368 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



firmly to the front of the wooden case. The side tube at E communi- 

 cates with the mercury chamber of the iron box of the heater. The glass 

 tube at B is .2 cm. in diameter at the upper part, the lower part being 

 much larger. 



A platinum wire F is held in place by a screw in the hard rubber 

 block G. The mercury rising by the expansion completes the relay 

 circuit at F, and the heating current is either cut off or reduced until the 

 apparatus cools off again. The screw in the lower part of the chamber 



A 

 A 



R 



K 



B B 



L- 



0» 



L- / w\aJwvw\m 



a 



Figure 4. 



enables the capacity to be suited to the temperature desired. The total 

 capacity of this chamber is about 20c.c, the expansion of the mercury 

 at 300° being about 18 c.c. The screw is three-fourths of an inch in 

 diameter and the pitch is sixteen threads to the inch. The glass tube is 

 cemented in with silicate of soda and the screw is packed with rubber 

 washers held between leather ones. The tube communicating with the 

 iron box is of steel about .5 cm. in diameter. A rise of temperature of 

 one degree causes an ascension in the glass tube of about 2 cm. With 

 the regulator cutting off the entire current, the regulation is within 



