On the Dimensions of a Magnetic Pole. 357 



established a connexion of the closest order between the aro- 

 matic portion of the molecule of lignin (bastose) and the tri- 

 atomic phenols — a fact which considerably strengthens the 

 views advanced by physiologists as to the correlations of the 

 carbohydrates with the aromatic group, and the reasoning by 

 which we have sought to emphasize them. The researches in 

 question, on this point, will be published in due course. 



XL. On the Dimensions of a Magnetic Pole in the Electrostatic 

 System of Units. By Oliyek J. Lodge, D.Sc. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 ri^HE discussion which has been carried on in your pages* 

 -L respecting the dimensions of a magnetic pole serves to 

 illustrate the divergency of thought between those in this 

 country who have been brought up, electrically, under Faraday 

 and Maxwell, and the continental philosophers so eminently 

 represented by Prof. Clausius. From one point of view the 

 discussion may be said to have been roused by a simple mare's 

 nest constructed by dropping a factor out of one side of an 

 equation (as was pointed out at once by Prof. Fitzgerald and 

 by Mr. J. J. Thomson) ; but from another point of view it is 

 the natural and inevitable consequence of the different aspects 

 from which these matters can be regarded: — the English 

 standpoint, in which the medium is recognized as the active 

 agent, and is continually present both in the mind and in the 

 formulas: and the continental standpoint, from which the 

 medium is perceived as so much empty space, and is taken 

 account of as such in the formulas. Both these aspects of the 

 subject are worth consideration; and it may be conducive to 

 future clearness to discuss them at moderate length. 



Coulomb's measurements provisionally established the fact 

 that in air the mechanical force between two electrically 

 charged bodies was proportional to ee' jr 1 \ but the subsequent 

 researches of Faraday proved that this proportionality only 

 holds so long as the medium enveloping the bodies is un- 

 changed, and that the above quotient must be multiplied by 

 different factors in order to give the force exerted in different 

 media. Thus if the same two charged bodies were immersed 

 in bisulphide of carbon, they would repel one another with 

 much less vigour than they do in air. 



Introducing therefore as a factor the electric inductive 



* Phil. Mag. [5] vol. xiii. pp. 376, 381, 427, 429, 431, 530 ; and vol. adv. 

 pp. 124 & 225. 



