420 



THE POPULAR SCIENCE MONTHLY, 



are eituated upon one of the cnrvee which ca"n 

 he drawn in each section of the rinij, are indis- 

 solubly tied down to their circular paths, and 

 can never quit them ; so that the whole mass of 

 the vortex ring will be always formed of the 

 same particles. This theorem was proved by 

 Helmholtz in 1858. This eminent physicist has 

 analyzed the vortex motions which would exist 

 in a perfect fluid free from all friction. He has 

 proved that in such a medium vortex rings, 

 hounded by a system of vortex liues,* are formed 

 of an invariable quantity of the same liquid mol- 

 ecules, so that the rings can move, and even 

 change their form, without the connection of 

 their constituent parts ever being broken. 

 They will continue to revolve, and nothing will 

 be able to separate them, divide them, or de- 

 stroy them. Those existing in the liquid will 

 exist there for ever, and new ones can only be 

 excited in it by a creative act. 



The smoke-rings, of which we have spoken 

 above, would give a perfect representation of 

 these liquid vortex rings if they were formed 

 and moved in a perfect fluid. They are not so ; 

 but such as can be formed can serve for the 

 demonstration of some properties of matter in 

 vortex motion. They are eudowed with elasti- 

 city and can change their form. The circle is 

 their position of equilibrium, and, when their 

 form is altered, they oscillate round this posi- 

 tion, aud finally rcassume the circular form. 

 But, if we try to cut them, they recede before the 

 knife, or bend round it, without allowing them- 

 selves to be injured. They give, therefore, a 

 representation of something which would be in- 

 divisible. And when two rings meet each other, 

 they behave like two solid elastic bodies ; after 

 the impact they vibrate energetically. It is a 

 singular fact that when two rings are moving in 

 the same direction, so that their centers are 

 Hituated upon the same line, and their planes 

 perpendicular to this line, the hinder ring con- 

 tracts continually, while its velocity increases ; 

 the ring in advance, on the contrary, expands, 

 and its velocity decreases until the other has 

 passed it, when the same action recommences, 

 so that the rings alternately pass through each 

 other. But, through all these changes of form 

 and velocity, each preserves its own individu- 

 ality, and these two circular masses of smoke 

 move through the air as if they were something 

 perfectly distinct and independent. These curi- 

 ous experiments were made in England. t 



Helmholtz, therefore, has discovered the fun- 

 damental properties of matter in vortex motion, 

 and Sir William Thomson has stated, "This 

 perfect medium and these vortex rings which 

 move through it, represent the universe." A 

 fl'iid fills all space, and what we call matter are 

 portions of this fluid which are animated with 

 vortex motion. There are innumerable legions 

 of very small fractions or portions, but each of 

 these portions is perfectly limited, distinct from 

 the entire mass, and distinct from all others, 



* " Wirbelfaden nnd Wirbellinien." 

 t P. G. Tait. " Lectures on some Recent Ad- 

 vances in Physical Science." London, 1876. 



not only in its own Bubstance, but in its mass 

 and its mode of motion qualities which it will 

 preserve for ever. These portions are atoms. 

 In the perfect medium which contains them all, 

 none of them can change or disappear, none of 

 them can be formed spontaneously. Every- 

 where atoms of the same kind are constituted 

 after the same fashion, and are endowed with 

 the same properties. It is well known, in fact, 

 that the atoms of hydrogen vibrate exactly in 

 the same periods, whether we heat them in a 

 Geissler's tube, observe them in the sun, or in 

 the most distant nebulas. 



Such is, in a few words, the conception of 

 vortex atoms. It accounts, in a satisfactory 

 manner, for some properties of matter, and of 

 all the hypotheses upon the nature of atoms it 

 appears to be the most probable. We see also 

 that it permits the revival of the ancient hypoth- 

 esis of the unity of matter, and in a more ac- 

 ceptable form than that of Prout's hypothesis. 

 Is the idea absolutely new ? No ; it was origi- 

 nally conceived by Descartes. So far is it true 

 that, when the perpetual, and perhaps insolv- 

 able, problem of the constitution of matter is 

 discussed, the human mind seems to turn in a 

 circle, the same ideas lasting for ages, and being 

 presented under fresh forms to the highest 

 intellects who have endeavored to solve this 

 problem But is there no diflerence among these 

 great intellects in their manner of working? 

 Most certainly: some, more powerful, perhaps, 

 but bolder, have proceeded by intuition ; others, 

 better armed and stricter, by Induction. Here 

 lies the progress and the superiority of modem 

 methods, and it would be unjust to pretend that 

 the important eflforts, of which we have had 

 striking testimony, have not made an advance 

 in this difficult problem which was impossible 

 to Lucretius and even to Descartes. 



The Skin in Health and Disease. By L. 

 Duncan Bclkley, M. D. Philadelphia : 

 Presley Blakiston. Pp. 148. Price, 50 

 cents. 



We have here an excellent contribution 

 to the series of " American Health Primers." 

 It is as good as its predecessors, which is no 

 slight praise. There are many popular books 

 on that important subject, " The Skin," and 

 several of them meritorious, but this is no 

 reason why Dr. Bulkley should not have 

 made another because, in the first place, 

 this interesting organ of the body is very im- 

 portant in relation to health, and there are 

 but few people who are at all aware of it. 

 They have not only to be taught, but the les- 

 sons must be hammered into them by cease- 

 less repetition. Hence the need of fresh 

 and unremitting inculcations. Dr. Bulkley's 

 book is to be welcomed on this ground ; but 

 it has also a special merit which we have 



