SCIENCE. 



185 



IV. Caloric consists in certain vibratory 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 the}' 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 

 arc 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 scries 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 



