Mr. Airy on the 
564 
D = D.R. {(1 +%->-£) cos /- (i + $-$) cos 3 / 
+ (£ e ’-^) cos 5/}. 
I now proceed to compare this theory with observation. 
In selecting from the numerous determinations of the varia- 
tion of gravity one set for our present purpose, there can be 
no hesitation in fixing on Captain Sabine's, as extending 
over the greatest arc of latitude, and as being made by the 
same observer with the same instruments at no great interval 
of time. The following are the places of his observations 
and their latitudes, with the lengths of the seconds’ pendulum 
determined by him. 
Place. 
Latitude. 
Length of seconds’ pen- 
dulum in inches. 
St. Thomas . 
0 1 a 
24 41,2 
39,02074 
Maranham . 
2 31 43,3 
,01214 
Ascension 
7 55 47,8 
,02410 
Sierra Leone . 
8 29 27,9 
,01997 
Trinidad . . 
10 38 56 
,01884 
Bahia . . . 
12 59 21 
,02425 
Jamaica . . 
17 56 7,6 
,03510 
New York . 
40 42 43,2 
,10168 
London . . 
51 31 8,4 
,13929 
Drontheim . 
63 25 54,2 
,174 56 
Hammerfest . 
70 40 5,3 
,19519 
Greenland 
74 32 18,6 
,20335 
Spitzbergen . 
79 49 57,8 
,21469 
