S5 



NATURE 



{_May 20, 1880 



as it does with the mere rotation of a portion of matter.' 

 It is so far recognised that simplicity of the means to 

 the end is a general characteristic of nature. No doubt 

 there maybe difficulties in the mathematical development 

 of the subject ; but if an atom be once proved to be 

 elastic and indestructible, that fact surely goes very far 

 10 supply all we want for the practical applications of the 

 theor>-. Of course there may be some refinements that 

 may present great mathematical difficulties. For instance, 

 Prof. Tait in his work, " Lectures on some Recent Ad- 

 vances in Physical Science," mentions a case where a 

 vortex-ring is supposed to come into collision with 

 another in such a way that the motion is not symmetrical 

 in relation to the axis, and it is cited as an almost insur- 

 mountable difficulty to find what exactly takes place (in 

 regard to particular vibrations or rotations developed, 

 possibly). But one might ask, is it necessary to know 

 this for practical problems of physics ? We may know 

 broadly that vibration or rotation is developed, and if so 

 (apart from the abstract interest of the question), do we 

 want to know precise quantitative details for practical 

 purposes ? It might for example be extremely difficult 

 to determine mathematically the exact deformation or 

 changes of form (vibrations, &c.) that a steel ring under- 

 went when thrown against the hard surface of an anvil ; 

 but the practical question is, do we want to be acquainted 

 with this for any ordinary problem that might occur, or in 

 order to appreciate the general principles of impact, for 

 instance.? So in the case of vortex-atoms, no doubt 

 many instances might be cited when it would be difficult 

 to ascertain precise results, but the practical question is. 

 Does this prevent our applying the theory to ordinary 

 physical problems,- or to dynamical phenomena involving 

 questions of principle.' For possibly it may not be 

 necessary to know the exact vibrations developed at a 

 collision (for instance), provided we recognise the funda- 

 mental point that energy is conserved, and that the atoms 

 can rebound from each other like perfectly elastic solids. 

 It would be a pity if the mere difficulty of arriving at 

 precise mathematical results of a refined character, should 

 be mistaken by some for mystery, or it would be a thing 

 to be regretted if there should be any tendency to throw 

 a veil of the " occult " over what in its physical basis (at 

 least) is very simple, this procedure only hindering pro- 

 gress and rendering a closed book what might be a most 

 interesting branch of mechanics. 



The investigations regarding the perfect liquid have 

 already (as is known) thrown some important light on the 

 important practical question of the resistance of ships. 

 Mr. Froude has especially devoted himself to these 

 mquiries. The old idea that a ship (or more correctly a 



' It would seem to be thought by some that the primary ring f irm r,f t'-e 

 vortex-atom mvolves something complicated in it. I venture to think tdat 

 tms IS only one of those first impressions, which will disappear on reflecting 

 on the subject. Fu-st, many facts strongly indicate that matter possesses a 

 more or less rtfen structure (or is highly p tous). These ring molecules 

 would give matter an c pen structure. It would seem also independently 

 probable that a molecule should have no more material in it than is essential 

 to give It a certain amount of extension, or to make it occupy a certain range 

 of space. Why should we suppose that waste or apparent superfluity of 

 material in a molecule that a solid structure throughout would involve ? 

 Does not this violate one of the fundamental principles of large scale archi- 

 tecture, where supei lluity of material is recognised as one cf the worst faults, 

 and mechanical princip es are admittedly independent of scale t The ring shape 

 for the atom is evidently the simplest elementary form to satisfy the condition 

 tor the maximum oi c.rtensioii combined w.th the minimum waste or expendi- 

 ture of material. In view of these consideralions. the ring-shape, the primary 

 form requu-ed by the vorte.vatom theory, may seem in itself independently 

 probable. Indeed, it seems a remarkable fact that the main cond tions in 

 evitably led up to by this theory by a rigid mathematical process, are pre- 

 cisely those that independent observations support, (i) the indestructibility 

 of the atom, illu'trated by chemistry and numerous facts, (2) the elasticity 

 or tne atom, proved by the spectroscope, (q) the ofen structure of the atom 

 m harmony with the transparency of some bodies to light, the free passage of 

 the magnetic disturbance through all bodies, and numerous other facts-net 

 10 mention the phy.ical theory of gravity. In short, it would appear that it 

 ■would be necessary to infer the existence of indestructible elastic atoms 

 of open structure, even if the vortex atom theory (which explains this fact) 



h ad not been invented. j^ r , 



= The writer himself has .seen from German comments on Prof. Tait's 



work, that the passage above referred to [German translation] has been 



regarded by some as if the difficulty there mentioned were of such a nature 



•as to prevent the practical adopt.on of the theory. 



