Radiant Heat, and its Conversion thereby into Sound. 449 



or account for, the differences between my friend and myself, 

 I wrote to him proposing an exchange of apparatus — that he 

 should send his to London, and I mine to Berlin. I after- 

 wards had a facsimile of his apparatus constructed in London, 



Fi°\ 2. 



< 



and satisfied myself by actual trial that it was really ham- 

 pered with the defects I had ascribed to it. By means of the 

 striae of incense smoke and of chloride of ammonium, the fact 

 of convection in air was rendered plainly visible to the eye ; 

 while the behaviour of hydrogen, under like circumstances, 



