Prof. Tyndall on (he History of Calorescence. 227 



more than fair; in relation to him it has proved to be worse 

 than useless. 



Late in the day of the 29th of October, I obtained the incan- 

 descence of platinum foil by the dark rays of the electric light. 

 The layer of iodine, however, was too thin to wholly intercept 

 the light, while the battery had been enfeebled by long-continued 

 previous action. On the following morning it was freshly charged, 

 the number of cells being increased from fifty to sixty. Removing 

 from the back of the camera the little reflector which I had made 

 use of in 1862, I mounted it on a retort-stand, and with it 

 converged the rays from the lamp. The mirror was silvered 

 behind, and the reflected rays had therefore to pass to and 

 fro across a plate of glass of considerable thickness. Not- 

 withstanding this, however, and the employment of a much 

 thicker layer of dissolved iodine, the platinum, when placed in 

 the dark focus of the mirror, became vividly incandescent. 

 Almost immediately after the performance of this experiment 

 I found Dr. Akin in the library of the Royal Institution. With- 

 out a moment's hesitation I invited him to accompany me to the 

 laboratory, and there almost simultaneously with myself he saw 

 the result which I had obtained*. 



Not one word of remonstrance or complaint escaped him on this 

 occasion ; not a syllable to indicate that he believed me in any 

 way pledged to him. He made some critical remarks as to the 

 experiment being made in daylight. He was moreover struck 

 with the thickness of the layer of iodine employed, observing 

 that the layer used by him at Oxford was a thin one, which 

 did not cut off the light. He finally expressed himself delighted 

 to see the experiment, and we quitted the laboratory together. 

 I walked with him upstairs, and there at the eleventh hour ex- 

 pressed my desire not to interfere w T ith him, and to leave, if he 

 wished it, the subject still in his hands. His reply was, " It will 

 all depend on the manner of publication." Knowing my own 

 willingness to do him the amplest justice in any publication of 

 mine, I responded, "You shall see my manuscript before I 

 publish." 



My intention when I parted from Dr. Akin was to give a 

 brief account of the experiment at the first meeting of the Royal 

 Society, but I had not definitely made up my mind. On the 

 evening of the day to which I now refer I thought and spoke 

 of associating myself with Dr. Akin for the further prosecution 



* Dr. Akin had informed me that he was collecting materials for a "His- 

 tory of Force," and needed access to a good library. Deeming his work both 

 useful and honourable, to enable him to prosecute it I introduced him to 

 the libraries both of the Royal Institution and the Athenaeum Club. 



