230 Prof. Tyndall on the History of Caloresccnce. 



they had not been, the assumption of any such right of exclu- 

 sion is inadmissible. 



2. Dr. Akin affirms that he closed with alacrity with a pro- 

 position of mine to work out, in conjunction with him, a certain 

 subject. 



But Dr. Akin admits that he did not " close " with my first 

 proposition, on account of his tie to Mr. Griffith. He further 

 admits that he declined the "triple alliance " between Mr. 

 Griffith, Dr. Akin, and myself, which was next suggested by me. 

 Finally, he produces no evidence to show that I proposed or 

 accepted any other arrangement ; and I categorically deny that 

 any other arrangement was proposed or accepted by me. 



3. Dr. Akin's words imply that I have availed myself of his 

 ideas or suggestions, to anticipate his results. I answer thus : — 



It has been shown in the foregoing article that early in the 

 year 1862 I formed foci of invisible rays, and also illustrated in 

 my public lectures the heat of such foci ; that I employed for 

 this purpose the condensed rays of the electric light, and inter- 

 cepted the luminous part of the radiation by an absorbent of 

 extraordinary properties discovered by myself. 



Sir William Herschel had tried to render the ultra-red rays of 

 the solar spectrum visible by condensation, having first sepa- 

 rated them, by prismatic analysis, from the visible rays. But 

 the idea of forming intense foci of invisible rays by concentrating 

 the total radiation of a luminous source, and removing the visible 

 rays by an absorbent, is, I believe, entirely mine. 



4. In the autumn of 1863 Dr. Akin proposed to obtain an 

 intense focus of invisible rays by converging the sun's beams 

 and intercepting the luminous part of the radiation by absorb- 

 ents which he did not name. In making this proposition, Dr. 

 Akin had, without a word of acknowledgment, appropriated an 

 idea which I had in substance enunciated and applied more than 

 a year and a half previously. 



5. The only particular in which Dr. Akin was in advance of 

 me — a nd this not in thought, but in publication — was that he 

 was the first to express the belief that the dark rays of the sun, 

 when detached from the luminous ones by my method, would be 

 competent to raise platinum-foil to incandescence ; and that if 

 they did so we should have for the extra-red end of the spec- 

 trum phenomena analogous to those of fluorescence. 



6. In consequence of the precision with which he had enun- 

 ciated this idea, and also in part on account of his being a 

 foreigner, working, as I conceived, against difficulties in this 

 country, I somewhat Quixotically permitted him during the 

 whole of last summer to pursue his idea undisturbed. He had 

 tried, failed, and reported his failure to the British Association 



