126 



BACTERIOLOGY 



is made to operate a horse-shoe magnet> and another part is 

 conducted through the lamp used for heating. 



The accompanying diagram (Fig. 53), will serve to show the 

 arrangement. 



A telegraph key is used to supply the horse-shoe magnet 

 which is inserted in the heating circuit in such a way that when 

 the armature is attracted toward the magnet the circuit is com- 

 pleted and the lamp is consequently lighted. The part of the 

 current, a, supplying the magnet first passes through a small 



Re9ia *anoG -coife 



Thermorea/u/af-or 

 Pig. S3- — Diagram of electric regulator for low-temperature incubator. 



lamp and through two resistance coils so as to reduce the current. 

 It then passes through the magnet, and is continued on to the 

 set-screw, b, which is so placed that when the thermoregulator 

 comes in contact with it the circuit is . complete. The regu- 

 lator consists of a strip of hard rubber and a strip of brass riveted 

 together. One end is fixed, while the other is free, and when it 

 is heated it tends to bend toward the metal side, when it cools it 

 bends toward the rubber. The brass strip is 15 inches long, )4 

 inch thick, and 3^ inch wide; the rubber strip is ^-i inch thick, K 

 inch wide, and a little less than 15 inches long. In the diagram 

 the end is fixed at d and is free at i. When it is heated, the free 



