EXPERIMENTS, &c. 



CHAPTER I. 



EXPERIMENTS MADE TO DETERMINE WHETHER LIGHT EXHIBITS ANY MAGNETIC ACTION. 



(From the Journal of the Franklin Institute for February, 1835.) 



CONTENTS : Character of the Sky in Virginia. Examination of Mr. Christies Ex- 

 periment. Needles not affected by the Violet Rays. No Reaction between a Magnet 

 or Voltaic Currents and Light. 



1. " THE more refrangible rays of light are said to possess the property of rendering 

 iron and steel magnetic. The existence of this property was first asserted by Dr. Mo- 

 richini, 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 experiments, sewing needles were rendered magnetic by exposure for 

 two hours to the violet ray, and the magnetic virtue was communicated in still shorter 

 time when the violet rays were concentrated by means of 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. Zan- 

 tedeschi, of Pavia (Bibl. Univ. for May, 1829), but their accuracy has been doubted by 

 Messrs. Riess and Moser, who consider that the means employed by Mrs. Somerville 

 for ascertaining the magnetic state of the needles were not sufficiently exact. They 

 found the oscillation of needles to be wholly unaffected by exposure to the prismatic 

 colours. (Brewsters Journal, ii., p. 225, N. S.) This must still be regarded, therefore, 

 as one of the disputed points in science." (Turner?) 



2. It has been supposed that this disparity of results arose entirely from local circum- 

 stances. A hazy atmosphere, such as is met with in the northern and middle countries 

 of Europe, might perhaps influence, in some manner, this peculiar property of light, when 

 the clearer sky of Italy allowed an opportunity of making the experiment. Some, in> 

 deed, have thought that the observers, who were said to have verified the original re- 

 sults of the Italian philosopher, were themselves deceived in not having previously as- 

 certained the magnetic state of the needles they used. That mistakes of this and a 

 similar kind are easily made, will appear in the course of this communication. 



3. During the past summer, I have attempted to satisfy myself whether the more re- 

 frangible rays really exert any magnetic influence ; and happening to reside in the south 



