June 20, 1878] 



NATURE 



211 



name of special natural scUme, are tied to certain circles of 

 objects of study, and the truths they have established are valid 

 only for these circles. Even that generalisation of the so-called 

 organic natural sciences, which is designated as biology, cannot 

 very well be called a general natural science, because if indeed 

 anywhere else than upon the earth there exists something 

 similar to what we call life here, there is yet but little pro- 

 bability that the laws of terrestrial life may be applied to that 

 life of other worlds. 



The common task of general natural science — of physics and 

 chemistry, therefore — is the investigation of matter, of its pro- 

 perties, its changes, and of the laws of these changes ; and the 

 laws recognised by them must be applicable wherever there is 

 matter at all. 



Now with regard to the difference between physics and cheniis- 

 try, it strikes the superficial observer that modern physics treat?, 

 in a more general manner, of the properties and changes of 

 properties of bodies, and in doing so that it contemplates the 

 separate bodies only as the bearers of the properties ; while 

 chemistry studies the separate bodies differing with regard to 

 their material, and that it touches their properties only inasmuch 

 as they appear necessary for distinguishing the bodies. One 

 might be inclined to found a definition of the two disciplines 

 upon these difference?. But when we enter more deeply into the 

 subject we shall see that the essential differences must be looked 

 for elsewhere. 



Of all conceptions which the human mind could form regarding 

 the essence of matter, only the hypothesis of discrete mass- 

 particles, the atomistic hypothesis therefore, has led to an intel- 

 ligible explanation of facts. Even if nobody who has followed 

 the scientific discussions of the latest time, can deny that the 

 tendency of natural scientific reflection just now again lies in the 

 direction of reducing the differences of materiSs to dynamic 

 causes, yet we must certainly own that at present the observed 

 facts can be deduced as necessary consequences from the atomistic 

 theory only. On this point physicists and chemists are no doubt 

 agreed. And if even modern representatives of speculative 

 philosophy concur in the view that all natural knowledge leads 

 to the mechanics of atoms in the last instance, then we may 

 doubtless use the atomistic theory preliminarily as the basis of 

 further reflections in the domain of natural science and, for the 

 present at hast, found upon it the definition of the separate 

 branches of natural science, be it on'y in order to render a clearer 

 account to ourselves of their tenour and of the limits of their 

 domains. Now the sum total of all knowledge obtained with 

 regard to matter has led to the following maxims of ths atomistic 

 theory. 



We must imagine that matter consis's of small particles, uniform 

 in their material and not further divisible, not even by chemical 

 processes, — of atoms. These atoms accumulate in consequence of 

 forces inherent in them or acting upon them, and thus produce 

 systems of atoms, or jnolecules. In the gaseous state these mole- 

 cules move about in space as isolated beings, in the o'.her aggre- 

 gate states an attraction of molecules also becomes apparent, 

 and thus the masses originate which are able to act upon our 

 senses directly. 



If this conception of the essence of matter is taken as a basis 

 then we may define chemistry as ths science of atoms, and physics 

 as the science of molecules, and it lies near then to look upon that 

 part of modern physics which treats of masses as a separate 

 discipline, and to reserve for it the name of mechanics. Thus 

 mechanics appears as the fundamental science of physics and 

 chemistry, inasmuch as both are obliged to treat their moleo«les 

 cr atoms respectively as masses in certain considerations, and 

 particularly in calculations. Mechanics, physics, and chemistry, 

 however, are the bases of all special natural sciences, because it 

 is evident that all changes, no matter whether they occar, in the 

 great cosmos, or in the microcosmos of the ve^^etable or animal 

 body, can but be of a mechanical, physical, or chemical nature. 

 Now from the fact that chemistry has to do with the study of 

 atoms, of the building stone-, the.efore, of which ths molecules 

 are constructed which physics treats as a whole, it results directly 

 that the theoretical investigations of chemistry offer more diffi- 

 culties than those of physics, and that theoretical chemistry can 

 progress in certain directions only after theoretical-physical 

 knowledge has sufficiently advanced. The comparatively low 

 state of theoretical chemistry thus seems not only pardonable 

 but natural, and it becomes clear why for the present theoretical- 

 chemical investigation has principally turned its attention to those 

 . questions which are more or less independent of physics. Thus 

 we understand why chemical dynamics is as yet an alm:st uncul- 



tivated field upon which the mittrlals, which are heaped up in 

 immense profusion could, up to the present, not find a theoretical 

 treatment, while on the domain of chemical statics ripe, or at 

 least partly-developed fruits, were reaped in plentiful quantity. 



