989 



two of us probably having the same idea of that. The impact of a 

 violent sensation does convey to us the impression of physical motion. 

 We feel stunned by a very loud sound, and we say of a very bad 

 smell, it is enough to knock one down. We also feel dazed and stunned 

 by a sudden piece of bad news. If we were not allowed to experience 

 the sensation of sound before reaching adult age, I think the sensation 

 would appear to us very different from what it now docs, and would con- 

 tain a large impression of physical agitation. We do not know that 

 such impression is not all there is in the sensation as experienced by 

 the simplest organisms, Coelenterata for example. The tones of motion 

 which give us the sensation of sound are those of such rapidity that a 

 definite sensation of one stroke has not time to occur before the impact 

 of the next. The tones below those made by 16 strokes to the second, 

 appear to us simply so many detached blows of a ponderable body, 

 while such idea is entirely eliminated from those above that pitch, an 

 effect due solely to a mechanical cause. In the case of heat and light 

 the principle is the same, but exhibited to a much greater degree, their 

 pulsations being almost infinite compared with those of sound. Where 

 the pulsations are, so far as our sensory apparatus is concerned, practically 

 superposed upon each other, the effect may be compared to a pressure 

 ^ajiher than a blow, in which case the different sorts of sensation would 

 ^present different sorts and degrees of pressure. Now we could not 

 36sibly have any antecedent notion of what we ought to consider as a 

 '\ trace of resistance or motion " in a sensation. The manner in which 

 the sensation behaves may for aught we know be precisely that which 

 should indicate to us motion of the particular sort of matter involved. 

 Extension we do not look for in sensation since it is not a thing or sub- 

 stance any more than is the motion that gives rise to heat and light. 

 But where any sort of phenomenon has a beginning and an ending in 

 time, it is certainly not an entity, but the motion of something. The 

 very terms beginning and ending imply motion. 



We often fail to recognize the difference between the sensation and 

 the objective movement which produces it. We are very apt to think 

 of light for example as objective, and imagine that our sensation of 

 light is something else and different, whereas the fact is, that light is 

 the sensation itself. Various degrees of heat and various tones of light, 

 as red, orange, yellow, green, blue, indigo and violet, are in reality so 

 many sensations, and all of them the subjective sequels of the same 

 sort of vibrant energy, viz. , solar radiation, each sensation representing 

 a different rate of vibration. Why one of these sensations should bo 

 heat and another one gieen, we cannot possibly know. All we can say 

 is that the mode of motion comimmirtited to certain of our tissues we 

 call heat, and that communicated to curtain others, green. That it is a 



