66 Variation of the Magnetic Needle. 
riation deduced by the usual rules of spherical trigonometry. 
The observations were as follows. 
1805, Nov. 18d. 9h. 15’ A, 4 obs. 5° 58’ W. 
é Gy 47 
4 P. M. 5 
19:9 A. M. 6 6 02 
2 P. M. 6 5 56 
22:2 P. M. 10 6 15 
P3 9 A. M. 9 5 56 
2: 4002. M. 6 5 45 
26 2 P. M. 10 5 51 
2i: <8 A. M. 12 5 42 
eee P.M. 10 6 Ol 
28...9 A. M. 10 5 43 
3 P. M. 12 6 06 
23; 9 A. M. 3 5 50 
30. 9 A. M. 12 6 Oj 
Mean of 115 obs. 5 57 W. 
In the year 1808 at a house in Summer Street about an 
eighth of a mile south of the place where the above obser- 
vations were made, I observed the variation with another, 
more highly finished theodolite furnished with a needle of 
1808, June 27d. 7h. 1' A. M. 12obs. 5° 11'W. 
45 P.M. 20 
5» 22 
28 6 26 A. M. 20 5 25 
29 6 44 A: M. 20 5 08 
6.32 Pow. 20 5 26 
> July: Bo: 7 + 30 AME: ---20 & °25 
Mean of 112 obs. 5 20W. 
In the year 1810, at a house in the northern part of Mar- 
ket Street, Salem, about a quarter of a mile east of the 
ce of observation in 1805, the variation was observed as 
above by both theodolites, the results are— 
