buz- 

 zer, operated from a 4-1/2-volt batter was 

 used. Tlie battery and the buzzer were strapped 

 to tlie strobe light assembly. 



Digital -register . - -An electrically oper- 

 ated digital -register was placed on the base to' 

 number each picture and each fish consecutively 

 so that the left and right pictures could be 

 matched when the films were read. The digital- 

 register used was a Mercury model manufactur- 

 ed by the Production Instrument Co., Chicago, 

 Illinois. 



Modified switch . --A modified lever 

 switch was used to trip the solenoids and the 

 digital-register in that order. That is, two con- 

 tacts were made, one preceeding the other, 

 each time the switch was thrown. In this way, 

 the number on the register was recorded in the 

 picture just before the number changed. 



Wiring 



The wiring system consists of four cir- 

 cuits: (1) The strobe light circuit, (2) the 

 solenoid circuit, (3) the buzzer circuit, and (4) 

 the digital -register circuit. Figure 16 is a 

 block diagram of these circuits. 



POWER PACK 



ncur« 16 .— aiock dlMgnm of vlrlng tjitw. 



The strobe light circuit is connected to 

 the X side of the two cameras . Note that one 

 part of this circuit is the "metal frame" --the 

 device itself. When the shutters of both of the 

 cameras are not cocked, the circuit is closed 

 or continuous because the X contacts in the 

 shutters are grounded through the bodies of the 

 cameras to the metal frame. When the shutters 

 are cocked, however, tlie circuit is open, or 

 not continuous, because the X contacts are no 

 longer grounded to the "metal frame". If the 

 shutters of both cameras have been cocked, the 

 strobe light can flash only after both shutters 

 have been released or tripped by the solenoids 

 which react almost simultaneously. The shutters 

 were set to remain open 1/25 of a second after 

 the circuit was closed to assure that both shutters 

 were still open when the strobe light flashed. 



Now if one camera were to remain un- 

 cocked, the strobe light and the camera with 

 the cocked shutter would still operate. In other 

 words, the operator could forget to wind one 

 camera and the mistake would go unnoticed. 

 Because of this the warning buzzer was installed 

 so that when one or both of the cameras were un- 

 wound, the buzzer would sound. One side of the 

 buzzer circuit is connected to the M synch of the 

 two cameras, and the other side is grounded to 

 the"metal frame" . The circuit is completed 

 whenever either shutter is not cocked. 



The solenoid circuit is closed when the 

 first contact is made in the modified switch. 

 The digital-register circuit is closed when the 

 «»''ond contact is made. The time delay between 

 making of the two contacts allows the picture 

 le taken before the register is advanced. The 

 tch used is #3004, manufactured by Switch - 

 ft Incorporated, Chicago, Illinois. 



TECHNIQUE OF USE 



Determining longitudinal distances be- 

 en two points consists of three major steps: 

 Taking the pictures, (2) reading the filn\ and 

 calculating the longitudinal distances . 



Taking the Pictures 



Taking the pictures consists of three 

 3S: (1) Assembling the device, (2) loading 

 adjusting the cameras and connecting the 



