370 



Magnetic Influence of Solar Light. 



Expt. I. — Camp, Berheri, Doah Canal, November 20th 1841. 



Experimental needle A, having a length of 1.625 inches 

 and a diameter 0,031, " with brightly polished surface and 

 having no previous magnetism, was exposed upon a sun-dial 

 to the light of the sun passed through a dark green glass, 

 from 10 a. m. to 12, and on being submitted to the action of 

 the testing needle, the following results were observed. 



1. On approximating the north pole of the testing needle 

 to the extremity of the exposed part of needle A, the latter 

 was strongly attracted. 



2. On repeating this process with the extremity of the 

 covered part of A, equally strong repulsion was manifested. 



3. On approaching the south pole of the testing needle to 

 the extremity of the exposed part of A, repulsion, equal to the 

 attraction exhibited in the first observation, was displayed. 



4. On repeating the approximation to the covered part a 

 corresponding attraction was observed. 



Whence it clearly appears that the experimental needle 

 A had become perceptibly magnetic, its exposed end hav- 

 ing acquired southern, its covered end northern Polarity ; 

 the enquiry immediately arises, was this effect clearly and 

 distinctly due to the action of solar light ? I shall therefore 

 now state the circumstances that appear to me both to ren- 

 der this more than doubtful, and to indicate one of the 

 sources of error to which the method of observation employ- 

 ed, is exposed. The needle A, while subjected to the 

 action of the sun's light, was fixed by means of a slender 

 wooden support in the place of the magnetic meridian, 

 forming an angle with the horizon of between 40° and 50°. 

 It was therefore in a most favourable position for being 

 magnetised by the inductive action of the earth : suppos- 

 ing it had been so, in how far, it may be enquired, do 

 the indications of Polarity actually obtained correspond 

 with those that theoretically would result from such action. 



