ch. xi.] THE QUESTION STATED. 273 



for scientific purposes, we are no more required to conceive 

 the action of matter upon matter in the case of gravitation 

 than in any other case of physical causation. All that the 

 hypothesis really asserts is that matter, in the presence of 

 other matter, will alter its space-relations in a specified way ; 

 and there is no reference whatever to any metaphysical 

 occulta vis which passes from matter in one place to matter 

 in another place. 



There is, however, no good ground for objecting to the 

 use of the phrase " attraction," provided it be employed only 

 as a scientific artifice. There is a certain sense in which 

 science, as well as legal practice, has its " fictions " that are 

 eminently useful. The lines and circles with which geometry 

 deals have nothing answering to them in nature; and the 

 analyst employs a " scientific fiction " when he deals with 

 infinitesimals, since it is impossible to conceive a quantity 

 less than any assignable quantity. In like manner, there is 

 nothing objectionable in using language which assimilates 

 the case of a planet revolving about the sun to the case of a 

 stone whirled at the end of a string; for there is real 

 similarity between the phenomena. So if the science of 

 chemistry had been obliged to wait until all the metaphysical 

 difficulties which encompass the conception of a molecule or 

 an atom had been cleared away, it might well have waited 

 until the end of the world. Quite likely the "atom" in 

 chemistry is as much a " scientific fiction " as the " infini- 

 tesimal" in algebra: but we cannot therefore complain of 

 the chemist for assigning to it shape and dimensions, pro- 

 vided he makes a scientific and not a metaplr, sical use of 

 the artifice. In the region of science such a fiction is no 

 more illegitimate than that fiction in the region of common- 

 sense by which I judge this writing-table to be solid, while, 

 for aught I know to the contrary, the empty spaces between 



calculum observationibus congruentem exhibeant." — See Lewes, Aristotle, 

 p. 92 ; Problems of Life and Mind, vol. i. p. 317. 



VOL. L T 



