58 On the Polarization of the Chemical Rays of Light. 



effects of varying intensity, two sets of experiments were car- 

 ried on at the same time. A piece of thin window glass was 

 chosen, out of which sixteen plates, one and a half inch long 

 and one inch broad, were cut. These were arranged diago- 

 nally in four bundles, and placed in two tubes; two of the 

 bundles having their planes coincident in one tube, and the 

 other two with their planes at right angles in the other tube. 

 The tubes were placed close to each other in a perpendicular 

 position in the open air, so that the light from the sky could 

 pass directly through them upon two pieces of photogenic 

 paper, cut from the same sheet, and placed so as to receive 

 the chemical emanations. In this position they were left for 

 two hours in a tolerably clear day ; and although the chemical 

 rays had to pass through the same number of plates in both 

 instances, the impressions received by the paper differed much 

 in intensity, that under the tube containing the two bundles 

 with the planes at right angles being much less affected than 

 the other. The explanation of this phasnomenon is that all 

 those chemical emanations which were polarized by the re- 

 peated refraction of the first bundle of glass plates did not 

 pass through the second bundle when their planes were at right 

 angles, and consequently produced no effect on the paper; 

 but, on the contrary, they passed readily through the second 

 bundle, when its plane coincided with that of the first, and 

 produced their characteristic darkening effect. The phae- 

 nomena are in fact similar to those observed with the lumi- 

 nous rays under the same circumstances. 



Such, then, are the results at which I have as yet arrived 

 in this interesting branch of physical research, and they ap- 

 pear to prove that the third great division of the solar ema- 

 nations, like the luminous and calorific, are capable of being 

 acted upon by polarizing forces, and that thus they are all 

 subject to the same beautiful laws. 



Before concluding this communication I may slate, that 

 the photogenic paper employed in the experiments was pre- 

 pared in the usual way with chloride of silver, but that it 

 would be more satisfactory to use small Daguerreotype plates, 

 particularly in obtaining impressions of organized or crystal- 

 line structures by the solar microscope. To effect this, a pair 

 of short polarizing prisms, made according to Mr. Nicol's 

 improved plan, may be adapted to the microscope, one being 

 placed so as to polarize the sun's light before it falls on the 

 object, and the other to analyze the beam immediately after 

 it has passed the object-glass. A sensitive surface placed so 

 as to receive the image thus formed would take a correspond- 

 ing impression of the structure. 



