1863.] 621 



the result. The gaseous molecule must itself be viewed as composed 

 of a group or system of the preceding inferior atoms, following as a 

 unit laws similar to those which regulate its constituent atoms. We 

 have indeed carried one step backward and applied to the lower order 

 of atoms ideas suggested by the gaseous molecule, as views derived 

 from the solar system are extended to the subordinate system of a 

 planet and its satellites. The advance of science may further require 

 an indefinite repetition of such steps of molecular division. The 

 gaseous molecule is then a reproduction of the inferior atom on a 

 higher scale. The molecule or system is reached which is affected 

 by heat, the diffusive molecule, of which the movement is the subject 

 of observation and measurement. The diffusive molecules are also 

 to be supposed uniform in weight, but to vary in velocity of move- 

 ment, in correspondence with their constituent atoms. Accordingly 

 the molecular volumes of different elementary substances have the 

 same relation to each other as the subordinate atomic volumes of the 

 same substances. 



But further, these more and less mobile or light and heavy forms 

 of matter have a singular relation connected with equality of volume. 

 Equal volumes of two of them can coalesce together, unite their 

 movement, and form a new atomic group, retaining the whole, the 

 half, or some simple proportion of the original movement and conse- 

 quent volume. This is chemical combination. It is directly an affair 

 of volume, and only indirectly connected with weight. Combining 

 weights are different, because the densities, atomic and molecular, are 

 different. The volume of combination is uniform, but the fluids 

 measured vary in density. This fixed combining measure the 

 metron of simple substances weighs 1 for hydrogen, 1 6 for oxygen, 

 and so on with the other " elements. " 



To the preceding statements respecting atomic and molecular mo- 

 bility, it remains to be added that the hypothesis admits of another 

 expression. As in the theory of light we have the alternative hypo- 

 theses of emission and undulation, so in molecular mobility the motion 

 may be assumed to reside either in separate atoms and molecules, or 

 in a fluid medium caused to undulate. A special rate of vibration or 

 pulsation originally imparted to a portion of the fluid medium enlivens 

 that portion of matter with an individual existence,, and constitutes it 

 a distinct substance or element. 



