202 



SCIENCE. 



the molecule. As theie is no good reason for supposing 

 the motions of these parts or atcms to be rather in. one 

 plane than another, we must admit the possibility of 

 motion in all planes. The vibrations would, however, 

 probably be in three planes at right argles to one 

 another in all molecules cf more than three atoms ; and 

 would, consequently, have six points of maximum dis- 

 placement and minimum density of the surrounding 

 ether. Molecules of two and three atoms might possibly 

 vibrate in two cr only one plane. As molecules are net 

 vortex-rings, though possibly groups of vortex-rings, the 

 analogy to a vibrating tunirg fork becomes much closer 

 than in the case of a vibrating vortex-ring, ar.d we are 

 much more justified in iryirg to make application of the 

 hypothesis. Prof. Dolbear's analogy thus modified can, 

 I think, be made a very fair working hypothesis to ex- 

 plain adhesion, cohesion and even crystallization. The 

 phenomena cf surface tension cf l : quids ar.d capillary 

 actic n find a reasonably fair explanation upon this hy- 

 pothesis, and possibly also these of osmosis, dialysis and 

 occlusion. But even here such an hypothesis meets with 

 many difficulties and we must exercise extreme caution, 

 and must gather further experimental evidence before 

 committing ourselves to its acceptar.ee. 



In his second paper the Professor tells us that the vor- 

 tex-ring theory assumes that matter is a form of energy, 

 etc. Never having been so fortunate as to have had 

 access to Sir William Thomson's onginal memoir, I 

 know his celebrated hypothesis only thrc ugh interpreta- 

 tions of others. From these interpretations I have al- 

 ways supposed that this hypothesis assumes that all 

 matter is essentially one ; and that the elements, as we 

 know them, are portions of this common matter imbued 

 with vortex-motion, thus forming vortex-rings variously 

 knotted, whose energy is non-intei changeable with other 

 forms of energy provided the vortex-rings are fcrmed and 

 exist in a perfect or frictionless fluid. If the fluid is not 

 quite perfect, not quite frictionless, the vortex-rings 

 must gradually be destroyed and their energy must be 

 transformed. The uniform material substratum, if I 

 understand the hypothesis correctly, consists of smaller 

 and simpler vortex-rings which are also the particles or 

 atoms of the ether. If, then, I comprehend the positions, 

 the non-transformabihty of the energy of the vortex 

 atoms and also their permanence, i. e. the persistence of 

 our elements depend upon the perfect fluidity of the 

 ether. Whether the ether is perfectly frictionless cr not 

 science is. I think, hardly ready to answer. To call 

 "matter a form of energy not. interchangeable with other 

 variable forms" is, under the circumstances and from the 

 meaning of the terms employed, to take extraordinary 

 liberties with language. Physically regarded, energy is, to 

 strip the term of all technicalities, matter in motion. Then 

 Professor Dolbear's statement becomes matter, is a form 

 of matter in motion, which is hardly intelligible. Again 

 we are told ' The energy of a mass of matter varies as 

 the square of the velocities, but the properties of the 

 mass vary with the fcrm of the energy, that is to say the 

 physical properties of a heated body are not identical 

 with those of the same body when it is cool, but pos- 

 sesses the same amount of energy in free path motion." 

 Exactly what this sentence means is, I must confess, be- 

 yond my comprehension. One thing, however, seems 

 certain, that it expresses an idea directly opposed to the 

 " Mechanical Theory of Heat " and the " Kinetic Theory 

 of Gases" in the statement that a cool body " possesses 

 the same amount of energy in free path motion " as the 

 same body when heated. If this be so, what becomes of 



v P — v ft for gases, and what of the " Thermo-dynamic 



T f 



Scale of Temperature." 



In regard to the assumption — = atomic weight and 

 the calculations based thereon, I will merely remark that if 



the groups having the same m or those having the same 

 v showed any family likeness or any gradual variation cf 

 pioperties as do Mendelej( ff's periocsand grcups ; then 

 they wculd be worthy of censideraticn. As it is, how- 

 ever, they seem rrere juggleiy with figures. That 

 the atcms of the elements have a " commonform differing 

 aiithmetically from each other in size and velocity " is 

 utterly inconsistent with the well-known facts and phe- 

 nomena of quantivaler.ee or valency of atcms. There 

 wculd have to be two forms at least one for aitiad, and 

 cne for perissad atoms. I think for the present, at least, 

 we must reject this idea of simplicity and still follow Sir 

 W illiam Thomson. 



In the thiid paper we read, "There is now sufficient 

 evidence for the belief that the Kinetic energy of atcms 

 and molecules consists of two parts, one of which is the 

 energy of .translation or free path, the other cf a change 

 of form due to vibrations of the parts of the atom ormole- 

 cule toward or away frcm its centre of mass. The pres- 

 sure of a gas is immediately clue to the former while the 

 temperature depends solely upen the latter." To the first 

 sentence of this quotation I object, because atcms and 

 molecules are treated as if similar, for w T hich assumption 

 we have no evidence. The second sentence contains the 

 very strange idea that the temperature of a gas is duecnly 

 to the internal energy of the molecule. Maxwell in his 

 " Theory of Heat " Chap. XXII, under " Specific Heat at 

 Constant Volume " says : " Since the product pv is propor- 

 tional to the absolute temperature, the energy is propor- 

 tional to the temperature." By energy Maxwell here 

 means, as appears frcm the context, what Prof. Dolbear 

 would call total energy. From this it appears that Prof. 

 Dolbear's statement can hardly be correct. If we le- 

 member that Maxwell speaks of molecules and Prof. Dol- 

 bear of atoms the latter's statement becomes still more 

 doubtful. The assumption that "these two forms of energy 

 must indeed be equal to each other in a gasunder uniform 

 conditions," upon which all the Professor's calculations in 

 his third paper are based, can easily be disproved. The 

 Kinetic energy cf agitation of a molecule is y z mv°- and 

 the (total) energy is " }4 P mv' 2 where ft is a factor always 

 greater than unity and probably equal to 1.634 for air 

 and several of the more perfect gases." Hence the in- 

 ternal energy is y z (.634 mv i .) This, of course, inval- 

 idates all the Professor's calcula'ions. 



Having extended my remarks far beyond what I origi- 

 nally intended, I shall touch upon only one more point, 

 though I find various other difficulties in the Professor's 

 speculations. The last paragraph of the third paper be- 

 gins : " As at absolute zero each atom is quite indepen- 

 dent of every other atom, that is, matter has not a 

 molecular structure, etc." Now, I would like to ask the 

 Professor how he knows this. Such a state of affairs 

 would indeed make the absolute zero a more than singu- 

 lar point in the curve cf the properties 01 matter. 



Buffalo, N. Y.. April 20, 1881. Wm. H. Dopp. 



LETTERS TO THE EDITOR. 



[The Editor does ?wt hold himself responsible /or opinions expressed 

 by his correspondents. No notice is taken of anonymous communi- 

 cations^ 



Intra-Mercurial Planets. 

 To the Editor of " Science :" 



I wish to say that in the ske:ch given to "SCIENCE," 

 No. 35, p. 95, the position of Professor Swift's Vulcans 

 is very nearly as they were put down by Professor 

 Swift himself on a map that now hangs in my room at 

 the Naval Observatory. 



As to negative evidence there is somethirg to be said 

 on both sides of the question. When extraordinary dis- 

 coveries are reported they are to be severely examined 

 and carefully criticised. If the observations on which 



