amount of the dip of the magnetic needle , in London, &c. 9 
Experiment 1. August 3d, 1821, with sphere No. 8, midway 
between the edge of the needle and the end of the screw. 
In this experiment all the arcs were on the north side of 
the vertical, and were therefore all read positively. 
Face A of the Needle towards Face B towards the 
the Observer. Observer. 
0 ✓ 
fN. end 31 00 
O / 
S. end 30 52 
O / 
N. end 9 18 
S. end 
0 ✓ 
9 18 
31 00 
30 52 
9 1 7 
9 15 
Face of the Circle East < 
31 00 
31 02 
30 52 
3 ° 55 
9 20 
9 24 
9 !9 
9 22 
! 
31 00 
30 52 
9 24 
9 23 
L 
31 02 
30 56 
9 1 9 
9 18 
r 
3 1 25 
31 20 
9 25 
9 3 ° 
31 20 
3 1 13 
9 25 
9 30 
Face West ■< 
31 20 
3 1 22 
3 i »3 
3 1 15 
9 22 
9 21 
9 22 
9 22 
3 1 24 
3 i *7 
9 25 
9 3 ° 
31 26 
31 20 
9 2 S 
9 3 ° 
31 11,7 
31 04,8 
9 22,1 
9 22,4 
31 08,2 = F 
9 22,3 
=/■ 
Poles Inverted. 
0 / 
O ✓ 
O / 
0 / 
I 
30 *5 
O 
O 
5 20 
5 23 
30 12 
30 00 
5 17 
5 20 
Face West 
30 10 
30 00 
5 20 
5 23 
30 10 
30 00 
5 22 
5 26 
1 
l 
30 10 
30 00 
5 22 
5 27 
30 16 
30 04 
5 18 
5 22 
r 
29 20 
29 10 
7 15 
7 10 
1 
29 2 1 
29 1 1 
7 12 
7 12 
Face East ^ 
29 21 
29 12 
7 13 
7 15 
1 
29 l 9 
29 08 
7 13 
7 14 
1 
29 24 
29 17 
7 14 
7 H 
l 
29 19 
29 08 
7 14 
7 14 
29 46,4 
29 36,3 
6 16,6 
6 18,3 
29 
4 - 
II 
O 
6 
17,4 = 
g 
Here tan F = tan 31 08,2 
= 0,6041 1 ; 
O / 
and tan G = tan 29 41,3 = c 
,57012 
tan /— tan 9 22,3=0,16504; tan g = tan 6 17,4 = 0,11022 
tan F + tan/ - = A = 0,76915 ; tanG + tan g = C = 0,68034 
tan F — tan f = B = 0,43907 ; tanG-— tan g = D = 0,4599 
B + D = 0,89897 
c 
MDCCCXXII. 
