ioo THE LIMITATIONS OF SCIENCE 



made by Descartes. We may admit with Lord Kelvin 

 that we know nothing about the real nature of elec- 

 tricity. We do know experimentally that electricity 

 seems to be associated always with matter ; the greatest 

 velocity we have caused or observed any body of an 

 appreciable size to have, is one thousand eight hun- 

 dred times less than the speed of light. An ethereal 

 plenum is certainly only a matter of imagination, and 

 the conception of matter as a strain in this imaginary 

 plenum is hardly a clear idea. So it seems that the 

 facts supporting our modern postulates regarding the 

 nature of substance are as meager and doubtful, and 

 our ideas as obscure for our purpose, as those of Des- 

 cartes were for his. 



On the contrary, it is no exaggeration to say that 

 there probably never lived a man better equipped than 

 Descartes to make and to defend an hypothesis; his 

 scientific skepticism, his freedom from the trammels 

 of authority, his devotion and skill in experimental 

 work, his determination to submit his id 'as to the 

 rigorous logic of mathematical analysis in which he 

 was the leader of his age, were admirable qualities for 

 such a purpose. A man who doubts even his own 

 existence, is not likely to adopt other ideas lightly. To 

 strip matter of every quality except mere extension; to 

 abolish every cause of phenomena except linear mo- 

 tion and the impact of bodies, both of which are 

 capable of the most accurate experimental investiga- 



