THE QUESTION STATED 



ence, as well as legal practice, has its " fictions " 

 that are eminently useful. The lines and circles 

 with which geometry deals have nothing answer- 

 ing to them in nature ; and the analyst employs 

 a " scientific fiction " when he deals with in- 

 finitesimals, 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 " scien- 

 tific fiction " as the " infinitesimal " 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 metaphy- 

 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 its particles may be as much greater 

 than the particles as the interstellar spaces are 

 greater than the stars. We need have no hesi- 

 vol.ii 129 



