THE PHILOSOPHICAL BASIS 29 



tional language justified above as a matter of 

 convenience, like causes always produce like 

 effects in like circumstances, science, and indeed 

 all organised knowledge, would be impossible. 



When fitted into our mental picture, a 

 generalised result of experience is known as a 

 physical law, or, to change the form of a word 

 and the size of two letters, as a Law of Nature. 

 Many brave things have been written, and many 

 capital letters expended in describing the Reign 

 of Law. The laws of Nature, however, when 

 the mode of their discovery is analysed, are seen 

 to be merely the most convenient way of stating 

 the results of experience in a form suitable for 

 future reference. The word 'Maw" used in this 

 connection has had an unfortunate effect. It 

 has imparted a kind of idea of moral obligation, 

 which bids the phenomena ''obey the law," and 

 leads to the notion that, when we have traced 

 a law, we have discovered the ultimate cause of 

 a series of phenomena. Newton and Ohm did 

 not first promulgate and then enforce the regula- 

 tions which are associated with their names, 

 though it is not only elementary students who 

 may be heard saying that a stone falls to the 

 ground "because of the law of gravitation." 

 We must still ask why each particle of one body 

 attracts each particle of another, even if there 

 be a force between them proportional to the 

 product of the masses divided by the square of 

 the distance. We do not necessarily know why 

 the electric current through a conductor varies as 

 the applied electro-motive force, when we have dis- 

 covered how these two quantities are connected. 

 The great change in the rate of progress of 