totally immersed body, ^such as a fish) encountered a 

 mysterious resistance in addition to the mere friction of 

 the molecules of water on its sides, is now known to have 

 been a pure delusion. If it were not for the fact that the 

 water consisted of molecules or ultimate rigid parts which 

 are caught and put in motion by the rough sides of the 

 ship, there would be demonstrably no resistance at all. 

 Hence the absence of resistance in a true liquid (which is 

 not formed of ultimate rigid parts or molecules). If the 

 molecules or ultimate rigid parts of which an ordinary 

 "liquid" consists, were to be liquefied, a being immersed 

 in it would (if conscious) imagine he was surrounded by 

 empty space. 



The late Prof. Clerk Maxwell in a review of the theory 

 of vortex-atoms in the "Encyclopedia Britannica " for 

 1875, under the word '^ Atom," makes the following 

 remark on the theory : — 



" But the greatest recommendation of this theory from 

 a philosophical point of view, is that its success in 

 explaining phenomena does not depend on the ingenuity 

 with which its contrivers ' save appearances ' by intro- 

 ducing first one hypothetical force and then another. 

 When the vortex-atom is once set in motion, all its 

 properties are absolutely fixed and determined by the 

 laws of motion of the primitive fluid, which are fully 

 expressed in the fundamental equations. The disciple of 

 Lucretius may cut and carve his solid atoms in the hope 

 of getting them to combine into worlds ; the follower ot 

 Boscovich may imagine new laws of force to meet the 

 requirements of each new phenomenon ; but he who 

 dares to plant his feet in the path opened out by Helm- 

 holtz and Thomson has no such resources. His primitive 

 fluid has no other properties than inertia, invariable 

 density, and perfect mobility, and the method by which 

 the motion of this fluid is to be traced is pure mathe- 

 matical analysis. The difficulties of this method are 

 enormous, but the glory of surmounting them would be 

 unique" [p. 45]. 



Much misapprehension would seem to exist in regard 

 to the physical side of the theor}', especially in Germany,^ 

 where the mathematical investigations out of which it 

 sprung, had their origin. Some appear to be unable to 

 conceive how motion should take place in a material 

 substance continuously filling space, losing sight of the 

 fact that the liquid outside the atoms plays the part of a 

 void (in so far as it cannot appeal to our senses) — or it is 

 only the atoms that affect our perceptions. Others fail 

 totally to appreciate the simplicity of the physical side of 

 the theory, and seem to think it involves arbitrary 

 postulates, whereas the main peculiarity of the theory is 

 its freedom from positive assumptions, inasmuch as the 

 theory evolves all the properties of matter out of the 

 motion of a material substance, which without this motion 

 has no positive qualities at all, and could not appeal to 

 our senses. The fact seems to be overlooked that if we 

 renounce the occult quality of n'gidity in the atom, we 

 have no other resource than a liquid (i.e., a substance 

 without rigidity). Much of the misunderstanding on the 

 subject may no doubt be due to the scarcity of the literature 

 relatmg to it, and the extreme brevity and absence of 

 detail or attempt to assist the conceptions regarding the 

 physical side of the theory. This want the author him- 

 self has much felt, and having been at considerable 

 trouble to render clear his own conceptions as far as he 

 could, he has thought that the result of this analysis might 

 not perhaps be unacceptable in the form of a paper on 

 the physical aspects of the theory.- For there are no doubt 



' The writer has had personal experience <f this, partly through corre- 

 spondence, and partly through the literature relating to the subject. Quota- 

 tions from the writings of Prof. Zollner especially seem to show a want of 

 appreciation of the physical pjints of the theory at their true value and 

 significance. 



' As regards sources of info mation as to the vortex-atom theory, the 

 following maybe mentioned. Sir William 'I'homson, "On Vortex-Atoms," 

 Phil. Mag., July, 1867. Prof. Clerk-Maxwell, article "Atom," titcyc. 

 Brit. 1875. The theory is dealt with to some extent in a popular manner ia 



