334 LAUGEL'S PROBLEMS OF NATURE AND LIFE. 



illustration of the phenomena of the effusion and diffu- 

 sion of gases through each other, and through interven- 

 ing septa of different substances, has done more than 

 any other experimentalist in materialising atoms and 

 molecules to our comprehension ; by showing their dis- 

 tinctive and relative modes of action, their separation 

 even from what we call chemical combination by other 

 than chemical reactions, and their different capacity 

 and rate of penetration through the porous media used 

 to effect this separation. When we are told that the 

 pores of graphite (one substance employed as a septum) 

 are so minute that a gas cannot pass through in mass, 

 but in molecules only, we obtain a certain relative 

 comprehension of atomic elements, and an index to 

 collateral enquiry in this very interesting branch of 

 physics. Such enquiry cannot fail to be pursued fur- 

 ther. In his paper on the molecular mobility of gases 

 Mr. Graham enlarges upon and justifies the belief that 

 continual intestine movement of atoms or molecules is 

 an essential condition of matter in a gaseous state, 

 these movements being different in different gases. 

 This inference, indeed, is almost inevitable from the 

 experiments he has recorded, and serves to interpret 

 other known phenomena, which scarcely admit of being 

 otherwise explained. 



Let us here notice in passing that Lucretius, that 

 wonderful poet and the predictor of much that has 

 been proved and amplified by later research, fore- 

 shadows in some sort the recent discoveries of Graham 

 and others on the diffusibility and penetrability of 

 different kinds of matter (lib. ii. 288, et seq.). His 



