Radiant Heat, and its Conversion thereby into Sound. 497 



worked brass plate 1 millimetre thick, perforated like c c. A 

 portion of this middle plate is cut away, opening a passage 

 into the interior of the cell. Through this passage the cell is 

 filled with liquid by means of the funnel /'. The cell is placed 

 on a platform P P riveted onto the double brass screen S S. 

 The source was placed at A, and the thermopile with its 

 blackened tube at B. It is not necessary to figure them. 



The needle being brought accurately to zero by the com- 

 pensating-cube when the cell was empty, liquid sulphuric 

 ether was poured in. The consequent deflection was 



42°. 

 Here vapour absorption and liquid absorption were so nearly 

 alike as to stimulate me to further efforts. The entry in my 



Fig. 5, 



note-book on the 22nd ends with the remark : — " I purpose 

 repeating this experiment on Monday, with the view of ren- 

 dering the result secure. " 



