MAGNETIC MASSES. 283 



that other views as to the nature of elementary actions lead to the 

 same conclusions, as regards the effects which we can measure 

 (if, for example, we abandon the idea of action at a distance), 

 we may consider these new views to be just as legitimate as 

 previous ones. 



293. MAGNETIC MASSES. The action of two poles at a given 

 distance depends on the special power of each of the magnets. 

 Experiment shows that the actions exerted on the poles of two 

 magnets by a given system are in a constant ratio ; we may consider 

 this ratio as being that of the magnetic masses of the two poles. It 

 follows from this definition, that the action of any given system on a 

 pole, is proportional to its magnetic mass; hence the reciprocal 

 action of two poles is separately proportional to the mass of each 

 of them that is, to the product of their magnetic masses. 



Calling these two masses m and m\ the action f, of the two poles 

 at the distance d, is 



mm' 



4> being a coefficient which depends on the choice of unit mass. In 

 order that this coefficient may be unity, we must take as unit mass 

 that of a pole, which, acting on an identical pole at unit distance, 

 exerts a repulsion equal to unit force. We have then 



mm ' 

 f = ~j?~ 



and the action is repulsive or attractive according as the poles are 

 of the same or of opposite kinds. 



If two poles of masses m and m', are connected with each other, 

 the action of the system thus formed on a third pole M placed at 

 distance d, which is very great in comparison with that of the two 

 poles, is equal to 



m'M 



it is proportional to the sum m + m of the two masses if the poles 

 are of the same kind, and to the difference m-m' if they are 

 different Magnetic masses can be added like algebraical quantities, 

 and we may affix to them the signs + and - as we can to electrical 



