ISogal institution of ©teat Britain* 



WEEKLY EVENING MEETING, 



Friday, April 8, 1881. 



George Busk, Esq. F.E.S. Treasurer and Vice-President, 



in the Chair. 



Professor Tyndall, D.C.L. F.E.S. M.B.L 



The Conversion of Badiant Heat into Sound, 



The Eoyal Society has done me the honour of publishing a long 

 series of memoirs on the interaction of radiant heat and gaseous 

 matter. These memoirs did not escape criticism. Distinguished 

 men, among whom the late Professor Magnus and the late Professor 

 Buif may be more specially mentioned, examined my experiments, and 

 arrived at results different from mine. Living workers of merit have 

 also taken up the question, the latest of whom,* while justly recog- 

 nising the extreme difficulty of the subject, and while verifying, so 

 far as their experiments reach, what I had published regarding dry 

 gases, find that I have fallen into what they consider grave errors in 

 my treatment of vapours. 



None of these investigators appear to me to have realised the 

 true strength of my position in its relation to the objects I had in 

 view. Occupied for the most part with details, they have failed to 

 recognise the stringency of my work as a whole, and have not taken 

 into account the independent support rendered by the various parts of 

 the investigation to each other. They thus ignore verifications, both 

 general and special, which are to me of conclusive force. Neverthe- 

 less, thinking it due to them and me to submit the questions at issue 

 to a fresh examination, I resumed some time ago the threads of the 

 inquiry. The results shall in due time be communicated to the 

 Eoyal Society ; but meanwhile I would ask permission to bring to the 

 notice of the Fellows a novel mode of testing the relations of radiant 

 heat to gaseous matter, whereby singularly instructive effects have 

 been obtained. 



Last year I became acquainted with the ingenious and original 

 experiments of Mr. Graham Bell, wherein musical sounds are obtained 

 through the action of an intermittent beam of light upon solid 

 bodies. From the first I entertained the opinion that these singular 

 sounds were caused by rapid changes of temperature, producing 

 corresponding changes of shape and volume in the bodies impinged 



* Lecher and Pernter, • Philosophical Magazine,' January, 1881 ; ' Sitzb. der 

 k. Akad. der Wissensch. in Wien,' July, 18SU. 



Vol. X. (No. 76.) n 



