March 12, 1908] 



NA TURE 



45 1 



bnyond, to determine the intrinsic constitution of tile 

 central nuclei to which they are attached, which may 

 remain permanently beyond our ken. The expansion of 

 our ideas about the atoms, and their structural connection 

 with the cether, was traced from their origin in Descartes, 

 ihrough Huygens and Newton, down to the more definite 

 modern types of representation, as regards various essential 

 features, that are afforded by the vortex atom and the 

 electron. 



In the hands of the physicists, especially Newton and 

 ■S'oung, the atom had already become a complex structure, 

 capable of definite, inherent, periods of free vibration, but, 

 so far as physics was concerned, the same substance might 

 include various kinds of atoms. The fundamental advance 

 of Dalton, which assured an adequate domain to chemistry 

 as an exact science, was the proof that each compound 

 substance is definite as regards its molecule, and that all 

 atoms of the same elementary body are identical. Whether 

 this absolute identity points to the atom of each chemical 

 element being a dynamically balanced structure of 

 primordial atoms, one of a limited number of possible 

 definite types of structure — which would be a perfectly 

 reasonable way of accounting for this remarkable identity 

 — remains an open question. The periodic relations of the 

 elements, connected most closely with the name of 

 ^[endeMeff, certainly indicate that, whatever may be the 

 case as regards the kernel, the outer structure of the atom, 

 so to speak, w^hich is the link through the fether between 

 the nucleus and the outside world, is constituted on the 

 basis of a common ultimate element which may be the 

 electron. 



The remark of Maxwell seems still to retain its force, 

 that the mechanism of biological evolution could hardly 

 reside in atoms, primordial or other, which had not much 

 vaster underlying complication than is needed for their 

 purely physical relations. The facts of biology may 

 possibly demand a hypothesis such as the above, that atoms 

 not in intimate contact interact through the sether accord- 

 ing to general physical laws, in the manner required to 

 constitute the physical cosmos, but that there may also 

 be a closer interpenetration of atomic nuclei in which far 

 more complex agencies -are involved. 



The mechanical atom of the earlier physicists, con- 

 sidered in this physical aspect, as an unknown core deter- 

 mining the field of activity in the surrounding sther, has 

 had, since Faraday's discoveries in electrolysis, to take on 

 a more definite form as the electrical atom. The result 

 had been fully reached by Faraday himself, though it 

 needed to be enforced later by Helmholtz, that the energies 

 which hrive play in chemical combination are of electrical 

 origin, implying thereby, according to Maxwell's inter- 

 pretation, energies of intrinsic stress and motion brought 

 to bear from atomic stores located in the adjacent a;ther. 

 This doctrine has led on to the modern theory of purely 

 electric atoms, which was already demonstrable on 

 theoretical grounds, of course in a way less definite than 

 we now know it, before the very remarkable discovery of 

 electrons actually free had been reached, through the 

 phenomena of radio-activity either electrically induced or 

 spontaneous. Here again there is the same choice of 

 points of view open to t^-ntative development. We may 

 proceed on a limited hypolhesis as if the electrons are the 

 sole primordial atoms ; or we may assume that there are 

 .•arious ultimate atoms which have existence and structure 

 of their own, of tvpe largely unknown and independent of 

 the aither, and that the electrons which are associated 

 with them, whether temporarily or intrinsically, form 

 merely one feature of their constitution, viz. their means 

 of communication with the a'thcr, and through it with 

 other atoms at a distance to form an ordered universe. 



