[ 124 ] 



XIV. On the Dimensions of a Unit of Magnetism in the Elec- 

 trostatic System of Measures. By R. ClAUSIUS*. 



THREE articles in the June number of the Philosophical 

 Magazine, respecting my determination of the dimen- 

 sions of the electrostatic unit of magnetism, induce me to give 

 some further explanations on the point of view from which I 

 started in that determination. 



One of the greatest advances of physical science was Am- 

 pere's establishment of the connexion between magnetism and 

 current electricity, and his pointing out that, in respect of its 

 action, a small magnet can be replaced by a small closed elec- 

 tric current, of which the quantity and intensity stand in the 

 following relation to the strength of the magnet: — the pro- 

 duct of the intensity and the surface round which the current 

 flows is equal to the moment of the magnet. In consequence 

 of this principle, magnetism need no longer be regarded as a 

 peculiar and separately existing agent, but to the word mag- 

 netism a notion can be attached the definition of which is to 

 be drawn from electrodynamics. 



But then it is evident that this definition must be such as 

 to correspond with Ampere's proposition universally, and in- 

 dependently of the system of measures employed, and not 

 such that a current and a magnet which are equivalent when 

 one system is employed become of different values on the em- 

 ployment of another. On this condition I have based my 

 determination of the static unit of magnetism. 



Xow, with respect to Maxwell's treatment of the matter, he 

 has in several passages of his work quoted Ampere's proposi- 

 tion as a correct one, without anywhere adding any limiting 

 remark to the effect that the proposition is to be regarded as 

 valid only in the electrodynamic system, and not in the elec- 

 trostatic. His units, however, he has determined in such wise 

 that Ampere's proposition is satisfied only in the electrody- 

 namic system, while in the electrostatic the quantities which 

 according to Ampere should be equal are represented by ex- 

 pressions which have different dimensions, and hence their 

 values are changed in quite different ways by an alteration of 

 the fundamental units. 



How Maxwell arrived at his formula for the electrostatic 

 unit of magnetism, which deviates from Ampere's proposition, 

 it is impossible to say with certainty, as no explanation about 

 it is given in his work. Nevertheless, as I have already said 

 in my previous paper, it can be inferred from the context that 



* Translated from the German MS. communicated bv the Author. 



