418 PROCEEDINGS OF THE AMERICAN ACADEMY 



Hence 



tau I 



87.16 



which gives 



22.(56 

 i = 75* 25' 30". 



Measurements of March 20, 1878. 



(«) Determination of Mil. 



To find t, 8 measurements were made, with the following results ; 



was found equal to .01979 ; 



and these values give 



MII= 3005600. 



((3) Determination of 



M 

 H' 



I here used a very light magnet, consisting merely of three pieces 

 of magnetized watchspring. A mirror and a piece of aluminum foil to 

 stop the vibrations were used. It was suspended by a single fibre of 

 silk about 400 mms. long. The tor.-^ion of this thread was impercep- 

 tible even on turning the upper circle through an angle of 360^. 



Six complete measurements were made, with the following results. 



The distance of the scale from the mirror was 151 G mms. 



