296 THE POPULAR SCIENCE MONTHLY. 



er somewhat out of the main lines of communication. Hobbes was, 

 moreover, a traveller, had lived much on the Continent, and had pos- 

 sibly met Galileo at Pisa. It was under the influence of these two 

 men, or rather of the methods they represented — Descartes and mathe- 

 matics, Galileo and the laws of motion — that Hobbes proceeded to 

 work out his philosophy. In the language of a distinguished profess- 

 or, to whom we look for an exhaustive account of Hobbes's relations 

 to the science of his time, "he set about reducing all his thoughts into 

 the unity of a system, whose central idea was this of motion, and 

 whose guiding principles were those of mathematical deduction." ^ 

 " His great postulate," says the same writer, " is motion or mutation," ^ 

 and he makes copious use of it within the sphere to which Aquinas 

 banished the experimental psychologist, and a little beyond. His ex- 

 planation of sensation is wholly mechanical. The crass materialism 

 with which he set out may have had something to do with his trench- 

 ant rejection of the audible, visible, and intelligible species of the 

 Schoolmen, but the hypothesis which replaced them betrays its own 

 origin. " The apparition of light," he says, " is really nothing but 

 motion within." ^ This thesis is more elaborately developed in a pas- 

 sage which we quote at length, as it appears to contain an anticipation 

 of the undulatory theory of light and heat : 



"From all lucid, shining, and illuminate bodies, there is a motion produced 

 to the eye, and, through the eye, to the optic nerve, and so into the brain, by 

 which that apparition of light and color is effected. . . . First, it is evident that 

 the fire . . . worketh by motion equally every way. . . . And further, that that 

 motion, whereby the fire worketh, is dilation, and contraction of itself alter- 

 nately ... is manifest also by experience. From such motion in the fire must 

 needs arise a rejection or casting from itself of that part of the medium which 

 is contiguous to it, whereby that part also rejecteth the next, and so successively 

 one part beateth back another to the very eye," and so from the eye to the optic 

 nerve, and from that to the brain.* 



This postulate of motion, applied in this thorough-going manner, led 

 Hobbes to a great discovery in the psychology of sensation. He 

 clearly demonstrated that the secondary qualities of body are purely 

 subjective, and his language is almost strong enough to lead us to be- 

 lieve that he would have gone a long way with Berkeley. For he 

 claims to have proved that " as in vision, so also in conceptions that arise 

 from the other senses, the subject of their inherence is not the object 

 but the sentient." If the w^ord " concej^tions" be interpreted accord- 

 ing to a definition previously laid down in the same treatise, in which 

 the " images produced by things " are described as conceptions, imagi- 

 nations, ideas, knowledge, it should seem that he might have applied 

 the analysis to the primary qualities as well, had the two sets of prop- 

 erties been as sharply contrasted as now, instead of being first dis- 

 1 Westinimier Hevieiv, April, 1867. ^ j^yi^^ 3 "Human Nature," p. 6 



4 Ibid., pp. e, 7. 



