ERRORS OF 'COMMON SENSE.' 119 



imagined by science, and now held to account for the 

 radiometer ? In the glass bulb which has been exhausted 

 to such a degree that ' common sense ' would pronounce it 

 to be quite empty we must conceive there are innu- 

 merable smooth elastic spheres, the molecules of the resi- 

 dual gas, dashing about in apparent confusion, with sixty 

 times the velocity of an express train, and hitting each 

 other millions of times in a second. Will the 4 common 

 sense of mankind ' consider this a rational doctrine ? Again, 

 both inside this empty space and outside it, between the 

 reader and the paper before him, between the earth and 

 the sun occupying all the interplanetary space farther than 

 the eye can reach, or indeed the mind can conceive, there 

 is assumed to be a something indefinitely more elastic and 

 immeasurably more solid than tempered steel, a medium 

 in which suns and worlds move without resistance. Is 

 not such a doctrine utterly incredible to the ' common 

 sense of mankind ? ' Yet the kinetic theory of gases and 

 the undulatory theory of light are accepted as true by 

 nine-tenths of the scientific men of the present day ; and, 

 doubtless, in the processes of scientific evolution in the 

 coming times many a discovery will be brought to light 

 to give a sharp shock to ' the common sense of educated 

 mankind.' l Common sense is frequently superficial, and 

 only apparent sense, and sometimes quite opposed to 

 actual fact ; and there is no necessary connection between 

 it and truth. 



One of the most fruitful sources of error and strife, 

 which (although it does not often occur in the simple 

 sciences) it is necessary for a scientific investigator to 

 avoid, is the assertion of unproved hypotheses as if they 

 were proved truths ; and if such hypotheses flatter the 



1 Crookes, Another Lesson from the Radiometer,' Nineteenth Cen- 

 tury Review, p. 889, July 1877. 



