S90 Prof. Draper on the Chemical Action of Light. 



So though all experiments have failed to disturb a ray of light 

 by magnetism, some change may perhaps be brought about by 

 compelling the oscillating particles of the shining body to move 

 in a new path. 



"V^lien Bancolari's experiment on the influence of the poles of 

 a powerful magnet on a flame was first published, I repeated it 

 at once, expecting that the oscillations of the shining particles 

 were constrained to take place in one plane by the magnetism, 

 and that the light emitted should be polarized. The result, 

 however, did not seem to prove this. 



A similar experiment was then made with the electric spark 

 from the prime conductor of a machine. It was compelled to 

 cross between the poles of a powerful electro-magnet. But when 

 the magnetism was on, it could not be proved that the light was 

 polarized. 



M. De la Rive has shown, that the voltaic arc of flame between 

 charcoal points is greatly disturbed when it passes between the 

 poles of a powerful electro-magnet. In the hope that this would 

 produce the expected disturbance, I examined an arc formed 

 between points of copper, platinum, and gas carbon ; but though 

 the sounds emitted were strong, resembling the sudden tearing 

 of a piece of cloth, I failed to prove that the light was polarized. 



In like manner the induction spark from a contact breaker, 

 and the phosphorescent light from fluor spar, were tried without 

 success. 



I still ex:pect, however, that with more powerful means than 

 those here employed the experiment would succeed, and hope it 

 will be attempted by those who have adequate insti-imients at 

 their command. 



At the commencement of this memoir it was stated, that we 

 should discuss, — 1st, the manner in which a ray of light acts in 

 bringing about decomposition, and the changes it midergoes ; 

 2nd, the nature of the impression made on the material group, 

 the decomposition of which ensues. The observations I propose 

 ofl^'ering in relation to the former of these points are completed ; 

 I now pass to some remarks respecting the last. 



An examination of many cases of the decomposition of bodies 

 by light has led me to the ^conclusion, that its cause is to be attri- 

 buted to the inability of the group of molecules affected to with- 

 stand the periodic impulses communicated to them. Of those 

 molecules, some perhaps take on a vibratory movement more 

 readily than the others ; and the continuance of a given group 

 becomes impossible, and a re-arrangement ensues. 



But in other cases, the mechanism of decomposition is un- 

 doubtedly diffc'rent ; a change is impressed in one of the ele- 

 ments acted upon, which weakens its affinity for the others. 



