1^2 



NATURE 



[December 13, 1894 



the acetylene explosion 114. Some experiments I have recently 

 made in conjunction with Mr. J. C. Cain confirm these calcu- 

 lated pressures. When the explosion-wave was propagated 

 through a mixture of equal volumes of cyanogen and oxygen it 

 broke soda-lime tubing of iS m.m. external diameter andv2"5 

 m.m. thickness. Pieces of this tubing broke at a mean 

 hydraulic pressure of 70 atmospheres. Green glass tubing of 

 2"S mm. thickness withstood the explosion ; it broke at a 

 pressure of 140 atmospheres. More exact results were obtained 

 when the gases were diluted with an equal volume of nitrogen : 

 —C.N. -r O5 -f 2N3 = 2CO + 3N5. 



Pieces of the tube which were broken by the explosion were 

 broken hydraulically at 63 atmospheres ; pieces of the tube 

 which withstood the explosion were broken hydraulically at S4 

 atmospheres. 



Prtisura in the Explosion IVave. 



Gaseous mixture. 



Calculated pressures. 

 kieni.tnn. Dixon. 



Observed 

 pressures. 



C,Xj -^ o. 



140 At. 117 M. 70- 140 



-I- 



C.N-, -I- Oj H- 2N. 73S At. I 57 At. 63-84 



When oxygen is added to these mixtures the rate of explosion 

 is diminished and the pressure falls. For instance, according 

 to Kiemann's equation, the pressures produced in the explosion 

 of acetylene with increasing quantities of oxygen are as 

 follow : — 



In the same way the pressures produced in the explosion of 

 ethylene with different quantities of oxygen may be calcu- 

 lated :— 



The lowest of these pressures is probably sufficient to break 

 the cylinders used by Prof. Lothar Meyer. As Prof. Thorpe 

 says in Nature, the danger of acetylene lies in the rapidity 

 with which the explosion-wave is initiated, even when the air 

 alone is used as " tamping." Safety lies not in thickening the 

 glass, but in shortening the tubes. H. B. Dl.\ON. 



Owens College, December i. 



The Kinetic Theory of Gases. 



I HAVE to thank Mr. Culverwell for bis reply to my letter 

 on the discussion at Oxford. To quote his own words (in 

 answering Mr. liurbury, p. 105J, Mr. Culvcrwell's letter was 

 " exactly the kind of letter that I hoped to elicit," as I had 

 not been able to recall the exact purport of Prof. Fitzgerald's 

 "onslaught." Although Prof, liultzmann made no attempt to 

 answer Prof. Fitzgerald's objections in the short space of time 



NO. 131 I, VOL. 51] 



available after the other speakers had concluded, he several 

 times mentioned the question to me after the debate as one 

 which had not been hitherto satisfactorily cleared up. In pre- 

 paring my Report, the question of the spectra of gases came 

 prominently before me, but I purposely refrained from express- 

 ing my own opinions on a subject about which so little had been 

 written in a report which was intended to be chiefly a record ol 

 work actually done. My frequent allusions to the question of 

 the uniqueness of the Bollzmann-Maxwell Law were intended, 

 however, to pave the way, if possible, for an explanation of the 

 discrepancies alluded to by Prof. Fitzgerald, and I should like 

 now to attempt to answer some of his objections. 



According to Mr. Culverwell, Prof. Fitzgerald asked why the 

 ether, the solar system, and the whole universe were not sub- 

 ject to the Boltzmann-Ma.xwell Law ? Let us take the solar 

 system first. 



The law is obviously inapplicable to a single system (as I 

 pointed out in my Report, and hope to prove still more con- 

 clusively shortly). In order to apply it, Prof. Fitzgerald 

 would have to take an infinitely iar^e number oj sular 

 systems, each consisting of similarly constituted planets differ- 

 ing, however, in their motions. What the law states is 

 that, if the coordinates and momenta of the different systems 

 were at any instant distributed according to the Boltzmann- 

 Maxwell distribution {i.e. with frequencies proportional to e - ''•), 

 they would be so distributed at any subsequent instant In the 

 absence of mutual action between the various solar systems, this 

 would not be the only permanent distribution, nor would there 

 be any tendency to assutne such a distribution. If, however, 

 the different solar systems were to collide with or encounter one 

 another at random in such a way that transference of energy 

 was liable to take place between any of the coordinates ol any 

 one system and any of the coordinates of any other system, the 

 Boltzmann-Maxwell distribution tiw/A.' probably be unique,and 

 there would be a tendency to assume such a distribution as 

 the ultimate result of .i great number of encounters taking place. 

 Will not Prof. Fitzgerald agree to this? 



With regard to the ether, I notice that Mr. Culverwell 

 emphasises Prof. Fitzgerald's contention that the investigations 

 ought to lake " ethereal " as well as " molecular " coordinates 

 and momenta into account. But here I agree with Prof. Boltz- 

 mann that the onus probandi lies with physicists. If they will 

 give us a clear and definite statement as to what arc the co- 

 ordinates and momenta of the ether., and how transference oj 

 energy lakes place hel-vc<n these and the molecules, and if they 

 will show that the Boltzmann-Maxwell Law is violated under 

 conditions under which we have proved it to be unique, a " true 

 bill will have been found." 



.\t present all we assert is that if the " ethereal coordinates 

 and momenta " satisfy a determinantal relation similar to that 

 proved on p. 22 of Dr. Watson's new edition, the Boltzmann- 

 Maxwell distribution, // // ever once existed, will be permanent 

 in the absence of disturbing influents. But the test case in 

 which molecules are regarded as smooth solids symmetrical about 

 an axis (see my Report, § 45, case iii.) affords an instance in 

 which partition of energy does not t.ike place between all the 

 coordinates of a system, the angular velocity of each molecule 

 about its axis of symmetry being constant and unaffected by 

 collisions, and therefore independent of the Bollzm.inn- 

 Maxwell Law. .\nd why should not a similar explanation 

 be applicable to the ether ? -At any rate, this hypothesis is sup- 

 ported by the views advanced by I'rof. Oliver Lodge at the Not- 

 tingham meeting of the British Association (" Nottingham 

 Report," p. 688). G. M. Bryan. 



Cambridge, November 30. 



It appears to me that the difficulty raised by recent critics 

 against Maxwell's law of partition of energy in the theory of 

 ga^cs, and Bollzmann's minimum theorem relating thereto, by 

 consideration of the effect of a complete reversal of the motions, 

 is capable of direct explanation ; and that whatever weak points 

 the theory may have, they are not in that direction. Indeed, if 

 that were not so, the criticism would apply equally against the 

 Second Law of Thermodynamics. 



The theorem in question is that there exists a positive function 

 belonging to a group of molecules, which as they settle them- 

 selves into a steady slate maintains— on the average derived 

 from a great number of configurations — a steady downward 

 trend ; ihat the .Maxwcll-Boltzmann steady slate is that one for 



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