OBSERVATIONS OF THE MAGNETIC FORCE. 
267 
§11. Lieut. Lefroy’s Observations of the Magnetic Force. 
These observations were of two kinds ; those which were designed to determine 
the absolute value of the horizontal component of the force ; and those which had for 
their object to determine the ratio of the total force at different stations. For the 
absolute determinations magnets of small dimensions were employed in portable ap- 
paratus, which will be hereafter described. The observations to determine the rela- 
tive values of the total force were made with two needles on Dr. Lloyd’s statical prin- 
ciple, used in Gambey’s circle, and with two needles on Mr. Fox’s principle, used in 
a circle of seven inches diameter. The Lloyd’s needles were distinguished as L. A. 
and L. B. : the Fox’s as F. A. and F. C. Experiments to determine the coefficient in 
the temperature corrections of these needles were made at Toronto in the first three 
months of 1843. The observations at high temperatures were made in the detached 
building of the observatory, which was heated for the purpose by a copper stove : 
those at low temperatures were made partly in the same room and partly in the open 
air outside the building. In Tables X. and XI., in which these experiments are re- 
corded, v denotes the angle of deflection with a constant weight at the temperature t , 
in the experiments at low temperatures ; 6 the inclination ; and <p the total force, 
which is ~ 77 — \ with Dr. Lloyd’s needles, and sin v with Mr. Fox’s ; v ' & and o' 
sm (p — v ) 7 7 r 
denote the corresponding values in the experiments at high temperatures. Then, q 
being the coefficient, (p—f (1 — q ( t—t )) ; and q= zzjy 
Table X. 
Abstract of the Observations made at Toronto to ascertain the value of q for the 
needles L. A. and L. B. 
L. A.. 
Low temperatures. 
High temperatures. 
1842 and 
1843. 
t. 
V . 
e. 
<f. 
1843. 
t’. 
v\ 
6>. 
?'• 
Dec. 10. 
29-0 
-3§ 37*0 
75 17*2 
0-86509 
Jan. 9. 
66-9 
-36 45-9 
75 15-4 
0-86414 
Jan. 13. 
31-8 
-36 41-9 
75 13-9 
0-86433 
13. 
54-4 
-36 33-5 
75 13-9 
0-86506 
13. 
32-0 
—36 34-5 
75 13-9 
0-86497 
17. 
35-0 
-37 17*2 
75 13-4 
0-86123 
17. 
61-8 
-36 36-8 
75 13-4 
0-86472 
30. 
38-0 
-36 38*8 
75 16-5 
0-86487 
30. 
65-4 
-37 02-3 
75 16-5 
0-86284 
Feb. 1. 
25-6 
-36 24*2 
75 15-7 
0-86604 
Feb. 1. 
62-3 
-36 41-1 
75 15-7 
0-86459 
2. 
25-8 
-36 31-7 
75 15-7 
0-86542 
2. 
79-0 
-36 36-8 
75 15-7 
0-86499 
3. 
27-4 
-36 39-5 
75 15-6 
0-86470 
3. 
80-2 
-36 58-7 
75 15-6 
0-86311 
4. 
37-0 
—36 54-9 
75 15*6 
0-86337 
4. 
76-4 
-36 44-6 
75 15-6 
0-86431 
10. 
25-3 
—36 37*0 
75 14-7 
0-86479 
11. 
71-9 
-36 47-6 
75 14-7 
0-86387 
10. 
27-5 
-36 37*0 
75 14-7 
0-86479 
11. 
64-5 
-37 08-3 
75 14-7 
0-86215 
30*4 
-36 41-2 
75 15-2 
0-86451 
68-3 
0-86398 
Hence for L. A. •0000 16. 
