OF ARTS AND SCIENCES. 



297 



Table III. gives the magnetism of magnet No. 1 reduced to absolute 

 measure by the following formula : — 



Let n = number of coils in helix. 



?i' = number of coils in earth inductor. 



a = radius of earth inductor in centimetres. 



K = the intensity of earth's magnetism (= about • — Wb)' 



A =. deflection of galvanometer by helix. 

 £ = deflection of galvanometer by earth inductor. 

 dL = the distance over which the helix was slipped. 

 M = the surface magnetism of the bar at the point to be meas- 

 ured, the unit being that quantity which will produce 



unit field at unit distance, then Jf = — — 



B n 



points except very near the ends). 





(for all 



Table III. shows the magnetism of magnet No. 1, and armature in 

 terms of K. 



TABLE III. 

 a. The Armatdre. 



* That is the distribution of the permanent magnetism of the armature upon 

 the magnet. 



