May 20, 1880] 



NATURE 



57 



We shall simply state the facts of the mathematical 

 analysis here, our business being more particularly with 

 the physical side of the theory. First it is shown by 

 incontrovertible mathematical proof that a portion of 

 material having the motion above described possesses 

 all the qualities of a solid. It is at the same time 

 "elastic," or capable of changes of form when acted on 

 through impact by other atoms — always tending to return 

 to its symmetrical form when removed from constraint. It 

 is, moreover, proved to be competent to execute vibrations 

 of definite periods which it is the function of the spectro- 

 scope to measure. The atom thus constituted is demon- 

 strated to be incapable of being divided or severed by the 

 collisions of other similar atoms against it, and since this 

 is the sole means of acting upon it, the long-standing riddle 

 of indestructibility is thus simply solved, without the 

 necessity for any postulate of infinite hardness. As the 

 degree of hardness merely depends on the velocity of 

 rotation of the material, it follows that the vortex-atom 

 may possess any degree of hardness. Indeed, if we 

 imagine the atom to be magnified up to visible scale, it 

 might be conceived to be harder or more rigid than a 

 ring of steel of the same dimensions, since the hardness 

 of steel is limited by the resistance of the component 

 atoms to displacement. 



The centrifugal tendency of the rotating material of the 

 vortex-atom is controlled by the exterior incompressible 

 liquid, and as there is no friction [there being no ultimate 

 solid parts in the rotating liquid to " catch " against the 

 inclosing fluid walls], the rotating portion therefore glides 

 smoothly over the incompressible liquid that surrounds it 

 like a pipe. Indeed, if we leave out of our conceptions 

 the portion of rotating liquid, then the surrounding liquid 

 actually forms a complete pipe in the form of a closed 

 ring. If the liquid in the pipe were to fly out, a temporary 

 void would be foniied in it, which is impossible in a liquid 

 that already occupies all space. An idea of the resistance 

 of such a rotating portion of material to bending may be 

 got by attempting to deflect a gyroscope or spinning-top. 



In the old idea of infinitely hard atoms there were diffi- 

 culties in forming a satisfactory conception of what took 

 place at the collision of two such atoms or how the re- 

 bound could effect itself (consistently with the conserva- 

 tion of energy). The following difficulty may also be 

 mentioned : — Since two such atoms are supposed to be 

 absolutely hard or unyielding, the area of contact at the 

 collision would necessarily be merely a mathematical 

 point. Now the intensity of a given pressure on a sur- 

 face is inversely as its area ; and accordingly, since the 

 area is here a mathematical point (or infinitely small), the 

 pressure attendant on the collision of the two atoms would 

 require to be infinitely great. It may be a fair question 

 how even an infinitely hard atom is to withstand the 

 disintegrating influence of an zV/z^wz'/i- pressure.' 



In the case of the vortex-atoms they yield somewhat at 

 collision (without change of volume, of course), whereby 

 the encounter takes place over a surface (not a point) ; and 

 they rebound in virtue of their elasticity, due to the 

 motion of the material forming them.- 



There would seem to be a view to a certain extent 

 prevalent that the vortex-atom theory essentially alters 

 the basis of the old-established ideas of solid indestructible 

 atoms surrounded by space in which they can freely move, 

 to which so many have accustomed their conceptions, and 

 worked upon to the successful discovery of new facts, and 

 which ideas, therefore, they might be reluctant to abandon. 

 This step, however, is not required at all. The main pur- 

 pose of the vortex-atom theory is to explain the "elasticity" 



* The fact of two such infinitely hard atoms being stopped in an infinitely 

 short space at collision [for there is by hypothesis no ^rrt^'/m/ yielding] would 

 by itself entail an infinite pressure in addition to the infinite pressure due to 

 touching at a mathematical point. 



