Pi-of. Draper uu the Chemical Action uf Light. 389 



should be the case ; and the fact is only to be explained on the 



priiijci|)les oiinte^ference .hpf.e d\velt upon,, , , 



■^loni v> 1 101*08 \biB8 81 ti ,sn[1> I noid-w \i i\v ■^'^' 



The next point of inquiry is — 



3rd. In ichat manne)' is the decompodtion of a compound body 

 affected by the condition of polarization of the disturbing ray ? 



A beam of light passing through a circular apertvu-e, one inch 

 in diameter, into a dark room, was received on the achromatic 

 lens of a camera-obseura, and then fell on a doubly refracting 

 prism, so placed as to give on the ground glass two cii-cnlar 

 images of the aperture, ^rd of an inch in diameter, and overlap- 

 ping each other to a small extent. In these images the light 

 %vas of course polarized at right angles respectively. 



When a paper rendered sensitive by being washed with per- 

 oxalate of iron was placed so as to receive them, the light per- 

 mitted to act nine minutes, and its eflfect subsequently brought 

 out by chloride of gold, both images were found of equal black- 

 ness, and the lenticular space formed by their overlapping of 

 greater depth. 



This was repeated with several different compounds, and always 

 with the same result. It shows that plane-polarized light acts 

 precisely like common light, and with a rapidity proportional to 

 its intensity. 



Next, a disc of quartz was placed immediately behind the 

 double refracting spar, so as to give two images of circularly- 

 polarized light on the sensitive surface, but the result came out 

 as in the preceding cases. It does not therefore appear that the 

 direction of the vibrating motion of a ray exerts any action on 

 the decomposition. WTiether it be in all directions, as in common 

 light, or in one as in plane-polarized, or circular, the result is 

 the same. 



Whilst thus attempting to detect a difference in the decom- 

 posing action of common and polarized light, I made some in- 

 quiries as to the ])Ossibility of polarizing light by a magnet. 

 Some of these may here be introduced. 



A great many experiments have been made at different times 

 for the pui-pose 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 intcrcejjt the ray in its 

 course, and submit it to the magnetic action ; but the principle 

 on which my attempts have been founded has been to attack it 

 at its origin, and attempt to produce an impression on the shi- 

 ning body. These methods are essentially distinct. There would 

 be a difference in trying to modify a sound on its passage through 

 the air, and by exerting some influence on the sounding body. 



