Emission and Transmission of Heat 



Fig. 177 



Fig. 178 



by the space beneath it with the openings A XX C and B XX D. 

 II is an opening in the tank but it does not penetrate completely 

 through it. K K (fig 178) are two horizontal tubes with the 

 same axis and of the same diameter, open at both ends, LLLL 

 are openings eight inches square formed in the long sides of the 

 tank, which pierce from the outside into the conduits G G, H H. 

 These conduits, cylinders and openings are surrounded by water, 

 MMMMo.ro. funnels surmounting openings through which pass 

 agitators. A 7 " TV are openings for thermometers. O is a thermo- 

 pile in the enclosure //, opposite the common axis of the two 

 tubes K K and equidistant from their inner ends; its poles are con- 

 nected with a very sensitive galvanometer not shown in the figures. 

 /'/'are substantial double screens, capable of movement about 

 the axis Q Q, and intended to intercept the rays of heat reaching 

 the thermopile through the tubes K K. The openings LLLL 

 receive the bodies whose surfaces act upon the thermopile; but as 

 these surfaces must always be at the same distance from the ther- 

 mopile, the inner edges of the openings LLLL are provided 

 with four stops RRRR against which the bodies are supported. 

 Figure 179, representing one side of the tank when the opening 

 LLLL is empty, shows the arrangement of these stops. 



854 . One of the openings L L L L is always occupied by 

 a copper vessel 6* T (fig 178) full of water, and provided with two 

 agitators and a very sensitive thermometer; a part of its lower sur- 

 face is so arranged as to be easily heated by an alcohol lamp. This 

 vessel is surrounded by a frame of fir wood, which separates it 