In anv case we are right in following out the hypo- 

 lhesis, there being, in fact, none other open to us, that 

 the purely physical manifestations of atoms — those, namely, 

 that, owing to the simple interconnection involved in their 

 common seat in the sether, aggregate into the definite 

 physical qualities of matter in bulk — are in the main or 

 in most circumstances practically a group by thi'mselves, 

 and that they are thus caoable of being investigatr'd on 

 these broad, simple principles of dynamics, which Newton 

 definitely formulated as a suitable foundation for the 

 analysis of general physical activity, as it presents itself 



NO. 2002, VOL. 77] 



in the universe. This so-called mechanical hypothesis has 

 been eminently the fruitful one ; it pointed the way to the 

 principle of the conservation of energy, and is now 

 elucidating the wider principle of its definitely limited 

 availability ; it gave a rational explanation of the spec- 

 trum and of radiation in general, which has proved a 

 trustworthy and precise guide to investigation of pheno- 

 mena far below the surface, such as the selective dis- 

 persion of light and the magnetic action on radiation ; it 

 reduced electrical phenomena to order and control, and 

 connected them with light. It must therefore be presumed 

 to be available as the clue for the further elucidation of 

 pressing problems, such as the nature of the transmission 

 of gravitation and of the intimate operation of chemical 

 affinities. 



The tendency to reject dynamical analysis as artificial 

 in such subjects as electrodynamics, which received some 

 stimulus from the theoretical writings of Hertz, seems to 

 overlook the fact that it was precisely as a compact work- 

 ing basis suitable for the formulation of experience in its 

 more general aspects that the Newtonian scheme of 

 dynamics was put forward by its author. In the course 

 of time that scheme has become wider and more elastic 

 through the generalisations of Lagrange and Hamilton, 

 expounded forcibly on the physical side by Kelvin, Helm- 

 holtz, and various others. But to take over the final 

 results, and dress them in new language devoid of the 

 dynamical implication, seems to involve a misreading of 

 scientific evolution. 



This position may be' enforced by a quotation from the 

 final exposition of Newton's views on the scope of natural 

 philosophy in general, inserted by himself at the end of 

 the famous "Queries," in " Opticks," ed. 3, p. 377: — 

 " To tell us that every Species of Things is endow 'd with 

 an occult specifick Quality by which it acts and produces 

 manifest Effects, is "to tell us nothing : But to derive two 

 or three general Principles of Motion from Phaenomena, 

 and afterwards to tell us how the Properties and Actions 

 of all corporeal Things follow from those manifest Prin- 

 ciples, would be a very great step in Philosophy, though 

 the Causes of those Principles were not yet discovered : 

 .^nd therefore I scruple not to propose the Principles of 

 Motion above mention 'd, they being of very general Extent, 

 and leave their Causes to be found out." Then he proceeds 

 to associate his laws of motion with an atomic theory. 



A review of the electrical side of the atomic theory 

 requires a consideration of the phenomena of ionisation in 

 solutions. The theoretical difficulties which have presented 

 themselves in this subject were discussed, in particular 

 the nature of the energy changes which must occur when 

 a salt is dissolved and thus split into separate ions. 

 Reasoning from the processes of the voltaic cell, as ex- 

 pounded after Faraday by Helmholtz, the view is advanced 

 that an equivalent of purely local potential energy of 

 affinity with the solvent must be exhausted in order to 

 provide for the separation of the ions, but without much 

 violent motional disturbance such as would diffuse partially 

 away into the form of heat. This absence of such motional 

 dissipation of the energies of affinity, as indicated, for 

 example, by their almost complete mechanical availability 

 in a Danieil's cell, is perhaps connected with the intimate 

 contacts in confined spaces which are characteristic of the 

 processes at the electrodes by which the chemical change 

 is effected. It is suggested that a similar mode of ex- 

 planation applies to the very hjgh, sometimes nearly 

 complete, mechanical availability (Berthelot) of the energy 

 of chemical transformations in dense media such as liquids 

 and .solids, as contrasted with dilute systems such as gases, 

 which the recent work of Ncrnst and his pupils has 

 brought again to the front. 



The lecture passes on to touch on those extensive 

 branches of chemical physics to which the constitution of 

 the atom is not essential, where only a statistical grasp 

 of the molecular associations and dissociations that are 

 taking place is required. The quantitative theory of 

 chemical equilibrium and of progress of chemical change 

 as regards dilute systems comes under this head, of which 

 the prototype and" the most highly developed example is 

 the kinetic theory of gases. The modern theory of electro- 

 dynamics, as based on the disolacements and motions of 

 electrons,' is in the main analogous, and the theory of 



