2IO GREAT MEN OF SCIENCE 



bodies, and not in the interior of liquids, let alone gases. So 

 how could they be possible in the ether? This difficulty was 

 of course in reality only an imaginary one; it arose from an 

 unclear desire to ascribe the properties of matter to the 

 ether, although as Huygens had already expressly stated, it 

 could not be matter. 



In this case, and still even to-day, it is a fundamentally 

 crude materialism which stands in the way of an understand- 

 ing of nature; the belief then and now that everything must 

 possess the properties which have become familiar to us from 

 a study of matter, which study was at that time fairly far 

 advanced. If the investigation of nature - and at the same 

 time our whole mental development - is not to become in- 

 fertile, it is time that the opposite view should again be re- 

 garded as self-evident; that the laws of matter, or mechanics, 

 must remain entirely limited to matter, and that the ether and 

 everything belonging to it form a part of the world of a dif- 

 ferent nature, the peculiarities of which must be first dis- 

 covered piece by piece, in which process we shall meet with 

 surprises without end, as far as investigation is able to come 

 to grips with it. The desire to refer everything in the world 

 to mechanism, and the feeling of satisfaction whenever this 

 appears possible, was firmly ingrained in the Paris Academy 

 from the time of the Encyclopaedists. It received a fresh 

 and striking expression in Fresnel's time through Laplace's 

 Mecanique celeste. This work appeared to lay down the 

 principle that everything could be referred to the laws of 

 motion of matter as settled by Newton, together with New- 

 ton's law of gravitation, the similar laws of Coulomb, and the 

 molecular forces (which were also to hold for light and heat, 

 themselves regarded as simple substances). 



Fresnel had somehow or other to find a place for himself in 

 this theoretical structure, for the Paris Academy was his 

 only refuge. But his teacher in his experimental studies of 

 light was Nature. In order to pacify the Academy (perhaps 