^ The rebound of vortex-atoms may be illustrated (as is known) roughly 

 by the rebound of two smoke-rings from each other, or by the rebound of 

 vortex rings in an ordinary (imperfect) liquid. 



of atoms, retaining substantially everj-thing else apper- 

 taining to the old atomic theories, merely removing the 

 unsatisfactory postulate of infinite hardness. For since 

 the perfect liquid (outside the portions of it that form the 

 atoms) opposes no resistance whatever to the passage ot 

 the atoms through it, or it is impossible to act on the 

 exterior liquid, it is therefore in this respect as if a void 

 existed outside the atoms. It is desirable, however, to 

 note that the vortex-atom theory involves essentially the 

 existence of the liquid outside the atoms, which performs 

 important functions, but since this exterior liquid is 

 proved to be incapable of appealing to our senses in any 

 way, it therefore in that respect may be said to play the 

 part of a void. The exterior liquid of the vortex-atom 

 theory corresponds to the void space of the theory of 

 Lucretius. With the above qualification, therefore, it 

 may be allowable, when we are not specially dealing with 

 the problem of the constitution of the atom itself, to leave 

 out of our conceptions the presence of the exterior liquid: 

 that which we call "matter" being the atoms, and not 

 the exterior liquid. In all practical problems of physics, 

 therefore (apart from the problem of the constitution of 

 the atom), we may properly regard the atoms simply as 

 elastic indestructible solids moving freely in space. 

 Moreover, since the motion of rotation of the material of 

 the atom is incapable of transference, and cannot appeal 

 to our senses, and this motion does not in any way alter 

 the position of the atom in space [but it is exactly as if 

 the atom itselfiyitrs at rest] ; we can therefore, if we like, 

 leave this rotatory motion out of our conceptions, merely 

 keeping in view the result produced by the rotation, viz,, 

 the sharply-defined elastic indestructible solid thereby 

 formed. The function of the modern theory is accord- 

 ingly not to destroy the atomic theory of the ancients, but 

 rather to support it, by explaining how such indestructible 

 bodies can exist, without recourse to the unacceptable 

 postulate of infinite hardness. This old theory of the 

 atomic constitution of matter was really too firmly 

 grounded on r-eason and observation, as that one should 

 suppose that its very foundations could be shaken. 



Broadly and generally, therefore, in practical problems of 

 physics, the essential points to recognise are that atoms — 

 or molecules — are elastic indestructible bodies, capable of 

 rebounding from each other w-ithout loss of energy, and of 

 executing vibrations of fixed periods. The existence of 

 this elasticity is a fact so definitely proved by the spec- 

 troscope, which actually measures the number of vibra- 

 tions executed per second by molecules, that it would 

 become a question to explain this fact, even if the vortex- 

 atom theory had not been proved to be capable of 

 affording a complete explanation of it. Indeed, not only 

 is the theory capable of doing this, but the vibrating 

 capacity possessed by molecules is shown to be a necessary 

 consequence of the theory, so that, therefore, the fact 

 might even have been deditced a priori. Considering how 

 enormously difficult it appeared to account for this fact 

 at one time, or how impossible it seemed to reconcile 

 the mobility of the parts of a molecule with the insepara- 

 bility of these parts by the most energetic collisions, and 

 how an explanation of this fact was at one time sought 

 after, it would appear not too much to expect that those 

 who hesitate to accept ihe explanation given by the 

 vortex-atom theory, should endeavour to define for 

 themselves wherein their grounds of objection lie. For 

 if the explanation of a fact be admitted to be substantially 

 complete, it would be at least unreasonable to look for 

 more. The question might also suggest itself as a fitting 

 one to any impartial inquirer, whether any other solution 

 to the problem of the constitution of the atom is m prin- 

 ciple conceivable, or whether [as in the case of many other 

 physical problems, the constitution of the ether, for 

 instance] but one solution is conceivable (or we have no 

 choice at all). It cannot be said at least that the theory 

 of vortex-atoms, or its physical side, is not simple, dealing 



