t 52 ] 



IX. On the Polarization of the Chemical Rays of Light. 

 By John Sutherland, M.D., Liverpool*. 



IT has been long known that the invisible rays of the solar 

 light, which manifest their presence by inducing chemical 

 action, are possessed of some of the properties of the luminous 

 rays. Their capability of being reflected and refracted must 

 have been observed at the time of their discovery ; and Dr. 

 Thomas Young proved that they were capable of producing 

 the phaenomena of interference, by allowing the rays beyond 

 the violet extremity of the spectrum to fall on paper covered 

 with chloride of silver, after having been transmitted through 

 glasses showing Newton's rings. The same phenomenon was 

 also exhibited directly by M. Arago,who made use of Fresnel's 

 experiment for the purpose of demonstrating it. 



On the 21st December 1812, M. J. E. Berard read a paper 

 before the French Institute, "Sur les proprietes des differentes 

 especes de rayons qu'on peut separer au moyen du prisme de 

 la lumiere solaire," which was published in the " Memoires 

 d'Arcueil," vol. iii. ; and in this memoir, after investigating se- 

 veral properties of the chemical rays, he relates the following 

 experiment: — " I received the chemical rays directed into the 

 plane of the meridian, on an unsilvered glass, under an inci- 

 dence of 35° 6 f . The rays reflected by the first glass were 

 received upon a second under the same incidence. I found 

 that when this was turned towards the south, the muriate of 

 silver exposed to the invisible rays, which it reflected, was 

 darkened in less than half an hour; whereas, when it was 

 turned towards the west, the muriate of silver exposed in the 

 place where the rays ought to have been reflected, was not 

 darkened, although it was left exposed for two hours." From 

 this experiment he deduces that the chemical rays can be po- 

 larized like white light, when they are reflected by surfaces of 

 glass under a certain angle, and that this angle appears to be 

 very nearly the same for the two kinds of rays. " It is," he 

 says, " consequently to be presumed that the chemical rays can 

 undergo double refraction in traversing certain diaphanous 

 bodies, and, lastly, we may say that they enjoy the same phy- 

 sical properties as light in general." 



An experiment similar to M. Berard's will be found de- 

 tailed in the following paper, although I was not aware of there 

 being any such on record, till informed of it by the kindness 



* Communicated by the Author ; having been read before the Royal So- 

 ciety of Edinburgh, December 21, 1840: a communication on the same 

 subject had been previously made to the Literary and Philosophical Society 

 of Liverpool, November 2, 1840. 



