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XXIV. On the Diurnal Deviations of the Horizontal Needle 
when under the influence of Magnets . By Samuel Hunter 
Christie, Esq. M. A. Fellow of the Cambridge Philosophical 
Society : of the Royal Military Academy. Communicated by 
Sir Humphry Davy, Bart. Pres. R. S. 
Read June 19, 1823. 
Hav 1 n g been for a considerable time engaged in investi- 
gating different magnetical phaenomena, a suggestion of Mr. 
Barlow’s, that the daily variation of the needle might be 
rendered more sensible by diminishing the directive force by 
means of a magnet, was received by me with much interest. 
He stated to me, that he proposed so to reduce the terrestrial 
force, that instead of the daily variation being only ten or 
twelve minutes, it should amount to three or four degrees, 
or more if necessary. In consequence of this I offered to 
make simultaneous observations, simply for the purpose of 
comparison ; but having been led to prosecute the inquiry 
farther than I at first intended, I think that the observations 
which I have made, with much care, may not be deemed 
unworthy the attention of the Royal Society. 
In making these observations, I adopted an arrangement 
different from that which Mr. Barlow informed me he pro- 
posed making use of. Instead of one magnet applied towards 
the end of the needle, and in the same horizontal plane with 
it, it appeared to me that a more equable distribution of the 
forces acting on the needle would be obtained, if I substituted 
