348 



NATURE 



\_Aug. 27, 1874 



a century ago, and which governs the form of the combinations. 

 The atoms of the various simple bodies are not endowed with the 

 same aptitude for combination with each other ; they are not 

 equivalent to each other. This is what is called atomicity, and 

 the fundamental property of atoms is without doubt connected 

 with the various modes of motion by which tliey are animated. 

 When these atoms combine with each other, their movements 

 require to be reciprocally co-ordinated, and this co-ordination 

 determines the form of the new systems of equilibrium which will 

 be formed ; that is, the new combinations. 



It is with atoms thus endowed that chemists now construct 

 molecular edifices. Resting at once upon the data of analysis 

 and on the investigition of reactions, they express the composition 

 of bodies by formulx' which mark the nature, the number, and 

 the arrangement of the atoms which each molecule of these 

 bodies contains. But what ! is this merely an ingenious exercise 

 of the mind? and the construction of formul;c by means of these 

 symbolic materials which are selected, which are arranged so as 

 to give to the molecular edifice a determined form, — is this a 

 mere matter of curiosity ? IJy no means. These formula.', by 

 whose aid are expressed the composition of bodies and the con- 

 stitution of their molecules, offer also a valuable aid for the 

 interpretation of their projierties, for the study of their metamor- 

 phoses, for the discovery of their reciprocal relations, — all things 

 which are intimately connected in each body with the nature 

 and arrangement of the atoms. Now, the investigation and com- 

 parison of these formuhu furnish to the inquiring spirit the ele- 

 ments of a powerful synthesis. What treasures have been 

 acquired by science by this process, which consists in deducing 

 the transformations of bodies from their molecular structure, and 

 in creating, by a sort of intuition, new molecules by means of 

 those already known ! The artificial formation of a number of 

 combinations, the syntheses of as many organic compounds as 

 nature alone seemed to have the privilege of forming — in a word, 

 the greater part of chemical discoveries which liave enriched 

 science and the world for twenty years — are founded on this 

 inductive method, the only efficacious and the only rational one 

 in the sciences. I shall cite only one e.xample among many 

 others. 



A happy chance led to the discovery of that brilliant substance, 

 of a bright purple, which is known under the name of fuchsine 

 or rosaniline. Analysis determines its composition, skilled inves- 

 tigations find its molecular structure. Soon it is known how to 

 modify it, to multiply the number of its derivatives, to vary the 

 sources of their production, and from attentive study of all these 

 reactions, issue a pleiad of analogous substances whose diverse 

 colours rival in brilliancy the richest lints of the rainbow. A 

 new and powerful industry has already resulted from all these 

 investigations, which theory has followed step by step and guided 

 the fertile evolution. In this order of investigation, science lias 

 recently gained one of her most striking triumphs. -She has 

 succeeded in forming at once the colouring matter of madder 

 (alizarin). By an ingenious combination of reactions, and by 

 theoretic reasonings still more ingenious, MM. Graebe and 

 Liebermann have succeeded in obtaining this body synthetically, 

 by means of anthracene, one of the numerous bodies which is 

 now obtained from coal-tar, the impure source of so many won- 

 ders. Such is a discovery which has issued from the womb of 

 science, and of science the most abstract ; confirming precon- 

 ceived ideas on the relations of composition and of atomic struc- 

 ture between anthracene, alizarin, and the intermediate terms. 

 And this ^vill not be the last product of this beautiful develop- 

 ment of chemistry. Future conceptions on the intimate structure 

 of complex organic compounds will be so many landmarks for 

 new syntheses, and hypotheses rigorously deduced from acquired 

 principles will be fruitful in the happiest applications. 



Saccharine matters, alkaloids, other complex bodies whose 

 properties and diverse transformations are actively investigated 

 with a view of deducing their molecular constitution — all these 

 substances may be artificially reproduced, as s on as this pre- 

 paratory work, so difficult and often seemingly so useless, will 

 have sufficiently advanced. So fine a programme justifies the 

 great efforts which have been made, in our days, in this direc- 

 tion. To discover, to analyse, to study, to classify, to reproduce 

 artificially so many diverse substances, to study their internal 

 structure, to indicate their useful applications ; to surprise, in a 

 word, the secrets of Nature and to imitate her, if not in her pro- 

 cesses, at least in some of her productions — such is the noble aim 

 of contemporary science. She can only reach it by the sure but 

 slow paths we have indicated ; experiment guided by theory. In 

 chemistry, at least, empiricism has had its day ; problems, clearly 



stated, must be boldly faced, and henceforth the rational con- 

 quests of experiment will only leave a place more and more 

 circumscribed for fortunate finds and the surprises of the crucible. 

