On the Magnetic Iiifluence of the Lunar Spectrum. 43 



needle ought to be placed, in order to expose it to the most 

 refrangible rays of the spectrum. The difficulty was only 

 obviated by bringing the prismatic action to bear upon it, 

 when it was floating upon water ; this had been done previously 

 in regard to the solar spectrum without occasioning any change 

 in the polarity of the needle: its point continued to be its 

 north pole, which might have arisen from the prevalence of ' 

 the reciprocal influence between it and the magnetic meridian 

 of the earth, when it was in that position ; while there was no 

 parallelism between its direction and that of the terrestrial 

 magnetic currents, when it was lying on a table. The great 

 superiority of the magnetic power of the moon, when com- 

 pared with that of the sun, appeared immediately in reference 

 to this fact, because the experiments about to be detailed 

 were commenced iche7i the needle was parallel to the terresti'ial 

 magnetic currents. 



14-. In order to prove that the substance of the prism itself 

 had no magnetic properties or disturbing influence, it was 

 brought close to the floating needle in various positions with- 

 out causing the least motion, when it had adjusted itself in the 

 plane of the magnetic meridian of the earth. 



15. The following observations were then made: — 

 The needle, with its point directed towards the north mag- 

 netic pole of the earth, almost immediately exhibited the ef- 

 fects of the lunar influence; at Jirst its point deflected from 

 the magnetic pole to the true north pole of the earthy and it ar- 

 ranged itself in a direction parallel to that of the true meri- 

 dian. Then the whole needle began to move laterally^ but 

 slowly, towards that part of the spectrum in which the blue 

 and violet raj's predominated. Its point, however, gradually 

 deflected from the true meridian very soon after the com- 

 mencement of this lateral movement, and the needle at last 

 placed itself at right angles to the terrestrial meridian. When 

 it was parallel to the earth's equator, it suddenly acquired a 

 new and contrary impulse, and a comparatively rapid darting 

 motion from east to west in the direction of its length, with 

 its head foremost ; as soon as its head was beyond the spec- 

 trum, it turned towards the north : this produced a new cui*- 

 vilinear movement of the whole needle, which brought it past 

 its original position, when it was parallel to the terrestrial 

 magnetic meridian; and there was a cessation of motion when 

 it again became parallel to the true meridian of the earth, 

 where it remained stationary for a short time although the 

 prism was not moved. It must be borne in mind, that the 

 moon was itself to the east of the meridian during the experi- 



