232 Mr. Christie on magnetic 
be greatly increased by placing the needle so nearly in the 
focus of a large lens or reflector, that the rays should be 
concentrated on the space in which the needle vibrated. In 
this case, however, the intensity of the needle might be so 
much diminished by the high temperature, as to render 
doubtful the cause of the effect observed. 
The repeated failures of Morichini’s experiment of mag- 
netising a needle by the violet ray, even under the most 
favourable circumstances, and in the ablest hands, have led 
many to doubt whether the effects, which were in some cases 
observed, were to be attributed to the influence of the ray ; 
but as the experiments which I have detailed indicate mag- 
netic influence in the compound solar rays, and are besides 
easily repeated, they will, I think, tend considerably to remove 
these doubts. 
Royal Military Academy, 
November 15, 1825. 
Additional observations. 
Since the foregoing paper was read, having made some 
further observations which show more decidedly than the 
preceding that the effect which I have described is due to 
magnetic influence in the solar rays, I beg here to add them. 
I was satisfied that the decrease in the terminal arc, when 
the needle vibrated in the sun, could not be due to the in- 
creased temperature of the metallic compass-box in which 
the needle vibrated, since in the experiment which I have 
described, and which I have carefully repeated, the effect 
