Galvanometer Deflection. 



409 



allowing it to cool apart from magnetic influence, or by some 

 other equivalent process of molecular revolution. 



A closer' examination into the behaviour of an elongated 

 magnet further confirms the above theory. Let us take as 

 type of such a magnet a very elongated ellipsoid of revolution 

 magnetized parallel to its axis, and suspended from a point in 

 its equator. Let o £ be the plane of the galvanometer-wind- 



Fig. 4. 



ings, o F the direction of the resultant magnetic force (F) 

 when there is no current, o X the direction of the axis of the 

 magnet at any time, 



« = Fof, 



e = Xof, 



m= permanent magnetic moment, 

 tc = coefficient of induced magnetization, 

 Y = volume of magnet, 

 i = current at any time t, 

 g = constant of galvanometer, 

 n = number of breaks per second in primary. 



The component forces parallel to oX and oYat time t tending 

 to magnetize the needle inductively are 



X=gi sin 6 + F cos (6 — a), 



Y=gicosd — Fsin(# — a). 



Hence (see Maxwell's ( Electricity,' vol. ii. pp. 65 & 67) the 

 couple tending to increase 6 is 



\ 1 + W ! + »»" _Fsin2(0-«)}. 



Y 



