amount of the dip of the magnetic needle , in London , &c. 17 
according as the differences of the sines progressively diminish; 
so in this method, on the contrary, the influence of such errors 
will be lessened in the same ratio : thus in dips of 65° and 
upwards, the determination may be made with very consi- 
derable accuracy, with instruments generally of good con- 
struction, and with needles of which the terminations of the 
axis are very slender. 
The horizontal vibrations should be made under a cover 
of glass, or of wood with glass windows ; the silk suspension 
should be several inches in length, and perfectly free from 
twist. 
The following experiment was made with the needle num- 
bered 3 in the preceding; the silk line was 15 inches in length, 
and was fastened in a groove near the end of the axis; the 
oscillations 
were 
made in 
arcs under 
25 0 . 
Oscil. 
Times. 
Oscil. 
Times. 
m 
S 
70th 
m s 
m s 
O 
O 
OO 
7 2 5,75 * 
'7 25,75' 
2nd 
O 
13 
72d 
7 3 8 >5 
c 
7 25,5 
4th 
0 
25,75 
74th 
7 51,25 
'o < 
CO 
O 
7 25,5 > 
6th 
0 
38,5 
76th 
8 04 
r 
7 2 5,5 
8th 
O 
51,25 
78th 
8 16,75 
O 
7 2 5,5 
10th 
1 
04 
■* 80th 
8 29,25 J 
L7 25 , 25 J 
ms s 
Here making 7 25,5 = 445,5 = H, and M as before 
= 260,25, = '341265 cosine of 70° 02 ,6 N. dip. 
The results by the three different methods collected in one 
view, are as follow, viz : 
By 10 experiments with Meyer’s needle - 70,02,9 
By the times of oscillation in the magnetic meridian 
and in the plane perpendicular to it; mean by [70,04 
three needles. J 
By the times of vertical and horizontal oscillation 70,02,6 
mdcccxxii. D 
