136 Dr. Akm's further Statements concerning 



A second analysis gave the following confirmatory results 

 Tin 79-52 



Lead . . 



Copper 



Iron 



Arsenic 



Insoluble gangue 



1971 

 009 

 0-19 

 trace 

 0-49 



10000 



XXIII. Further Statements concerning the History of Calcescence. 

 By Dr. C. K. Akin*.j 



THE last Number of the Philosophical Magazine contains an 

 article " On the History of Negative Fluorescence/' by Prof. 

 Tyndall, to which I intend herewith to reply. As this is a per- 

 sonal discussion, of course I shall have to allude to personal 

 matters ; but, in doing so, I shall endeavour not to imitate the 

 language adopted by Prof. Tyndall towards myself, more or less, 

 throughout his paper. In stating this, however, I do not wish 

 to complain of Prof. Tyndall ; for, besides that language of this 

 kind always recoils upon the person who uses it, he has adopted 

 the same tone in his discussions with Professors Tait and Thom- 

 son, and in such excellent company I can very well bear Prof, 

 TyndalPs contumely. 



1. It is now probably from eight to ten years ago that, as a 

 student at the University, and the notions which I was then being 

 taught regarding the nature of heat and radiations being rather 

 vague and inaccurate, I proposed to myself the "conversion of 

 heat into light " as a problem to be solved in the course of my 

 future scientific career. In the year 1860 I attended the Meet- 

 ing of German naturalists at Konigsberg, at which Professor 

 Knoblauch communicated some new researches of his on the 

 interference of Herschellic rays. I then observed to one of the 

 Konigsberg Professors how much more simple experiments of 

 this kind would be if it were possible to convert Herschellic rays 

 into visible or Newtonic rays, in a similar manner to that in 

 which Prof. Stokes had shown how to convert Ritteric rays into 

 Newtonic rays. In February 1862 I made a stay at Cambridge, 

 when I had the advantage of seeing the principal experiments on 

 fluorescence performed by Prof. Stokes himself. Having then 

 in my possession a little German treatise which contained a short 

 account of all that had been published at that period on the sub- 

 ject of fluorescence, I began to peruse it; and in the course of 

 that perusal the main ideas which I have since published on the 

 * Communicated by the Author, 



