August 3, 1883.] 



SCIENCE. 



125 



But it is to be noticed that the impulses 

 due to the vibrations of the chemical atoms 

 within a molecule are vastly more frequent 

 than the molecular impulses ; and it appears 

 probable that the vihi'utions of the chemical 

 atoms set up during an encounter will rapidly 

 decay, even in case they do not themselves 

 directl}' originate radiations. The vibratory 

 energy of this kind may then be changed 

 almost instantly into that of vibration of the 

 ultimate atoms. 



According to the hypothesis which we are 

 now considering, the temperature of the body 

 and the intensity of the radiation depen<l solely 

 on the vibratory energy of the ultimate atoms ; 

 but, since these ultimate atoms are assumed to 

 be in all respects equal, the}- vibrate under the 

 action of the same forces, and have the same 

 degrees of freedom and constraint within the 

 chemical atoms of one element as they do 

 within those of a different element. Hence 

 it appears, that if the ultimate atoms of two 

 different gases have the same vibratory energy 

 (i.e., cause vibrations of the same intensity), 

 so that the flow of radiant energy is the same 

 from all the ultimate atoms of each gas, then 

 there will be no disturbance of this equilib- 

 rium when these gases are mixed ; in which 

 case the distribution of energy is effected by 

 molecular encounters, which distribute equal 

 mean amounts of energy to each molecule, in- 

 stead of l)y radiations, which distribute equal 

 mean amounts of energy to each ultimate atom. 

 In attempting to account for the high specific 

 heat of liquids, I have elsewhere given reasons 

 for supposing that it is due to a certain per 

 cent of dissociation, which increases with the 

 temperature. It api)ears probable, that, al- 

 though some small amount of dissociation may 

 exist in gases also, there is not so large a per 

 cent as in the liquid state, nor does the per 

 cent necessarily increase with the temperature ; 

 for by reason of the free progressive motion in 

 a gas, which does not e.vist in a liquid, any 

 dissociated atoms have a much better opportu- 

 nity to recombine ; and, as the velocities (espe- 

 cially those of free atoms) increase with the 

 temperature, these opportunities increase, as 

 well as the number of dissociations occurring 

 in a unit of time ; so that, at a high tempera- 

 ture, an atom of gas may not stay dissociated 

 so long as at a lower temperature, while in a 

 liquid this interval will not be sensibly affected 

 by the temperature. 



" It is thought that the law of Dulong and 

 Petit receives reasonable explanation on the 

 hypothesis that the ultimate atoms have each 

 the same kinetic energv at the same temper- 



ature, as will be shown in a subsequent paper : 

 but perhaps the strongest direct evidence in 

 favor of the proposed hypothesis is found in the 

 fact that even the simplest elements, such as 

 hydrogen or mercury, have spectra of several 

 lines at least, showing that the source of the 

 light must be sufficiently complex to be able to 

 vibrate in a numtier of different ways, such as 

 may well be possilile for an atom formed of a 

 number of ultimate atoms, but such as is in- 

 conceivable in a molecule consisting of one or 

 two perfectly hard atoms. H. T. Eddy. 



TliE NATIONAL RAILWAY EXPOSI- 

 TION.^ — IV. 



The exhibit of locomotives was remarkably 

 complete, and comprised engines differing 

 widely in size and power, and adapted for every 

 variety of work ; but a certain uniformity of 

 the design of the main features would seem 

 to indicate that locomotive practice has settled 

 down into a certain groove, and that the meth- 

 ods of construction now adopted are so satis- 

 factory that few exhibiters propose to greatly 

 improve upon them by any radical alterations, 

 though one or two of these new departures, 

 such as the Wootten firebox and the Stevens 

 valve-gear, seem likeh- to come into extensive 

 use. 



The main tendency of locomotive design 

 seems to run rather in the direction of larger 

 bearing surfaces and stronger working parts 

 than in any novel methods of construction ; 

 while sound and accurate workmanship, and 

 plenty of good material judiciously distributed, 

 are relied on to make a locomotive durable, 

 hard-working, and trustworthy under trying 

 conditions. 



Mr. E. Shay of Ilaring. Mich., exhibits a 

 model of an engine of peculiar construction for 

 • loo^criiig ' purposes. These small railways are 

 exceedingly light in construction, and the rails 

 and ties are generally laid directly on the sur- 

 f;\ce of the ground, without any great attention 

 being paid to preUminary grading or align- 

 ment ; and therefore a suitable locomotive must 

 unite considerable tractive power with great 

 flexibility of wheel-base, and a small weight, 

 on anv one pair of wheels. Mr. Shay accom- 

 plishes this by using a Forney type of loco- 

 motive, having a pair of drivers under the barrel 

 of the boiler, and a four-wheel truck, carrying 

 the tank and fuel, behind the Qrebox. All the 

 wheels being made of the same diameter, a pair 

 of vertical engines are secured to one side of 

 the firebox, working a longitudinal shaft which 



> Conlinuivl from No. i'l. 



