Mr. Dalton on the constitution of the atmosphere, 1 75 



nical effects, we may safely adopt the above hypothesis within 

 the fore-mentioned limits of condensation and rarefaction. 



The existence of elastic fluids totally different from atmo- 

 spheric air in their chemical nature, but agreeing with it in 

 mechanical properties, was unknown in Newton's time. Such 

 fluids are now known to exist ; they may be mixed together, 

 and, in case no obvious chemical action ensues, they are 

 found to occupy the same space after as before mixture, and 

 in due time to be uniformly diffused through the space the 

 mixture occupies, whatever may be the difference of their 

 volumes and specific gravities : and such mixtures have all the 

 mechanical properties of simple elastic fluids, as the atmosphere 

 itself evinces, which is a mixture of at least four such elastic 

 fluids. 



Whether the uniform diffusion of elastic fluids through 

 each other is occasioned by the repulsion of the elementary 

 particles of the same kind, which appears to force them 

 through most bodies, as well solid and liquid as aerial, except 

 glass and the metals ; or whether it is caused by attraction 

 or chemical affinity, may be doubted. Difficulties attend 

 both views. I have long been inclined to adopt the former 

 notion as most consistent with the phenomena. According 

 to this view the particles of any elastic fluid (A) are endued 

 with repulsion to each other by the Newtonian law above 

 stated ; also those of any other (B) repel each other in like 

 manner ; but the particles of (A) do not repel those of (B), 

 or rather are inelastic in regard to them. Such mixture must 

 evidently possess the mechanical law of condensation which 

 the atmosphere possesses, and which Newton's imaginary 

 homogeneous fluid possesses. 



