MEMOIR XXX.] ON BURNING GLASSES AND MIRRORS. 455 



3. In loliat manner is tlw decomposition of a compound 

 body affected by tlie condition of POLARIZATION of the dis- 

 turbing ray ? 



A beam of light passing through a circular aperture 

 one inch in diameter was received on the achromatic 

 lens of a camera-obscura, and then fell on a doubly re- 

 fracting prism, so placed as to give on the ground glass 

 two circular images of the aperture, one third of an inch 

 in diameter, and overlapping each other to a small ex- 

 tent. In these images the light was, of course, polarized 

 at right angles respectively. 



When paper rendered sensitive by being washed with 

 ferric oxalate was placed so as to receive them the 

 light permitted to act nine minutes, and its effect devel- 

 oped by chloride of gold the images (Fig. 100) were 

 found of equal blackness, and the lenticular space formed 

 by their overlapping of greater depth. This was repeat- 

 ed with several different photographic compounds, and 

 ahvays with the same result. It shows that plane polar- 

 ized light acts precisely like common light, and with a 

 rapidity proportional to its intensity, 



In Fig. 100, #, #, the disks of plane polarized light, po- 

 larized at right angles to each other; 

 at <?, the place of overlapping. 



While thus attempting to detect a 

 difference in the decomposing action 

 of common and polarized light, I made 

 some inquiries as to the possibility of polarizing light by 

 a magnet. 



A great many experiments have been made at differ- 

 ent times for the purpose of producing disturbance on a 

 ray of light by magnets. There are two methods which 

 may be resorted to. The one hitherto followed has been 

 to intercept the ray in its course, and submit it to mag- 

 netic action ; but the principle on which my attempts 



100. 



