prior to the Introduction of the Potentials. 63 



of the magnetic body, so as to be incapable of passing from one 

 element to the next 



Suppose that an amount m of the positive magnetic fluid is 

 located at a point (x y, z) ; the components of the magnetic 

 intensity, or force exerted on unit magnetic pole, at a point 

 (, f, ) will evidently be 



-m-f-X -m~(-\ -m-(-) 



where r denotes ((? - xf + (n - ?/) 2 + (Z - z) 2 j*. Hence if we 

 consider next a magnetic element in which equal quantities of 

 the two magnetic fluids are displaced from each other parallel 

 to_ the ic-axis, the components of the magnetic intensity at 

 (g, i|, 2) will be the negative derivates, with respect to ij, 

 respectively, of the function 



where the quantity A, which does not involve (f, j, ), may be 

 called the magnetic moment of the element : it may be measured 

 by the couple required to maintain the element in equilibrium 

 at a definite angular distance from the magnetic meridian. 



If the displacement of the two fluids from each other in the 

 element is not parallel to the axis of x t it is easily seen that the 

 expression corresponding to the last is 



where the vector (A, B, C) now denotes the magnetic moment 

 of the element. 



Thus the magnetic intensity at an -external point (, 77, ) 

 due to any magnetic body has the components 



; - 017 

 where 



ex oy 

 integrated throughout the substance of the magnetic body, and 



