Supplement to ''Nature^' May 5, 1904 



to the material bodies around us ? or may we assign to 

 It a constitution of its own, to be tested by its success 

 in comprehending the complex of known relations of 

 physical systems ? This is not the occasion to follow 

 up that question. It would appear that Lord Kelvin 

 •cannot grant that such a constitution has been deter- 

 mined until it has made clear in full detail the mode 

 of connection of the atom with the a?ther, so that a 

 precise mechanical model of it could be imagined; 

 whereas, on the other side, it may be held to be the 

 merit of the scheme that it evades such a hopeless task. 

 :and defines physics as relating to the surrounding field 

 •of EBthereal activity of the molecules rather than to 

 the molecules themselves, which must remain in many 

 respects inscrutable — a consummation that would 

 hardly have been attempted had not the illuminating 

 ■conception of Lord Kelvin's vortex-atoms shown the way. 



The plan along which Lord Kelvin now finds it 

 most hopeful to pursue ultimate physical synthesis 

 .admits the existence of " electrions," freely mobile 

 through Eether simply because two media can be super- 

 posed indcpendentlv in the same space, which exert 

 <lirect ]orcc at a distance upon the asther as also does 

 the matter itself, that the forces are so enoi-mous as 

 sensibly to compress or expand the aether around these 

 nuclei, and that the source of electric, chemical and 

 ■elastic action is thus to be found. This conception is 

 developed over many pages with the power and con- 

 ciseness that are familiar to his readers; it remains a 

 question for the future whether it will prove to be a 

 fruitful theory ; it certainlv forciblv illustrates manv 

 <leep molecular phenomena, and demands, and will 

 doubtless receive, very careful study. 



The iKiint of view is illustrated in p. joo, in treating 

 of the spheres of activity of the various kinds of mole- 

 cules, where Lord Kelvin states that this " is a most 

 interesting subject for molecular speculation, though 

 it or any other truth in nature is to be explained by a 

 proper law of force according to the Boscovichian 

 doctrine which we all now accept (many of us without 

 knowing what we do) as the fundamental hypothesis 

 •of physics and chemistry." ^^'hen one reflects that to 

 Lord Kelvin, more than to an\one else except Faradav, 

 has been due the stimulus to replace artificial mathe- 

 matical attractions by activity propagated according to 

 simple relations, this sentence may perhaps be taken 

 as expressing his belief that in probing into the details 

 of the dynamics of the unexplored molecules we are 

 •still practically confined to the partial but fruitful con- 

 ception of mutual forces. 



Thus in the appendix entitled " .\epinus .\tomized,"' 

 a definite foundation is postulated by taking the elec- 

 trion to be a very minute negative ionic charge, and 

 an atom to involve a positive ionic charge rigidly dis- 

 tributed through a much larger sphere, but in normal 

 condition neutralised by one or more electrions inside 

 it, which may be occasionally shot out as kathode rays ; 

 and electrions and atoms can be wholly or partially 

 superposed in- the same space without mutual deform- 

 ation. On this basis the statical configurations of elec- 

 trions in the spheres, that can represent neutral atoms, 

 are discussed and are applied to the dielectric quality of 

 matter and its aeolotropy in crystals, to the intricate 



NO. 1801, VOL. 70] 



and elegant details of the pyroelectric and piezoelectric 

 quality in the latter, and in more general terms to the 

 nature of conduction and its striking relation to 

 temperature, so different in pure metals and in non- 

 metals and alloys. In further appendices the same 

 conception is applied to crystalline dynamics, where 

 auxiliary Boscovichian laws of pure attraction are also 

 introduced, because Lord Kelvin thinks a purely 

 electric basis is too narrow, even when not restricted 

 to spherical nuclei as here. The whole is developed on 

 all sides with marvellous directness and facility in 

 tracing out crystalline gtoupings in space, which, how- 

 ever, make it difficult reading, though relieved by fre- 

 quent flashes when ,-i vivid analogue of some ascer- 

 tained experimental relation appears. It is a concep- 

 tion such as this that Lord Kelvin has in mind in his 

 postulate, above referred to, that material bodies are 

 labile to optical compressional waves. The free 

 molecular vibrations that must correspond to a bright 

 line-spectrum do not come in for consideration ; nor 

 does the now burning question of actual dissociation 

 in typical chemical atoms. 



The task of making a review of a book like the pre- 

 sent one can at best be very imperfectly executed. The 

 book is largely a new creation. It surveys a vast 

 range, all the cognate subjects on which the author 

 feels that he has something new to communicate — laws 

 of diffusion of gases, transparency of the sky, detailed 

 dynamics of optical chirality, motion of molecules 

 through aether, front of a wave-train in a dispersive 

 medium, the finiteness of the universe, atomic theory 

 of electricity, regelation and plasticity of ice, waves 

 and ripples on water and their dispersion, crystalline 

 structure and iridescence, partition of energy in 

 molecular systems, crystalline dynamics on Boscovich's 

 principles, electric and magnetic screens. Instead of 

 putting the question. Is this subject clearly and 

 strikingly expounded? one has rather to ask. Is this 

 new departure or revolutionary idea justified by its 

 results? Any off-hand decision is, of course, im- 

 possible. When one is in difficulty over inscrutable 

 or irreconcilable phenomena, it will be a book to turn 

 over to see what the premier authority has to say on 

 the subject in hand ; for what he says is not lightly 

 thrown from his pen. it is the work of twenty years, 

 and withal it forms a consistent whole. In the re- 

 marks here made about only a few of the many themes 

 of which it treats, it is the obviously revolutionary 

 element that has attracted attention. There is, how- 

 ever, one very serious criticism as to which there can 

 be no question. This book of seven hundred pages — 

 dealing in concise manner with nearly all the most 

 intricate topics of dynamical and molecular theory, 

 with the cross references and recurrences to previous 

 passages that are involved in twenty years of prepar- 

 ation — is without an index, and the detailed table of 

 contents does not meet the want. The thanks of the 

 scientific world will surely go to the veteran author, 

 now by a happy choice Chancellor of the university 

 which he has so long adorned, for this splendid gift, 

 which stimulates and educates even where it tails to 

 convince, and bears on every page evidence of 

 profound and unwearying thought. J. L. 



