316 A ction of an Intermittent Beam of Radiant Heat. [Jan. 13, 



energetic absorber of the luminous rays ; and to them, when suddenly 

 converted into thermometric heat in the body of the vapour, I thought 

 the sounds might be due. 



Between the flask containing the bromine and the rotating disk, I 

 therefore placed an empty glass cell : the sounds continued. 1 then 

 filled the cell with transparent bisulphide of carbon : the sounds still 

 continued. For the transparent bisulphide I then substituted the 

 same liquid saturated with dissolved iodine. This solution cut off the 

 light, while allowing the rays of heat free transmission : the sounds 

 were immediately stilled. 



Iodine vaporised by heat in a small flask, yielded a forcible sound, 

 which was not sensibly affected by the interposition of transparent 

 bisulphide of carbon, but which was completely quelled by the iodine 

 solution. It might indeed have been foreseen, that the rays trans- 

 mitted by the iodine as a liquid, would also be transmitted by its 

 vapour, and thus fail to be converted into sound.* 



To complete the argument : — While the flask containing the 

 bromine vapour was sounding in the intermittent beam, a strong 

 solution of alum was interposed between it and the rotating disk. 

 There was no sensible abatement of the sounds with either bromine 

 or iodine vapour. 



In these experiments the rays from the lime-light were converged 

 to a point a little beyond the rotating disk. In the next experiment 

 they were rendered parallel by the mirror, and afterwards rendered 

 convergent by a lens of ice. At the focus of the ice-lens the sounds 

 were extracted from both bromine and iodine vapour. Sounds were 

 also produced after the beam had been sent through the alum solution 

 and the ice-lens conjointly. 



With a very rude arrangement I have been able to hear the sounds 

 of the more active vapours at a distance of 100 feet from the source 

 of rays. 



Several vapours other than those mentioned in this abstract have 

 been examined, and sounds obtained from all of them. The vapours 

 of all compound liquids will, I doubt not, be found sonorous in the 

 intermittent beam. And, as I question whether there is an absolutely 

 diathermanous substance in nature, I think it probable that even the 

 vapours of elementary bodies, including the elementary gases, when 

 more strictly examined, will be found capable of producing sounds. 



(Received January 14.) 



Note. — With some of the strongest sounds, which were audible when 

 the ear-tube was entirely withdrawn from the ear, I tried to obtain the 



* I intentionally use this phraseology. 



