186 Mr. G. Hookham on Permanent Magnet Circuits. 



Sir William Thomson, in a paper on units of measurement, 

 contemplates a time when many of the units we now employ 

 will become things of the past by the introduction of the 

 universal gravitation method of connecting mass with length 

 and force. 



The naming of particular units employed for a time in the 

 process of this development cannot but retard its progress, 

 and the unity of science should take place independently of 

 the subdivisions which may exist to-day. 



It is highly probable that chemical science may soon require 

 a modification of our present units, and we must not keep 

 combining weights, atomic heat, and so on, uncorrelated 

 with the rest of the body of science because the development 

 of science has taken the order it has done. It might have 

 been quite otherwise. 



Dr. Whewell entertained a speculation as to w^hether the 

 laws of motion would ever have been discovered by an intel- 

 lectual race of jelly-fish inhabiting a world in which were no 

 solid bodies. 



In like manner we may imagine that had Torpedoes, or 

 other animals armed with a controllable electrical equipment, 

 won the race for supremacy against man, the laws of electri- 

 city might have been reached before the mechanical laws. 

 Faraday and Maxwell would have preceded Galileo and 

 Newton, and Gymnotus might have exhibited in submarine 

 air-cases that uncanny biped Homo who could give you a 

 curious and mysterious shock with a stick or a stone. 



XX. On Permanent Magnet Circuits. 

 By George Hookham, M.A.* 



THE immediate object of my experiments in permanent 

 magnets was a practical one, viz. to obtain a magnetic 

 field suitable for the electromotor part of my electricity-meter. 

 If by their use a constant field of sufficient intensity could be 

 produced, its advantage in point of economy in use would 

 make it of the greatest -value. At "the same time I was aware 

 that the scientific world did not consciously believe in the 

 possibility of a really constant permanent magnet, except 

 when the magnetic circuit was complete through a magnetic 

 metal. 



But it occurred to me that there is one familiar case in 

 which absolute constancy is admitted, and yet this condition 

 is not fulfilled. I refer to the arrangement in which a soft 

 iron ring is cut at two points diametrically opposite, and the 



* Communicated by the Author, having been read before the Birming- 

 ham Philosophical Society, November 8, 1888. 



