106 Mr Christie on Magnetic Influence in the Solar Rays. 



of copper, and of glass of precisely the same weight, the last three 

 having been made to vibrate, by the force of torsion, in as nearly 

 as possible the same time as the first, by the force of terrestrial 

 magnetism. From these I obtained the terminal excess for 

 the magnetised steel needle 11J°; for the unmagnetised steel 

 needle 7^°; for the glass needle 6£ ; and for the copper 

 needle 5°. The excess of the temperature in the sun above 

 that in the shade, varied somewhat in the four cases, being in 

 the first 63°, in the second 73°, in the third 58°, and in the 

 fourth 62° ; and it is probable, that the effects might be slight- 

 ly modified by this circumstance ; but that the excess of the 

 temperature in which the needle vibrated when exposed to the 

 sun, above that when it was screened, was not the cause of the 

 terminal excess with the magnetised needle, among other cir- 

 cumstances, appeared from this, that the terminal arc was con- 

 siderably less; when the needle vibrated exposed to the sun, 

 than when screened by blue glass from its concentrated rays, 

 although the temperature in which it vibrated was some de- 

 grees higher in the latter case than in the former. To what- 

 ever cause we are to attribute the singular fact, that any needle 

 will come sooner to rest when vibrated exposed to the sun 

 than when screened, the great increase which is observed in 

 the effect when a magnetised needle is made use of, proves, I 

 think, decidedly, that the compound solar rays possess a very 

 sensible magnetic influence. 



I have given you this short sketch of some of the observa- 

 tions which I have made since my paper was read, as I consi- 

 dered that you might feel a particular interest in this subject ; 

 and when you have leisure, I shall be happy to have your 

 opinion, or any conjectures you may form as to the nature of 

 the influence, the effects of which I have observed. I am, 

 Dear Sir, yours very truly, 



S. H. Christie. 

 Royal Military Academy, 



4ith November 1826. 



