( 76 ) 
be no more than what is neceftary to prevent the 
Card from being too much affe&ed by the Motion 
of the Ship. Some Obfervations incline me to think, 
that a Sea-Card Ihould not exceed fix Inches Diame- 
ter, and that mod of thofe generally ufed, are too 
heavy for nice Experiments, tho’ they may be well 
enough adapted for common Purpofes. 
In the Months of March and slpril, 173 z, the 
Variation at Black’ River in Jamaica , was very ac- 
curately obferved to be from 6° to 6 0 oj' Eafterly. 
Off the Havanna about 4 i Deg. Eafterly. 
The reft of the Obfervations I made, are exprelfed 
in the following Table. 
Latitude. 
N. 
Lo-ngit. 
from Lon- 
don, W. 
Variat. 
Latitude. 
Longit. 
from Lon- 
don, W. 
Variat. 
Deg.Min. 
Deg.Min. 
Deg. 
Deg.Min 
Deg.Min. 
Deg. 
27 00 
28 45 
31 00 
32 15 
80 OO 
80 OO 
77 45 
72 30 
1 
4 E. 
3 2 
T A 
1 4 
OO 
35 55 
38 06 
39 10 
39 40 
65 3 ° 
60 30 
57 3 ° 
56 30 
5 w. 
6 3 
8 d 
8 i 
32 40 
32 45 
32 52 
'34 30 
*72 00 
71 30 
70 40 
67 25 
I w. 
ii * 
2 * 
4 -f 
43 OO 
43 05 
44 40 
47 20 
45 00 
44 35 
35 15 
20 20 
9 * 
94 
11 r 
II 
The Inftrumentl ufed was foeafily managed, that 
unlefs the Sea was pretty rough, an Obfervation might 
he depended upon to about a quarter ot a Degree, 
had the Card performed to the fame Exa&nefs. But 
by comparing federal Obfervations made under the 
