318 



FALLACIES. 



require any proof, that "a thing cannot act where it is not." 

 With this weapon the Cartesians waged a formidable war 

 against the theory of gravitation, which, according to them, 

 involving so obvious an absurdity, must be rejected in limine: 

 the sun could not possibly act upon the earth, not being there. 

 It was not surprising that the adherents of the old systems 

 of astronomy should urge this objection against the new ; 

 but the false assumption imposed equally on Newton himself, 

 who in order to turn the edge of the objection, imagined a 

 subtle ether which filled up the space between the sun and the 

 earth, and by its intermediate agency was the proximate cause 

 of the phenomena of gravitation. " It is inconceivable," said 

 Newton, in one of his letters to Dr. Bentley,* " that inanimate 

 brute matter should, without the mediation of something else, 

 which is not material, operate upon and affect other matter 

 without mutual contact. . . . . That gravity should be 

 innate, inherent, and essential to matter, so that one body may 

 act on another, at a distance, through a vacuum, without the 

 mediation of anything else, by and through which their action 

 and force may be conveyed from one to another, is to me so 

 great an absurdity, that I believe no man, who in philosophical 

 matters has a competent faculty of thinking, can ever fall into 

 it." This passage should be hung up in the cabinet of every 

 cultivator of science who is ever tempted to pronounce a fact 

 impossible because it appears to him inconceivable. In our 

 own day one would be more tempted, though with equal in- 

 justice, to reverse the concluding observation, and consider 

 the seeing any absurdity at all in a thing so simple and 

 natural, to be what really marks the absence of " a competent 

 faculty of thinking." No one now feels any difficulty in con- 

 ceiving gravity to be, as much as any other property is, 

 " inherent, and essential to matter," nor finds the comprehen- 

 sion of it facilitated in the smallest degree by the supposition 

 of an ether (though some recent inquirers do give this as an 

 explanation of it) ; nor thinks it at all incredible that the celes- 

 tial bodies can and do act where they, in actual bodily presence, 



* I quote this passage from Playfair's celebrated Dissertations on the Pro- 

 gress of Mathematical and Physical Science. 



