Mr Christie on Magnetic Influence in the Sola?' Rays* 105 



periments, which led me to think, that the compound solar 

 rays possessed magnetic influence, although it had not pre- 

 viously been observed. As this influence is indicated by the 

 arc of vibration of a magnetised needle being more rapidly di- 

 minished when exposed to the sun than when in the shade ; 

 these experiments are easily repeated ; I therefore, in the con- 

 clusion of my paper, ventured to state my opinion that these 

 experiments would tend considerably to remove the doubts 

 which, in consequence of repeated failures, had been enter- 

 tained respecting the magnetic influence of the violet ray in 

 Morichini's experiment. As my paper was read a few meet- 

 ings before that of Mrs Somerville, it was highly gratifying to 

 me to learn, that this opinion in favour of the results obtained 

 by Morichini, was fully confirmed by the brilliant success 

 with which her method of making the experiment had been 

 crowned. 



In making some additional observations in the spring of the 

 present year, with an apparatus, iri constructing which I had 

 scrupulously excluded metal, an account of which is subjoined 

 to the paper ; I first noticed the singular fact, that, when a 

 needle of copper or of glass, and I doubt not, of other sub- 

 stances, is vibrated by the force of torsion, the arc of vibra- 

 tion is also more rapidly diminished in the sun than in the 

 shade ; the effect, however, of the sun's rays being consider- 

 ably greater on a magnetised needle than on the others. The 

 copper, glass, and magnetised needles which I in this case 

 made use of, were not all of the same weight, and the times 

 of vibration were somewhat different ; but supposing the ef- 

 fects proportional to the times, the terminal excess, (that is, 

 the excess of the terminal arc in the shade above that in the 

 sun, after the same number of vibrations commencing from 

 the same point in each case,) would be, for the magnetised 

 needle 13*.75 ; for the copper needle 5°.24 ; and for the glass 

 needle 4°.71 , showing a very decided difference in the effect of 

 the sun's rays upon the magnetised needle. I afterwards, dur- 

 ing the very hot weather of last summer, repeated these expe- 

 riments with needles of magnetised steel, of unmagnetised steel, 



highly important conclusions. Mr Christie's memoir will appear in the 

 Philosophical Transactions for 1826.— Ed. 



