420 



PROCEEDINGS OF THE AMERICAN ACADEMY 



From A we get, then, 



tan t := 



11.33 

 44' 



From B we get 



tan I = 



22 



86.42 



t = 75° 33' 22". 



{ = 75° 43' 3". 



The mean of tliese two values gives 



t = 75° 38' 12^". 



As our result, we have, then, for the force of magnetism on the 

 20th of March, 



JI= l.G/)G mms. mgms. 

 and 



t = 75^ 38' 12^". 

 And since 



V= If tan I, 

 we get 



V=z 6.4173. 



Note. — To ascertain, at least approximately, the degree of correct- 

 ness attained in this result, I computed the probable mean errors of 

 the time of oscillation in the last determination. The table explains 

 itself. 



