SCIENCE. 
185 
IV. Caloric consists in certain vibrator)- motions in the 
molecules of ponderable matter or substances grosser than 
the ether, and these motions are not undulatory. 
V. The motions in ponderable matter which constitute 
Caloric set up or propagate in pure ether the undulatory 
vibrations which constitute light. 
VI. Conversely the undulatory vibrations in pure ether 
which constitutes Light set up or propagate in grosser matter 
the motions which are Caloric. 
VII. But the motions in pure ether which are Light cannot 
set up or propagate in all ponderable matter equally the 
motions which are Caloric. Transparent substances allow 
the ethereal undulations to pass through them with very little 
Caloric motion being set up thereby ; and if there were any 
substance perfectly transparent, no Caloric motion would be 
produced at all. 
VIII. Caloric motions in ponderable matter can be and are 
set up or propagated by other agencies than the undulations 
of ether, as by friction, percussion, &c. 
IX. Caloric, therefore, differs from Light in being (1) mo- 
tion in a different medium or in a different kind of matter ; 
(2) in being a different kind of motion ; (3) in being produc- 
ible without, so far as known, the agency of Light at all. I 
say “ so far as known,” because as the luminiferous ether 
is ubiquitous, or as, at least, its absence cannot anywhere be 
assumed, it is possible that in the calorific effects of percus- 
sion, friction, &c., undulations of the ether may be always 
an essential condition of the production of Caloric. 
It follows from these propositions that there are essential 
distinctions between Light and Heat, and that the effect of 
luminiferous undulations or “ Radiant ” Heat in producing 
Caloric in ponderable matter depends entirely upon, and 
varies greatly in accordance with, the constitution or struc- 
ture of the substances through which it passes, or .upon 
which it plays. 
The same fundamental distinction applies to those ethereal 
undulations which produce the effects called Chemical. 
No such effects can be produced upon substances except ac- 
cording to their special structure and properties. Their 
effect, for example, upon living matter is absolutely different 
from the effect they produce upon matter which does not 
possess vitality. The forces which give rise to chemical af- 
finity are wholly unknown. And so are those which give 
rise to the peculiar phenomena of living matter. The rays 
which are called Chemical may have no other part in the re- 
sult than that of setting free the molecules to be acted upon 
by the distinct and separate forces which are the real sources 
of chemical affinity. 
What, then, have we gained when we have grouped to- 
gether, under one common definition, such a variety of 
movements and such a variety of corresponding effects? 
This is not the kind of unity which we see and feel in the 
vast system of adjustments between the sun, the medium 
conveying its vibrations, and the effect of these on all the 
phenomena of earth. The kind of unity which is impressed 
upon us is neither that of a mere unity of material, nor of 
identity in the forms of motion. On the contrary, this kind 
of unity among things so diverse in all other aspects is a 
bare intellectual apprehension, only reached as the result of 
difficult research, and standing in no natural connection 
with our ordinary apprehension of physical truth. For our 
conception of the energies with which we have to deal in 
Nature must be molded on our knowledge of what they do, 
far more than on any abstract definition of what they are ; 
or rather, perhaps, it would be more correct to say that 
our conception of what things are can only be complete 
in proportion as we take into our view the effects which 
they produce upon other things around them, and espe- 
cially upon ourselves, through the organs by which we 
are in contact with the external world. , If in these effects 
any two agencies are not the same — if they are not even 
alike — if, perhaps, they are the very antithesis of each other 
— then the classification which identifies them, however cor- 
rect it may be, as far as it goes, must omit some character- 
istics which are much more essential than those which it 
includes. The most hideous discords which can assail the 
ear, and the divinest strains of heavenly music, can be re- 
garded as identical in being both a series of sonorous 
waves. But the thought, the preparation, the concerted 
design — in short, the unity of mind and of sentiment, on 
which the production of musical harmony depends, and 
which it again conveys with matchless power of ex- 
pression to other minds — all this higher unity is con- 
cealed and lost if we do not rise above the mere 
mechanical definition under which discords and harmon- 
ies can nevertheless be in this way correctly classed to- 
gether. And yet so pleased are we with discoveries 
of this kind, which reduce, under a common method 
of conception, things which we have been accustomed to 
regard as widely different, that we are apt to be filled with 
conceit about such definitions, as if we had reached in them 
some great ultimate truth on the nature of things, and as if 
the old aspects in which we had been accustomed to re- 
gard them were by comparison almost deceptive ; whereas, 
in reality, the higher truth may well have been that which 
we have always known, and the lower truth that which we 
have recently discovered. The knowledge that Light and 
Heat are separable, that they do not always accompany 
each other, is a truer and juster conception of the relation 
in which they stand to us, and to all that we see around us, 
than the knowledge that they are both the same in respect 
of their being both “ modes of motion.” To know the work 
which a machine does is a fuller and higher knowledge 
than to know the nature of the materials of which its parts 
are composed, or even to perceive and follow the kind of 
movement by which its effects are produced. And if there 
be two machines which, in respect to structure and move- 
ment and material, are the same, or closely similar, but 
which, nevertheless, produce totally different kinds of 
work, we may be sure that this difference is the most real 
and the most important truth respecting them. The new 
aspects in which we see their likeness are less lull and less 
adequate than the old familiar aspects in which we regard 
them as dissimilar. 
But the mind is apt to be enamored of a new conception 
of this kind, and to mistake its place and its relative im- 
portance in the sphere of knowledge. It is in this way, 
and in this way only, that we can account for the tendency 
among some scientific men to exaggerate beyond all 
bounds the significance of the abstract definitions which 
they reach by neglecting differences of work, of function, and 
of result, and by fixing their attention mainly on some 
newly discovered likeness in respect to form, or motion, 
or chemical composition. It is thus that because a partic- 
ular substance called “Protoplasm” is found to be pres- 
ent in all living organisms, an endeavor follows to get rid 
of Life as a separate conception, and to reduce it to the 
physical property of this material. The fallacy involved 
in this endeavor needs no other exposure than the 
fact that, as the appearance and the composition of this 
material is the same whether it be dead or living, the Pro- 
toplasm of which such transcendental properties are af- 
firmed has always to be described as “ living” protoplasm. 
But no light can be thrown upon the facts by telling us 
that life is a property of that which lives. The expression 
for this substance which has been invented by Professor 
Huxley is a better one — the “ Physical Basis of Life.” It 
is better because it does not suggest the idea that Life is a 
mere physical property of the substance. But it is, after 
all, a metaphor which does not give an adequate idea of the 
conceptions which 'the phenomena suggest. The word 
“basis” has a distinct reference to a mechanical support, 
or to the principal substance in a chemical combination. 
At the best, too, there is but a distant and metaphorical 
analogy between these conceptions and the conceptions 
which are suggested by the connection between Protoplasm 
and Life. We cannot suppose Life to be a substance sup- 
ported by another. Neither can we suppose it to be like a 
chemical element in combination with another. It seems 
rather like a force or energy which first works up the inor- 
ganic materials into the form of protoplasm, and then con- 
tinues to exert itself through that combination when 
achieved. We call this kind of energy by a special name, 
for the best of all reasons, that it has special effects, differ- 
ent from all others. It often happens that the philosophy 
expressed in some common form of speech is deep and 
true, whilst the objections which are made to it in the name 
of science are shallow and fallacious. This is the case 
with all those phrases and expressions which imply that 
Life and its phenomena are so distinguishable from other 
things that they must be spoken of by themselves. The 
