OBSERVATIONS OF THE MAGNETIC FORCE. 
287 
Report relative to the determinations of Absolute Horizontal Force, drawn up by 
Lieut. I. H. Lefroy, R.A., and transmitted from Canada in 1845. 
“The measurements of the absolute horizontal force, from September 1842 to 
March 1843, were made with a transportable magnetometer by Meyerstein of Got- 
tingen, on the plan of Professor Weber, described in Taylor’s Scientific Memoirs, 
Part VIII. The deflecting bar in this instrument was retained at right angles to the 
meridian, and the angles of deflection were measured upon a long scale carried by 
the telescope. 
“ Two deflecting bars were supplied with the instrument, 0-4 inch in diameter 
and 3*9 and 3'75 inches in length respectively. The angle of deflection was first ob- 
served with the farthest end of the deflecting bar at the distance 1’5 foot on the 
deflection scale ; secondly, with the same end at 1*7 foot ; and finally with the nearer 
end at 1*7 foot, giving the following as the distances of the deflecting bar. The bars 
are distinguished by the letters and numbers marked upon them. 
N. IX. 
N. 13. 
feet. 
feet. 
r = 1-3437 
1-3371 
r' =1-5437 
1-5371 
r"= 1-8562 
1-8629 
“The third distance is as nearly in the ratio of T32 to the first as the graduation 
of the scale admitted. The angular value of one division of the scale was l'*01 1. 
“The following Table contains the weight and dimensions of the magnets and of 
the stirrup in which they were vibrated, together with those of the small cylindrical 
brass weights, numbered 5 and 6, used in determining the moment of inertia of the 
suspended mass. 
Table XXVIII. 
Length. 
Diameter. J Weight. 
Deflecting bar, N. IX 
ft. 
0-3125 
0-3257 
0-1243 
0-1245 
0-3902 
ft. 
0-0325 
0-0354 
0-0342 
0-0342 
grs. 
1024-4 
1092-4 
417- 9 
418- 2 
736-0 
Deflecting bar, N. 13 
Cylindrical weight, No. 5 
Cylindrical weight. No. 6 
Stirrup, between the points of suspension 
“ The moment of inertia was found by vibrating each bar with and without the 
cylindrical weights, and the values of the constant t 2 K given by these experiments at 
various stations are included in the following Table, where 
K'=^(Z 2 -|-r 2 )W=log 1*50454, 
rji-2 
and K =K f ^ 2 _f 2 • 
2 p 2 
