64 



Emission and Transmission of Heat 



ductivity from the same elements; but I have employed a differ- 

 ent and much more exact method of measuring the temper- 

 ature of the exposed surface. Opposite the heated plate was 

 placed a vessel of the same form filled with water; the opposing 

 surfaces of the two vessels were covered with paper, and the 

 poles of a very sensitive thermopile, connected with a galva- 

 nometer, were placed exactly equidistant from both; it is evident 

 that when the needle of the galvanometer was at zero, the tem- 

 perature of the exposed service of the plate was the same as that 

 of the water in the vessel. 



853. Figure 175 is a plan of the apparatus, figures 176 and 

 177 elevations of the two longer sides, figure 178 a section per- 

 pendicular to the eleva- 

 tions . In all these figures 

 the same letters indicate 

 the same objects. ABC 

 D figure 175 is a rectang- 

 ular closed tank of sheet 

 lead full of water; it is 

 surrounded by a wooden 

 box X X X X; the bot- 

 toms and ends of these 

 two vessels are separated by spaces of two and a half inches. 

 The long sides of the tank are only partly covered with wood. 

 The spaces A X X C 

 and B X XD between 

 the ends of the tank 

 and the box are pro- 

 vided with a great num- 

 ber of metal strips sol- 

 dered vertically on the 

 tank, the object of this 

 is to impart to the air 

 passingdownthespac- 



esAXXCandXX Plg< I?6 



D the temperature of 



the water in the tank. G G and H H are two vertical rectangular 

 conduits passing entirely through the tank and communicating 



