46 Prof. Tyndall on the History of Negative Fluorescence, 



nology for the phenomena of radiation. The changes of refran- 

 gibility possible to light and radiant heat were afterwards dis- 

 cussed, and an experiment was described, by which the author 

 proposed to convert the ultra-red rays of the spectrum into visible 

 ones. 



In that article there was no mention of the form of conversion 

 which I thought had been established by myself; and having at 

 that time occasion to write to the editor of the c Saturday Review/ 

 I mentioned, in my note to him, my having already accomplished 

 that which Dr. Akin proposed to accomplish. I informed him 

 that my solution was already some months old, aud was now on 

 the verge of publication. I requested him, moreover, if he thought 

 fit, to show my note to Dr. Akin. 



These facts are distinctly in the recollection of the Editor of 

 the ' Saturday Review/ who is perfectly willing to corroborate 

 what I have here stated. 



The supposed change of period exhibited by a platinum wire 

 in a hydrogen-flame, constituted a brief episode in my memoir 

 on i( Molecular Physics," read before the Royal Society on the 

 17th of March 1864. Up to that date I had not the slightest 

 notion that Dr. Akin had ever alluded to the subject. During 

 the exposition of my paper I referred pointedly to Prof. Stokes, 

 with the view of eliciting his opinion as to the reality of the 

 conversion. That opinion, clearly expressed and ably sustained, 

 was not favourable to the conclusion at which I had arrived. 

 Prof. Stokes reasoned thus : — " When oxygen and hydrogen 

 clash together to form aqueous vapour, vibrations of the respec- 

 tive atoms, in short periods, result; but these vibrations of the 

 atomic constituents are soon imparted to the molecules of the 

 compound formed by their union. Aqueous vapour constitutes, 

 in fact, the c ashes ' of a hydrogen-fiame ; on these ashes the 

 rapid vibrations of the single atoms are expended, thus produ- 

 cing heat of lower refrangibility. When a platinum wire is 

 plunged into a hydrogen- flame, it simply takes up the vibra- 

 tions which, in its absence, are imparted to the ashes ; hence the 

 possibility that, in its case also, we have a lowering, instead of a 

 raising of the refrangibility." In reply to this striking argu- 

 ment, for which I was quite unprepared, I urged that the plati- 

 num might be brought to incandescence at some distance above 

 the tip of the hydrogen-flame, where the vibrations of the atoms 

 might fairly be supposed to have already expended themselves 

 upon the vapour-molecules. Prof. Stokes, however, retained 

 his opinion that the experiment was altogether inconclusive as to 

 the real point in question. 



After the reading of my paper, I went to the Isle of Wight, 

 and, while there, an abstract of the paper was published in the 