 Away, then, with the detractors of theory, who go in quest of dis- 

 coveries which they can neither foresee nor prepare ; they reap 

 where they have not sown. But you, courageous workers, who 

 trace methodically your furrows, I congratulate you. Vou may 

 be sometimes deceived, but your work will be fruitful, and 

 the goods wliich you amass will be the true treasure of science . 



Will not this science be one day embarrassed and as if encum- 

 bered with so much riches, and will the strongest memory be 

 able to support all the weight ? If the danger exists, there is no 

 need to fear it. The classification of all these materials will free 

 us from embarrassment. In a well-arranged edifice, each stone 

 requires to be prepared before taking its place ; but the con- 

 sruction accomplished, all do not strike the eye equally, though 

 each has its use ; only the strong courses, the corner-stones and 

 the salient parts, are noticed. It will be thus with tlie monument 

 of science. The details which have for their end to fill up gaps 

 will disappear in the great whole, of which we only need consider 

 the foundation, the principal lines, and the crowning of the 

 edifice. 



Gentlemen, chemistry thus constituted, and physics, have 

 between them necessary connections. Both the one and the 

 other investigate the properties of bodies, and it is evident that, so 

 far as the ponderable bodies are concerned, these properties must 

 be intimately connected with the constitution of matter. Hence 

 the atomic hypothesis which suffices for the interpretation of 

 chemical phenomena ought also to be adapted to physical 

 theories. This is the case. It is in the movements of atoms 

 and of molecules that we now seek, not only the source of the 

 chemical forces, but the cause of the physical modifications of 

 matter, changes of condition which it can undergo, phenomena 

 of light, of heat, of electricity, of which it is the support. 



Two French savans, Dulong and Petit, discovered some time 

 ago a very simple law which connects the weights of atoms with 

 their specific heats. It is known that the quantities of heat 

 necessary to change by one degree the temperature of the unit 

 of weight of bodies are very unequal. This is what we call 

 specific heats ; but the quantities of heat which bring about in 

 simple bodies, taken under conditions in which they are rigorously 

 comparable, the same variations of temperatures, are equal, if 

 we apply these quantities of heat not to the unit of weight but to 

 the atomic weight ; in other words, the atoms of these elementary 

 bodies possess the same 'specific heats, though their relative 

 weights are very unequal. 



But as to this heat which is thus communicated to them, and 

 which raises their temperature equally, what is in reality its mode 

 of action ? It augments the intensity of their vibratory move- 

 ments. Physicists recognise lieat as a mode of motion, and that 

 it comes under the cognisance of our perceptions by the vibra- 

 tions of atomic matter or ether ; of ether, that fluid material 

 perfectly elastic, incoercible, imponderable, which fills all the 

 immensity of space and the depth of all b(5dies. It is in 

 this fluid that the stars describe their orbits ; in this fluid 

 atoms perforin their movements and describe their trajec- 

 tories. Thus the ether, the radiant messenger of heat and 

 light, conveys and distributes their radiations through all 

 the universe ; and that which it loses in vibratory energy 

 when it penetrates a cold body, which it warms, it communi- 

 cates to the atoms of this body and augments the intensity of 

 their movements ; and that which it gains in energy by contact 

 with a warm body, which it cools, it withdraws from tills body 

 and diminishes the intensity of their. vibratory movements. And 

 this kind of light and heat which come from material liodies is 

 transmitted across space to other material bodies. You will 

 remember in reference to this the words which Goethe put into 

 the mouth of the Prince of Darkness in cursing the light — " It is 

 born of bodies, it is brought forth and maintained by bodies, 

 and it will perish with them." 



But this exchange of forces which circulate from ether to atoms 

 and from atoms to ether, must it manifest itself always in the 

 phenomena of light or heat? This vibratory force which is 

 transmitted by elfier, can it not be preserved and stored up by 

 matter, or appear under other forms ? 



It can be preserved as aftinity, liberated as electricity, trans- 

 formed into dynamic movements. It is this which is stored 

 up in the innumerable compounds elaborated by the vegetable 

 kingdom ; it is this which provokes the decomposition of 

 carbonic acid and of the vapour of water by the most delicate 

 organs of plants which blossom in the sunlight. Originating 



