OF ARTS AND SCIENCRS. 



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. 



n' = number of eoils in earth inductor. 



R = radius of earth inductor in centimetres. 



K = the intensity of earth's magnetism I ^ about — ^^tt?,!' 



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 M :=z — — — — - (for all 



u n dL 



points except very near the ends). 



Table III. shows the magnetism of magnet Xo. 1, and armature iu 

 terms of K. 



TABLE III. 

 a. The Armature. 



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

 the magnet. 



