66 Variation of the Magnetic Needle. 



riation deduced by the usual rules of spherical trigonometry, 

 The observations were as follows. 



1805, Nov. ISd.dh. 15' A. M. 4 obs. 5° 58' 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 

 four inches in length, suspended on an agate. The places 

 where the instrument was fixed, and method of observing, 

 were exactly similar to those before mentioned. 



Mean of 112 obs. 5 20 W. 



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 

 place of observation in 1805, the variation was observed as 

 above by both theodolites, the results are — 



