THK PHOSPHOROGENIC RAYS. 



972. Nevertheless, this same sulphuret, carried into the sunshine, phosphoresces power- 

 fully under glass, apparently showing that there is a difference between the phosphoro- 

 genic emanation of the sun, for thus M. BECQUEREL terms it, and that of an electric spark. 



973. On this radiation, as it conies from the sun, M. BECQUEREL has treated in his pa- 

 per, of which a translation is given in Taylor's Scientific Memoirs (vol. iii., part 12). 

 He determines the place of the phosphorogenic rays in the spectrum after they have 

 passed through a glass prism, and shows that the fixed lines which occur in the chem- 

 ical spectrum, occur also among these phosphorogenic rays. 



974. In passing, I may mention that, at the time I published my account of these 

 fixed lines (Phil. Mag., May, 1843), I had no idea that any other chemist had seen 

 them. It, of course, soon appeared that M. BECQUEREL had some months previously 

 given an account of them to the French Academy. My result was wholly independ- 

 ent, and without any knowledge of his. On comparing the two papers, it will be seen 

 that there is a strong coincidence, not only in the manner of the experiment, but even 

 in the very phrases of description. It is this which has drawn these passing remarks 

 from me. Men who are pursuing the same object, and using the same resources, will 

 employ even words that are alike, though they speak languages that are different, and 

 live thousands of miles apart. 



975. On examining the plate given in M. BECQUEREL'S paper, I was struck with 

 the close resemblance between the phosphorogenic spectrum and that tithonographic 

 spectrum on iodide of silver of which Sir J. HERSCHEL has given an elaborate account 

 (Phil. Mag., Feb., 1843). As far as the eye could judge, they seemed perfectly alike ; the 

 tithonographic spectrum in question was obtained by me in Virginia. This coincidence 

 was so striking that it appeared almost certain that the phosphorogenic emanations of 

 BECQUEREL were the same as my tithonic rays: there was the upper spectrum com- 

 mencing at the line G, and going beyond the farthest confines of the violet, exerting a 

 positive action ; there was also the lower spectrum, commencing at the line F and going 

 below the red ray, and exerting a negative action ; a phenomenon absolutely the same 

 as that traced on the Daguerreotype plate. 



976. The phosphorogenic rays that come from the sun have the same place in the 

 spectrum, or are dispersed by the prism exactly in the same way as the tithonic rays. 

 To all appearance these may be expressions for the same agent. 



977. We must remember, however, that the phosphorogenic rays of the sun differ 

 from those of an electric spark. Glass to the former is transparent, to the latter it is not. 



978. Before, therefore, I can carry this argument to the point on which I design it 

 to bear, it is necessary to ascertain the index of refraction of the rays of an electric 

 spark to which glass is impervious. 



979. This I proceeded to determine in the following way : At the distance of six 

 inches from the terminations of two blunt wires, between which the spark from a Ley- 

 den vial was caused to pass, I placed a lens of quartz, the focus of which for parallel 

 rays was six inches, and then intercepted the resulting beam by a diaphragm with a 

 circular aperture in it one third of an inch in diameter. I had caused an equiangular 

 prism of quartz to be cut and polished from a large and perfectly faultless rock-crystal ; 



