92 Prof. Liveing, On the probable presence in the Sun, etc. 



have licked up all the gases out of planetary space. For if we 

 could suppose that, and the earth with its atmosphere moving 

 through empty space, the incoherent atmosphere must, I suppose, 

 distribute itself in a long trail throughout the earth's orbit, and 

 this trail would rapidly diffuse into the void space, and the process 

 of diffusion would go on until the amount lost by the earth in 

 its course was counterbalanced by the amount licked up, in fact 

 until gas at a certain average density was distributed throughout 

 the whole of the space in which the earth circulates. That 

 average density will be the same whether we suppose the earth 

 to start with its atmosphere in void space, or to start with a less 

 dense atmosphere in space filled with gas of greater density than 

 that average. Also the distribution of the several gases which 

 have molecules of different masses will ultimately be the same 

 in these two cases. The proportion of gases of smaller molecular 

 mass will increase outwards from the earth's surface as well as 

 from that of the sun, and the interchange between the sun and 

 earth will go on most quickly in the case of the gases of least 

 molecular mass, or in fact those which are most volatile. 



