MEMOIR XII.] THE MAGNETIC EFFECTS OF LIGHT. 



MEMOIR XII. 



EXPERIMENTS TO DETERMINE WHETHER LIGHT PRODUCES 

 ANY MAGNETIC EFFECTS. 



From the Journal of the Franklin Institute, Feb., 1835. 



CONTENTS: Mrs. Somerville 1 s experiments. Christie" 1 's experiment. 

 Their results cannot be substantiated. The violet ray has no effect. 

 Blue glasses and blue ribbons also ineffective. 



" THE more refrangible rays of light are said to pos- 

 sess the property of rendering iron and steel magnetic. 

 The existence of this property was first asserted by Dr. 

 Morichini of Rome. Other observers subsequently failed 

 in obtaining the same results, but in the year 1825 the 

 fact appeared to be decisively established by the learned 

 and accomplished Mrs. Somerville in an Essay published 

 in the Transactions of the Royal Society. In her experi- 

 ments sewing-needles were rendered magnetic by expos- 

 ure for two hours to the violet ray, and the magnetic 

 virtue was communicated in still shorter time when the 

 violet rays were concentrated by a lens. The indigo 

 rays were found to possess a magnetizing power almost 

 to the same extent as the violet; and it was observed, 

 though in a less degree, in the blue and green rays. It 

 is wanting in the yellow, orange, and red. Needles were 

 likewise rendered magnetic by the sun's rays transmitted 

 through green and blue glass. These results have been 

 verified by M. Zantedeschi, of Pavia (Bill. Univ., May, 

 1829), but their accuracy has been doubted by Riess 

 and Moser, who consider that the means employed by 

 Mrs. Somerville for ascertaining the magnetic state of 



