Ml*. Ivory on Mixed Gases. 83 



theory of Dalton,now so far universally adopted, which regards 

 the separate condition of different gases, not acting chemi- 

 cally upon one another, when they are confined in the same 

 envelop : every gas is in equilibrium by the elastic force of 

 its own particles, as would be the case if it occupied by itself 

 the whole space of the envelop. It also agrees with the fact 

 that no change of temperature is produced by the expansion 

 of the gases in mixing; for the agitations caused by the second 

 gas in forcing its way through the first one, which is quiescent 

 and in equilibrium, *are attended by alternate condensations 

 and dilatations that produce neither gain nor loss of heat. 



In what regards the elasticity of the mixture, the result ob- 

 tained above likewise agrees with the usual theory, but not 

 with the opinion of Dalton. According to the usual theory 

 the elastic force of the mixture is equal to the sum of the 

 elasticities of the constituent gases, supposing that these elas- 

 ticities are reduced to the volume of the mixture ; which is 

 equivalent to what P stands for. 



When several elastic fluids are mixed in the same envelop, 

 Dalton is of opinion that the elastic force which every one im- 

 presses on the envelop is independent of the action of all the 

 rest, and the same it would be if these were not present. But 

 in forming this opinion the illustrious philosopher has not re- 

 marked that, as every space of the envelop is in contact with 

 all the fluids, a pressure on any such space, produced by what- 

 ever cause, will necessarily be transmitted with equal energy 

 to all the particles of the several fluids. Thus, when all the 

 conditions of the question are taken into account, it appears 

 that every particle within the envelop has the same elastic 

 energy impressed upon it as in the case of a simple gas : if it 

 were not so there could not possibly be an equilibrium of the 

 whole mass. In corroboration of this it may be observed that 

 only one sound is propagated through a mixture of gases such 

 as we have been considering ; whereas if every gas were sepa- 

 rately in equilibrium, without any mutual action of the several 

 fluids, there would be as many different sounds moving with 

 different velocities as there are gases in the mixture. 



XIV. Notice of the Discovery of some remains of the Ichthyo- 

 saurus in Ireland. jRy James Bryce, Jm?., M.A.^ F.G.S. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN May 1831 I published in your Magazine a short notice 

 of the discovery of remains of the Plesiosaurus in this 

 neighbourhood*. Since that time detached saurian vertebrae 

 • They were discovered by Mr. John 11. Smythe of Carnmoney. 

 G2 



