1877.] and Induction-coefficients of Magnets, 221 



Class E. Deflectors. 





0-000197 



+ 0-000044 



0-000254 



0-000111 



Class E. Deflectors (between temperatures 10° and 60° E.). 



f 



0-000161 



+ 0/000054 



0-000323 



0-000091 



Class E. Various magnets. 





0-000418 



; 



0-000762 



0-000193 



i 



0-00000157 





0-00000398 



0-00000020 



Induction-coefficients. 



The induction-coefficient is determined from observations of deflec- 

 tion made after the well-known method of Lamont, the magnet being 

 alternately placed with its north pole upwards and downwards, but at 

 the same distance from a suspended needle, the difference in the amount 

 of deflection of the latter in the two positions determining the effect of 

 the earth's inductive action upon the magnet. 



The formula, differing slightly from Lamont's, employed in the reduc- 

 tion, and of which the following is a demonstration, is due to the late 

 Mr. John Welsh, E.K.S. :— 



(1) It is assumed that the induction produced by the inducing action 

 of the earth's magnetic force is distributed in the same manner throughout 

 the bar experimented upon as its permanent magnetism. 



Let fx—the increase of the moment of the magnetic bar produced by 

 the action of an inducing force = unity. 

 M=the magnetic moment of the permanent magnetism of the bar. 

 X= horizontal component of the earth's force. 

 Y= vertical component of the earth's force. 

 0=angle of deflection, north end of bar downwards. 



angle of deflection, north end of bar upwards. 

 u— angle of deflection when the bar is used as an ordinary deflector 



at 1 foot distance. 

 i== magnetic dip. 



(2) If c be a constant, and m the magnetic moment of the suspended 

 needle, dm may be taken to represent the attraction of the bar (disre- 



