330 Mrs Soinerville on the Magnetizing Power 



It also attracted and suspended a fringe of iron filings. The 

 extremity of the needle that was exposed to the action of the 

 violet rays, repelled the north pole of a compass needle. This 

 effect was so distinctly marked, as to leave no doubt in the 

 minds of any who were present, that the needle had received 

 its magnetism from the action of the violet rays. 1 ' 



Such was the state of this subject when Mrs Somerville di- 

 rected to it her attention; and it is no slight praise to say, that 

 she has set to rest a question on which the scientific world was 

 divided, and that by the sagacity and ingenuity with which she 

 has conducted her experiments, she has rendered visible, even 

 in our northern climate, one of the most delicate of the mag- 

 netic influences, which, it was agreed on all hands, required 

 for its developement the serene sky of an Italian climate. 



The following is a general outline of these interesting ex- 

 periments. 



Having obtained the prismatic spectrum by means of an 

 equiangular prism of flint glass placed in a hole in the window- 

 shutter, Mrs Somerville took a sewing needle, about an inch 

 long, and entirely devoid of magnetism. * Conceiving that 

 no polarity would be superinduced if the whole needle were 

 exposed to its action, she covered one half of it with paper, 

 and exposed the other half to the violet rays of the spectrum 

 cast upon a pannel at the distance of five feet. In about two 

 hours, the needle had acquired magnetism, the exposed end ex- 

 hibiting north polarity. This experiment was often repeated, 

 and always with the same result. 



By a similar process, Mrs Somerville ascertained that the 

 indigo rays had nearly as great an effect as the violet, and 

 that the blue and green rays likewise produced the same ef- 

 fect, though in a less degree. 



Mrs Somerville next tried the yellow, orange, and red rays, 

 but neither in them nor in the calorific rays, was the slightest 

 effect produced, even when the experiments were continued 

 for three successive days. 



* This was ascertained by its attracting indifferently either pole of a 

 sewing needle magnetised in the usual way. This magnetised needle was 

 pushed through a piece of cork, in which was inserted a glass cap, and it 

 was in that state made to revolve freely on the point of another sewing 

 needle. 



