DIVISIBILITY OF MATTER ATOMIC THEORY. 73 



atoms or molecules is put into work. The evidence that 

 under equal pressure and temperature every different 

 gas contains in the same volume the same number of 

 molecules, is one striking result of research thus 

 directed. The experiments of Graham on the inter- 

 diffusion of gases and liquids have thrown much curious 

 light on the subject, and coupled with other consider- 

 ations go far to justify the hypothesis, propounded by 

 himself, that the atoms or molecules of all gases are 

 spherical in form, incessantly in movement in every 

 direction, but with varying velocity in different gases. 

 Granting this to be hypothetical only, yet are the con- 

 ditions resulting from experiment such as to make it 

 difficult to supply other interpretation. We feel in a 

 certain proximity to the truth, though the conclusive 

 and final steps still remain to be made. Similar antici- 

 pations are frequent in other parts of science, cheering 

 as well as directing the labours of research. 



To gases and vapours, as already mentioned, we 

 may especially look for elucidation of the forms and 

 properties of molecular compounds, founded on their 

 varying relation to those radiant forces (as we must 

 conventionally call them) which govern the intimate 

 motions of matter in all its shapes. The strong pre- 

 sumption already existing that compound atoms, or 

 molecules, must differ from simple atoms in size, or 

 figure, or both, has been strikingly confirmed by the 

 experiments of Tyndall, showing the large absorption, 

 or stoppage, of radiant heat occurring in its passage 

 through compound gases, compared with what happens 

 in those of simple elementary kind. These results, like 



