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magnetism are well explained by the contemporary theory, many seem 

 admirably clear; but none of these was or could have been witnessed 

 by the Greeks. We know much about the magnetic properties of 

 gases, dilute solutions, free atoms, elements and compounds which 

 are so feebly magnetizable that before 1830 they were not supposed 

 to be " magnetic ' ' at all ; we are still perplexed by the behaviour of iron 

 and lodestone. This is the reason why there are textbooks of magne- 

 tism, in which hundreds of pages are devoted to the data and the 

 theories of a number of effects most difficult to perceive and known to 

 none but physicists, while the magnets of daily experience are dismissed 

 with a chapter or two of mere description. As for electrified amber 

 and its kindred, they are fortunate to have a few paragraphs of any 

 modern treatise on electricity bestowed upon them. 



Frictional electricity is not a very striking phenomenon, nor is it 

 valuable in engineering; consequently it has been allowed to slip into 

 obscurity, shunned by cautious students on the hunt for problems 

 promising immediate returns. Ferromagnetism is not so unobtrusive. 

 Much of the electric machinery which has transformed the world since 

 Napoleon derives all its efficacy from certain blocks of iron or magnet- 

 izable alloy, enmeshed among the wires. So useful a property of 

 matter does not consent to lie neglected; physicists are forced to 

 hearken to its insistent demlands for attention. Ambition to achieve 

 some technical advance supplies a strong incentive; and there is a 

 feeling of humiliation that a quality of matter so conspicuous and 

 so remarkable, and so remarkably limited to a particular class of sub- 

 stances not in other ways exceptional, should not be properly connected 

 with the structure of contemporary physics. For these and other 

 motives, there are always physicists engaged in the struggle with the 

 problem of ferromagnetism — no mean struggle, for the difficulties are 

 truly serious. It was a tough problem which was offered to the Greeks 

 and which they rejected, when they saw the lodestone, took note of it, 

 and left it for the modern world to study. 



Some of the difficulties of ferromagnetism may be peculiar to it. 

 Others, it is to be feared, are examples of the troubles which are 

 reserved for scientists by the internal properties of solid bodies gener- 

 ally, and which physicists will some day be forced to confront when the 

 obvious problems of gases and free atoms are exhausted, if they are 

 not sooner incited by curiosity or by the requirements of engineering. 

 Most of the great conquests of recent physics have been achieved 

 through the study of gases, or of those properties of matter which are 

 the same for the solid as for the gaseous state. It is but natural to 



