Feb., 1889. 
spencer’s 
FIRST PRINCIPLES. 
37 
; 4 
J 5 
condition of affairs that lie may continue the work of 
explanation, i.e., of detection of hidden similarities. For 
instance, a solid body is, to our senses, a continuous something 
entirely filling up a space. If it is heated it expands ; if it is 
soluble in water, it disappears when put in water. If we 
make no hypotheses, we can go no further. The expansion of 
a continuous solid is unlike anything else, and is therefore 
inexplicable ; but I hold—and here I think Mr. Spencer 
would consider me quite hopeless—that there is no difficulty 
whatever in conceiving of the expansion of continuous matter. 
Again, the disappearance of the continuous salt in continuous 
water is inexplicable, but I have no sense warrant that it is 
not going on, and I may be driven to attempt to conceive it. 
But now let me introduce the unverifiable, or, at least, 
unverified, hypothesis that matter is discontinuous, and really 
consists of separated particles, and I can explain expansion :— 
it resembles the scattering of a crowd. I can explain 
solution :—it resembles the mixing of two crowds, and so on. 
Again, we have recognised various forms of energy— 
kinetic, affecting the sight in one way, or light affecting it in 
another way, or heat affecting the temperature sense, but we 
cannot say that any one of these resembles any other. 
Without hypothesis they are inexplicable. But, let me 
suppose that the ultimate particles of matter possess both 
strain and kinetic energy, and that, when they bump against 
my skin, they affect my temperature sense, and I explain heat. 
I show that a hot body resembles known mechanical systems. 
Or, let me suppose that even where I cannot see or feel matter 
there is still something which can be acted on by the ultimate 
particles of matter and receive energy from them, and I can 
explain light as being waves sent out in this intangible some¬ 
thing by the vibrating atoms. I show that it resembles other 
cases of waves sent out from vibrating sources in water or 
in air. 
No doubt this longing for explanation which possesses us 
is in part strengthened by our belief in identity. If energy 
is continuous in its existence, then we suppose that in itself 
it must be the same in kind, though now it affects one sense, 
now another, and now none at all. We go on from this 
another step and suppose that if we could only train our 
senses sufficiently we should be able to follow the energy 
through all its transmigrations, and see it ever the same in 
kind. The senses used in the investigation of visible motion, 
the muscular sense, the touch, the eye, are the most 
thoroughly trained, and work best together. We, therefore, 
naturally fix on these as the senses which are, in imagination, 
to follow the energy up, and so our hypotheses are constructed 
