MATTER AND FORCE 75 



our decompositions took place. And just as the molecu- 

 lar attractions of the silver and the lead found expression 

 in those beautiful branching forms seen in our experi- 

 ments, so do the molecular attractions of the liberated 

 carbon and hydrogen find expression in the architecture 

 of grasses, plants, and trees. 



In the fall of a cataract and the rush of the wind we 

 have examples of mechanical power. In the combina- 

 tions of chemistry and in the formation of crystals and 

 vegetables we have examples of molecular power. You 

 have learned how the atoms of oxygen and hydrogen 

 rush together to form water. I have not thought it nec- 

 essary to dwell upon the mighty mechanical energy of 

 their act of combination; but it may be said, in passing, 

 that the clashing together of 1 Ib. of hydrogen and 8 Ibs. 

 of oxygen to form 9 Ibs. of aqueous vapor is greater 

 than the shock of a weight of 1,000 tons falling from a 

 height of 20 feet against the earth. Now, in order that 

 the atoms of oxygen and hydrogen should rise by their 

 mutual attractions to the velocity corresponding to this 

 enormous mechanical effect, a certain distance must exist 

 between the particles. It is in rushing over this that the 

 velocity is attained. 



This idea of distance between the attracting atoms is 

 of the highest importance in our conception of the sys- 

 tem of the world. For the matter of the world may be 

 classified under two distinct heads: atoms and molecules 

 which have already combined and thus satisfied their 

 mutual attractions, and atoms and molecules which have 

 not yet combined, and whose mutual attractions are, 

 therefore, unsatisfied. Now, as regards motive power, 



