168 Mrs. Somerville on the magnetizing Power 



outside, could measure both columns before it had time to 

 change its temperature ; but the other is surely sufficiently ac- 

 curate. 



Experiments of this kind, I intended to have made during 

 the cold weather, but did not get them attended to, and the 

 season is now too far advanced for conveniently obtaining the 

 requisite temperatures. 



The expansions of the columns or the difference in their 

 lengths, may be increased or rendered more sensible by 

 lengthening the tubes. But care must be taken to keep each 

 bath at the same temperature throughout its whole depth. 

 By placing a pretty wide tube open at both ends upright in 

 the bath, and moving a solid piston in it, the temperature may 

 be easily rendered uniform from top to bottom. Indeed, the 

 motion of a piston alone, without a tube, would probably be 

 sufficient. 



The method proposed by Mr. Oswald Sym*, though quoted 

 with approbation by Dr. Thomson f, is entirely a deception. 

 It can at best give the temperature answering to the apparent 

 greatest density of water in glass ; just as if the water were in 

 a bottle, and its height measured in the neck. 



April 15, 1826. HENRY MeIKLE. 



XXIV. On the magnetizing Power of the more refrangible Solar 

 Rays. By Mrs. M. Somerville J. 



T N the year 1813, Professor Morichini, of Rome, discovered 

 ■*- that steel exposed to the violet rays of the ' solar spectrum 

 becomes magnetic. His experiments were repeated by Pro- 

 fessor Configliachi, at Pavia, and also by Mons. Berard, at 

 Montpellier, without success. I am not aware of any one 

 having attempted them in this country, perhaps from the be- 

 lief that experiments which had sometimes failed in Italy, were 

 not likely to succeed in our more northern climate. The un- 

 usual clearness of the weather last summer, however, induced 

 me to try what could be accomplished in this country. Ac- 

 cordingly, in the month of July, an equiangular prism of 

 flint glass, the three sides of which were each 1*4 by 1*1 inch, 

 was fixed in a slit made to receive it in a window-shutter: 

 by this prism a coloured spectrum was thrown on an oppo- 

 site panel, at the distance of about five feet. I used for the 

 subject of experiment a very slender sewing-needle an inch 



* Annals of Philosophy, vol. ix. page 387. 

 f System of Chemistry, 6th edition, vol. i. page 43. 

 j From the Philosophical Transactions for 1826, Part I. This paper 

 was communicated to the Royal Society, Feb. 2, 1826. 



long, 



