402 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 17 



The galvanometer A is essentially a millivoltmeter having a short 

 contact arm or boom in place of the usual pointer, and two contact 

 stops. It differs from the White-Adams instrument in that contact 

 is made as soon as the boom reaches one or the other stop. B is an 

 ordinary polarized telegraph relay, and C a "main line" telegraph re- 

 lay. . The main relay C is operated by current taken directly from the 

 line through the resistance coils Ri and Ro. It opens when its coil 



/' 



Fig. 1. — Schematic diagram of furnace temperature regulator. 



is short-circuited by the contacts of the polarized relay B. The gal- 

 vanometer contacts are so connected that the movements of the 

 galvanometer place the polarized relay B either in parallel with the 

 main relay C or in parallel with 150-ohm resistance Ri. The opera- 

 tion of the polarized relay, however, immediately short-circuits the par- 

 ticular coil with which it has just been connected, thus stopping the 

 flow of current through the contacts of the galvanometer. 



This arrangeinent was intended to prevent these contacts from be- 

 coming welded together, but was found to be insufiftcient. There- 

 fore, the secondary (low-voltage winding) 5 of a "bell-ringing" 

 transformer was connected in series with the galvanometer, and the 