It will not be difticult to show that chemistry and chemists 

 have, in this direction, materially contributed towards the progress 

 of the general doctrine of atoms, therefore towards the progress 

 of our knowledge of the nature of matter. 



Since the (as far as we know) first foundations of the scientific 

 observation of nature were laid by Democritus, the most ele- 

 mentary maxims of the theory of matter have remained the same. 

 " From nothing nothing can come ; nothing that is can be anni- 

 hilated; all change is only combination or separation of par- 

 ticles." But the atomistic theory of antiquity was more a 

 precursor of the views which we now designate in physics as the 

 molecular theory ; it contained, even in its further development, 

 no fundamental thought of a specially chemical theory. 



The first fundamental maxim of scientific chemistry was pro- 

 nounced towards the end of the seventeenth century by the 

 chemist Boyle, who was first to define the conception of the 

 chemical element as that which is not further divisible into ma- 

 terially different parts. It will not matter whether many or 

 perhaps all the bodies which we now consider to be chemical 

 elments may be found to be further divisible in the progress of 

 knowledge — although there is at present no real indication for 

 this — the idea of the chemical element will always remain 

 unaltered. 



With this idea of the chemical element that old conception 

 of the indestructibility of matter was then connected, and thus 

 the further fundamental maxim of chemistry originated, of the 

 invariability of elements, which has not further been questioned 

 since Lavoisier's celebrated experiments on the often- pretended 

 change of water into earth, and which finds its confirmation in 

 all chemical facts. 



From these views the chemical atom'c theory arose at the 

 beginning of the nineteenth century, and the English chemist 

 Dalton is with right regarded as its founder. While, after 

 Democritus, the difference of all things is caused by the dif- 

 ference of their atoms in number, size, shape, and order, a 

 qualitative difference of atoms, however, does not exist, Dalton 

 first in a definite manner supposed the existence of qualitatively 

 different elementary atoms. He was first to ascribe to these 

 qualitatively different atoms certain weights which are character' 

 istic for the various elements ; he first showed that these relative 

 atomic weis^hts may be determined by chemical study. 



As the conception of the chemical element so will also the 

 conception of the chemical atom, as that quantity of elementary 

 matter tvhlch is not furth:r divisible by chemical processes, remain 

 for ever. For chemistry, the question whether the chemical 

 atoms are originally units {einheitliche) and absolutely indivisible 

 beings, is of no importance. Let the proof be given that the 

 chemical atoms are formed of particles of a finer or Jer, or let 

 the theory of revolving rings founded by Thomson, or some 

 other similar conception which understands atoms to result 

 from continuous matter, be proved in the progress of know- 

 ledge, the conception of chemical atoms will not be altered or 

 annihilated. The chemist will always welcome an explanation 

 of his units, because chemistry requires atoms only as a starting 

 point, not as an end. 



Dalton's atomic theory from the very first suffered from a 

 certain imperfection which consisted in its speaking of the atoms 

 of compound bodies as well as of those of elementary ones and 

 thus did not distinguish the ideas of atom and molecule. For 

 the first period, during which the foundations of chemical science 

 had to be completed, no essential harm arose from this want of 

 clearness, but later on, when the structure was to be developed 

 farther, it caused considerable confusion. 



It is true that already in iSii Amadeo Avogadro pronounced 

 the maxim that gaseous bodies contain an equal number of 

 molecules in equal spaces, and that even the molecules of 

 elementary substances consist of several atoms, and that in 181 4 

 the French physicist Ampere arrived at the same conclusions ; 

 but this idea, which was so fertile in the future, hardly attracted 

 any notice at first. In its application it led to contradictions 

 which seemed insolvable at that time, and it was therefore aban- 

 doned, although the great chemist Damas hai taken it for some 

 time as the base of his considerations. More than that, it was 

 forgotten until forty years later the Italian chemist Cannizzaro 

 recalled to the memory of his colleagues the merits of his 

 countryman. 

 In the meantime chemists first, and later on physicists as ^^ell, 



