SCIENCE. 



20T 



Whether or not the relation — = holds in any 



particular case can, it would seem, be determined only by 

 experiment. So, too, the fact of the equal absolute 

 energy of vibration of two atcms. Our experimental 

 methods are, however, as yet far from competent to deal 

 with either question, and until they are it is certainly pre- 

 mature to build up speculative hypotheses. 



Every student cf molecular science knows how great is 

 the temptation to build hypotheses which are to account 

 for all the physical and chemical relations of mat- 

 ter. We can read between the lines of nearly all 

 our recent writers in this department of science their 

 secret belief that chemical phenomena are probably but a 

 complex phase of mechanical phenomena, and that all 

 matter is probably one. Nor are facts justifying such 

 views altogether wanting. Probably no chemist would 

 be bold enough to say in how far such phenomena as, for 

 instance, the solution of ammonia, carben dioxide, and 

 many other gases in water are of purely chemical and 

 how far of purely physical nature. There are many 

 other phenomena in which similar difficulty wculd be 

 felt. The phenomena of adhesion and cohesion are such 

 that it does not require a very great stretch of the imag- 

 ination to suppose that they may be but different phases 

 of what we call chemical union. But to pass from such 

 general and indefinite speculations to suppositions in re- 

 gard to the mechanical conditions which will account for 

 all these phenomena and all the properties of matter upon 

 purely mechanical principles is a long and, indeed, a bold 

 stride. As the temptation to make this attempt is great, 

 so ought our caution to be great in making the attempt. 

 Professor Dolbear's immediate predecessor in this at- 

 tempt is Professor Norton. His hypothesis of two atmos- 

 pheres, one attractive, the other repellant, surrounding 

 each atom, is too artificial, and in being in opposition to 

 the " Kinetic Theory of Gases," is probably too much out 

 of sympathy with the tendency of modern thought to 

 make many converts. Not so, however, with Professor 

 Dolbear's speculations. Their great fundamental sim- 

 plicity, as well as their thoroughly Kinetic nature, make 

 them dangerous to healthy progress in molecular science 

 unless they can maintain their right of being by account- 

 ing for at least the chief and fundamental phenomena of 

 matter. I shall now attempt to apply the touch-stone to 

 them. In Section IV. of his first paper Professor Dolbear 

 advances an hypothesis of chemical union founded on the 

 analogy to a vibrating body which, as is well known by 

 reducing the average density of the atmosphere, 

 causes light bodies to cling to it by atmospheric 

 pressure. We are told that precisely the same con- 

 ditions exist in the ether near a vibrating atom ; 

 that the average density of the surrounding ether is less- 

 ened, and that by extraneous pressure another atom vi- 

 brating synchronously with the first would attach itself 

 thereto, and the molecule would be formed, etc., ^etc. 

 I would like to ask how Prof. Dolbear can consistently 

 speak of the density of ether, which, he says, is not mat- 

 ter. Now, in this idea of density there is implicitly the 

 idea of mass, for density, as every one knows, is the mass 

 or amount of matter in unit volume. But, disregarding 

 this inconsistency, it is certainly very bold induction, if 

 induction it can be called, to attribute chemical union to 

 a lessening of density of ether due to atomic vibrations 

 because a vibrating tuning-fork attracts light bodies 

 when brought sufficiently near. In the professor's hy- 

 pothesis the atoms (vortex-rings) vibrate about a circle 

 as figure of equilibrium, and consequently have four 

 points of maximum displacement or minimum density of 

 the ether. As a consequence of this, each atom must 

 attract other atoms capable of attaching themselves to it 

 at four points. To judge from his diagrams, the Profes- 

 sor believes that atoms unite only in two-dimensional 

 space, i.e., that the centres of all the atoms lie in the same 

 plane. Such a distribution of the atoms would render 



any closed structure such as a saturated molecule an 

 impossibility, for the peripheral atoms would constantly 

 attract further atcms as long as they vibrate, and other 

 atoms vibrating synchromcally w ith them aie present. If, 

 on the other hand, the atoms are arranged in tri-dimen- 

 sional space, having their centres in planes, say, at right 

 angles to oneancther, the simplest molecule and the only 

 really stable one would have to contain six atoms whose 

 planes of rotation form the faces of a cube. A further 

 possible supposition is that the atoms would arrange 

 themselves in parallel planes with their centres in a line 

 at right angles to these planes. The first of these sup- 

 positions, as already indicated, would not allow the 

 formation of saturated molecules, and it would seem that 

 all chemical union, as we krow it, could not exist, for it 

 would evidently be altogether a matter of chance how 

 atcms grouped themselves in regard to numbers, so 

 that we could not always obtain like results of 

 union under precisely like conditions. The second sup- 

 position is also inconsistent with chemical facts, for we 

 have molecules of two, three, four and five atoms, 

 as well as others containing hundreds. The third 

 supposition is also untenable, for from Helmholtz's math- 

 ematical investigations and Tait's experiments we know- 

 that two vortex-rings, when they move axially in the same 

 direction alternately, pass through each otherone expand- 

 ing, the other contracting, while when moving axially in 

 opposite directions they both expand movirg slower and 

 slower, but never meet. This is, according toTait, about 

 all we know experimentally or mathematically in regard 

 to the action of one vortex ring upon another. It is cer- 

 tainly a little strange that Prof. Dolbear, in framing his 

 hypothesis, completely ignores these known facts, and re- 

 lies on a far-fetched analogy. Serious as are these diffi- 

 culties, they are by no means the most serious. If experi- 

 mental evidence is worth anything, we must believe that 

 elementary molecules, with a few exceptions, consist of two 

 atoms, which are, as faras we can judge, exactly alike. Fur- 

 thermore, we find that in all chemical reactions we can 

 deal with nothing less than the molecule ; we know and 

 can deal with the atom only as a part of a molecule, and 

 not as an independent existence. When chemical union 

 takes place between two elements, there is simply an in- 

 terchange of atoms between the molecules. The differ- 

 ence between the molecules of an element, and those of 

 a compound, is simply this, that the atoms of elementary 

 molecules are all alike, while those of a coin- 

 pound molecule are unlike. I repeat all these funda- 

 mental and well-known chemical facts and deductions, to 

 show how singularly inadequate Prof. Dolbear's hypothe- 

 sis is to account for even the most simple chemical facts. 

 Accordmg to his hypothesis, the atoms whose rates of vi- 

 bration are most exactly alike, must form the most stable 

 molecules. Consequently, the atoms of an element must 

 cling more firmly together than can those of two different 

 elements, and chemical union between the elements be- 

 comes impossible. Did the atoms of elements exist as indi- 

 viduals, and not as parts of molecules simply, synchronism 

 of vibrations might be a possible supposition to account 

 for chemical union ; but as the case stands, we must re- 

 ject any such hypothesis as precluding all combination 

 between atoms of different elements. Setting aside even 

 this difficulty, how are we to account by synchronous 

 vibrations for the liberation of energy in the form 

 of heat and light, which accompanies most chemi- 

 cal unions. These forms of energy are, according 

 to the Professor himself, altogether due to vibra* 

 tions of the atoms and these same vibrations 

 cause the union. Now, how can they both cause the union 

 and be produced by it? Does ihis not look a little like 

 per ficluum mobile? Had the Professor tried to explain 

 adhesion and cohesion by molecular vibration his posi- 

 tion would undoubtedly be much stronger. We know 

 that molecules are complex and that there must be 

 motion of their parts relative to the centre of mass of 



