THE ACTIONS OF FORCES ON ORGANIC MATTER. 29 



classes of the ethereal undulations penetrating their leaves, 

 plants are enabled to separate from the associated oxygen, 

 those two elements of which their tissues are chiefly built 

 up. 



This transformation of ethereal undulations into certain 

 molecular re-arrangernents of an unstable kind, on the over- 

 throw of which the stored-up forces are liberated in new 

 forms, is a process that underlies all organic phenomena. It 

 will therefore be well, if we pause a moment to consider whe- 

 ther any proximate interpretation of it is possible. Certain 

 recent researches in molecular physics, give us some clue to 

 its nature. 



The elements of the problem are these : The atoms of 

 several ponderable matters exist in combination : those that 

 are combined having strong affinities, but having also affin- 

 ities less strong for some of the surrounding atoms that are 

 otherwise combined. The atoms thus united, and thus mixed 

 among others with which they are capable of uniting, are 

 exposed to the undulations of a medium that is relatively so 

 rare as to seem imponderable. These undulations are of 

 numerous kinds : they differ greatly in their lengths, or in 

 the frequency with which they recur at any given point. 

 And under the influence of undulations of a certain frequency, 

 some of these atoms are transferred from atoms for which they 

 have a stronger affinity, to atoms for which they have a weaker 

 affinity. That is to say, particular orders of waves of a rela- 

 tively imponderable matter, remove particular atoms of pon- 

 derable matter from their attachments, and carry them within 

 reach of other attachments. Now the discoveries of 



Bunsen and Kirchoff respecting the absorption of particular 

 luminiferous undulations by the vapours of particular sub- 

 stances, joined with Prof. TyndalPs discoveries respecting 

 the absorption of heat by gases, show very clearly that the 

 atoms of each substance have a rate of vibration in harmony 

 with ethereal waves of a certain length, or rapidity of recur- 

 rence. Every special kind of atom can be made to oscillate 



