OBSERVATIONS ON THE MAGNETIC FORCE. CXXXtX 
The results on the 26th of June, and on the 23d and 24th of July, 1810, 
compared with the observations in England, will also be found to agree as well 
with the theory as it is reasonable to expect in experiments, where neither 
time nor circumstances admitted the adoption of the precautions, requisite 
to ensure the utmost accuracy of which they are capable ; and where, perhaps, 
the moving of the ice during the observations may have introduced an addi- 
tional error which no care could guard against. By the experiments of the 
26th of June, the force had diminished by Needle No. 2, as 2.815 to 1, and 
by No. 3 as 2.86 to 1 ; and supposing the Dip to have been 83° 04', as was 
found by rather an indifferent observation, the theory would require a dimi- 
nution of 2.5 to 1. By the experiments of July the force had diminished by 
Needle No. 2, as 3.28 to 1, and by No. 3, as 3.198 to 1 ; the calculated dimi- 
nution being 3.12 to 1. 
A description having been given of the instrument with which the preced- 
ing experiments were made, it may be proper to add, that the mode of 
drawing the Needle from its natural direction by a magnet previous to its 
oscillation, appears objectionable ; and might be avoided by a contrivance to 
retain and release it at any arc at which it might be wished to commence 
the vibrations ; also, that it may be desirable that the silk suspension should 
be longer than nine inches, especially in experiments in high magnetic lati- 
tudes where the force of magnetism is so greatly diminished ; and that great 
attention should be paid to the purity of the brass which may be used in the 
construction of the instrument. 
It may, perhaps, be useful to add a remark, that when the ratio of the 
Variation of the Magnetic Force shall be thoroughly determined by experi- 
ment, the oscillations of an horizontal needle, suspended as above, will become 
a measure of differences in the Dip of the Needle far more accurate in the 
higher latitudes than the Dipping Needle ; and, consequently, the dip being 
confidently known at any one place of Observation, it may be determined at 
others with much greater precision than by the usual method. 
The frequent use which was made of the Dipping Needle having suggested 
