22 Britain's Heritage of Science 



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it, more especially as it was much more thorough-going 

 than is generally represented. 



Matter is only known to us through the forces which 

 it exerts, and we cannot, therefore, reason about matter 

 at all, but only about forces. This truth was so strongly 

 impressed on Faraday's mind, that he warned scientific 

 men against the use of the word " atom," because it fixed 

 their attention on what he considered to be unessential. He 

 could only conceive centres of force and lines of force 

 emanating from these centres. Though all visible effects 

 are perceived at the termination of the lines, his whole 

 attention was fixed on the space which was filled by them. 

 He objected to all materialistic conceptions and looked upon 

 an all-pervading medium which had been invented to explain 

 the phenomena of light as an unnecessary and objectionable 

 imagination. He insisted that the lines of force which 

 spread out from a centre cannot be conceived to be made of 

 different stuff from the centres themselves, and that, therefore, 

 the aether, if it exist at all, must itself be made up of lines of 

 force emanating from separate centres. We may, perhaps, 

 regard this view as a dim foreshadowing of the most recent and 

 not yet firmly established views which have emerged from 

 the so-called principle of relativity. The vibration of light 

 Faraday tentatively suggested to be due to a vibration of 

 the line of force emanating from a centre, and therefore 

 forming an essential part of it. Each particle of matter 

 in his mind sends out tentacles through space, and when 

 two bits of matter seem to act on each other at a distance 

 they only appear to do so because their tentacles are in- 

 visible to us. During the closing days of his fertile" life 



r he planned experiments no doubt in connexion with his 

 -4 speculations on the nature of light to test whether magnetic 



*- force requires time for its propagation. 



Our belief in the conservation of energy now forms the 

 foundation of our conception of nature, and we hold to it 

 more firmly than to anything else that science has taught 

 us. All the changes we witness in the material world are 

 merely transformations of one form of energy into another, 

 and these different forms can all be measured in the same 

 units. The principle of conservation asserts that energy 



