140 



water. Tlie hummer circuit is closed by tlie switcli on tlae left side of the 

 cabinet. This switch opens automatically when released. Should the hummer 

 not start on closing the switch after two or three trials, the box containing the 

 hummer should be tapped while the switch Is held closed. 



POWER CIRCUIT 



Electric power for the entire operation of the apparatus is taken from the 

 110-120 volt direct current supply. This serves the following purposes : 



1. Operation of the stirring motor. 



2. The heating elements to maintain the bath at a desired temperature. 



3. Heating lamps to keep inside the cabinet dry. 



4. About 3 volts for the operation of the I'elay. 



5. About 10 volts for the operation of the hummer which supplies tlie 



1.000 cycle test current to the bridge. 



DfQjmm of Connecti' 

 HUMMER 



Feb. 16.1923. 



LMI 





If one side of the power circuit of the ship is grounded, it is advisable ti> 

 nuike tlie connection in such a way as to bring the relay and hummer to pruc- 

 t cally ground potential. This not only materially reduces the chances foi- 

 getting an electrical shock, but also the fire hazard. The power circuits 

 should be left closed for the greater part of each day to preserve the insula- 

 tion <»f the entire apparatus. A diagram of the power circuit is shown in dia- 

 gram No. 4. The heaters for the bath are connected into the circuit by the 

 upi)er and middle snap switches on the right side of the left-hand compart- 

 ment <»f the cabinet. The middle switch is in series with the relay and so is W\v 

 one to be kept at tlie " On " position when it is desired that the temperaturt^ 

 of the bath be regulated. The top switcli is normally kept in the '• Off " posi- 

 tion, as only one of the heaters is regularly required. This second heatei- 

 may be u.sed to bring the bath quickly to the regulating temperature, or wlicn 

 iitherwise needed. 



