1826.J Royal Society. 22& 



4he yiolet ray of the solar spectrum ; the experiment was 

 repeated, without success, by rrof. Configliachi at Pavia, and 

 M. Berard, at Montpellier ; Dr. Brewster states, in his Treatise 

 on New Philosophical Instruments, that Sir H. Davy and the 

 late Prof. PJayfair witnessed a successful repetition of it in 

 Italy ; but from the indistinct and contradictory results that had 

 been obtained even in .that country, it had been concluded that 

 the experiment was still more unlikely to succeed in our own 

 northern climate, and no further elucidation of the subject had 

 been obtained. 



The unusual clearness of the weather, however, last summer, 

 had induced Mrs. S. to institute some experiments on the sub- 

 ject ; which she next proceeds to detail. 



An equiangular prism of flint-glass being placed in an aperture 

 in a window-shutter, a sewing needle, about an inch long, which 

 had been previously ascertained to be devoid of magnetism by 

 its attracting indifferently either pole of a magnetized needle,* 

 was exposed to the violet ray of the spectrum, thrown on a 

 Dannel, at the distance of about five feet. One half of the needle 

 was covered with paper, as the author did not deem it likely 

 that polarity would ensue from the action of the light, if the 

 whole of the needle were uniformly exposed to its influence. In 

 about two hours, the needle became magnetized, the exposed 

 end being found to be the north pole. The experiment having 

 been many times repeated with the violet ray, and always with 

 success, the blue and green rays of the spectrum were next 

 ascertained to produce a similar effect, but in a less degree, and 

 the indigo ray in a degree nearly as great as the violet. The 

 yellow, orange, and red rays had no effect whatever on the nee- 

 dles exposed to them, even when the experiments were conti- 

 nued for three successive days ; nor was any magnetism deve- 

 loped by the calorific rays, which showed that heat had no share 

 in causing the results. 



Pieces of clock and watch-springs, about an inch and a half 

 long, and from an eighth to a quarter of an inch in width, pre- 

 viously ascertained to be unmagnetic, or reduced to that state 

 by heating them, were exposed m the same manner to the more 

 refrangible rays, and they also were rendered magnetic, the 

 exposed ends always becoming north poles. They appeared 

 indeed to be more susceptible of magnetization than the needles, 

 probably on account of their greater extent of surface and blue 

 colour. Bodkins were not affected, owing, perhaps, to their 

 greater mass. When the violet ray was concentrated by means 

 of the large lens employed by Dr. WoUaston in his experiments 



• The magnetic needle employed for this purpose was also a sewing needle, wliicli, 

 after it had been magnetized in the usual way, was driven through a cork in which a 

 glass cap was inserted; and it was then suspended, so as to revolve freely, on the 

 2>oint of another sewing needle. 



New Series, vol.. xi. q 



