the History of Calcescence. 137 



transmutation of rays occurred to me*. I immediately commu- 

 nicated on the subject with Prof. Stokes, hoping- that he would 

 enable me to bring my speculations to the test of experiment. 

 Prof. Stokes expressed himself in very high terms on the im- 

 portance of the subject — terms which I have since often repeated 

 to others, and which have frequently encouraged me to persevere 

 when my patience was nearly exhausted ; and when, towards 

 midsummer 1862, I left Cambridge, he was good enough to ex- 

 press his regret that it had not been in his power to give me an 

 opportunity of making the experiments I had proposed. In No- 

 vember of the same year, i. e. 1862, I went to reside at Oxford, 

 and so much was my mind engrossed by the matter in hand, 

 that the very first time I met Mr. Griffith, then, as now, Deputy 

 Professor of Experimental Philosophy in the University, I 

 broached the subject to him, when I was greatly pleased 

 to find that the matter interested him, and that he was ready 

 to make experiments on it with me. Consequently, in the 

 month in question, or early in the December following, we 

 made some trials with the oxyhydrogen jet ; and as these gave 

 no satisfactory result, we began to make experiments on the sun 

 a short time after. These latter experiments were continued till 

 June 1863, when I drew up a paper on the subject, which I for- 

 warded to the Royal Society. Being called by urgent private 

 matters to town at that time, it was arranged that, during the 

 week or ten days intervening, the experiments, which appeared 

 then to be in a very forward state, should be completed, so that 

 an account of the result might be presented by me to the Royal 

 Society at the last Meeting of the then session. The expectation 

 founded on this arrangement, however, was not fulfilled, and I 

 was consequently advised to withdraw also the introductory 

 papers already forwarded for communication to the Royal 

 Society. Although, in consequence of private circumstances 



* I may as well state now that the article on fluorescence in Cornelius 

 and Marbach's Physical. Lexicon (the work being one intended for popular 

 circulation and for reference, not for perusal) became first known to me 

 from M. Emsmann's paper on " Negative Fluorescence," published in Pog- 

 gendorfFs Annalen in 1861. It so happened that, at the time when this 

 last-mentioned paper appeared, I was staying at Paris, where I had no access 

 to Poggendorff 's Annalen; and when in the following spring I had an op- 

 portunity of seeing the Annalen at the University Library at Cambridge, 

 the volume in which M. Emsmann's paper was published was with the 

 binder ; so that the paper became actually known to me only in the winter 

 of 1862-63 at Oxford. In my paper in the Reports of the British Asso- 

 ciation, in which I have duly adverted to M. Emsmann's publications, I did 

 not think it necessary to mention these facts, as they were of no scientific, 

 but only of personal interest. For an appreciation of the contents of M. 

 Emsmann's paper I must refer for the present to the historical Appendix 

 in the Reports of the British Association for 1863, p. 99. 



