162 MEMORIAL OF JOSEPH HENRY. 



The following is a list which will be found to include all the 

 prime movers used at the present day, either directly or indirectly, 

 in producing molecular changes in matter : 



( Water power. ^ Immediately referable 



CLASS I. < Tide power. > to celestial disturb- 



( Wind power. J ance. 



( Steam and other powers "j Immediately referable 

 CLASS II. < developed by combustion. > to what is called 

 (Animal power. J vital action. 



The forces of gravity, cohesion, electricity, and chemical attrac- 

 tion tend to produce a state of permanent equilibrium on our 

 planet ; hence these principles in themselves are not primary, but 

 secondary agents in producing mechanical eifects. As an example, 

 we may take the case of water-power, which is approximately due 

 to the return of the water to a state of stable equilibrium on the 

 surface of the ocean ; but the primary cause of the motion is the 

 force which produced the elevation of the liquid in the form of 

 vapor namely, the radiant heat of the sun. Also in the pheno- 

 mena of combustion, the immediate source of the power evolved in 

 the form of heat is the passage from an unstable state into one of 

 stable combination of the carbon and hydrogen of the fuel with 

 oxygen of the atmosphere. But this power may ultimately be 

 resolved into the force which caused the separation of these elements 

 from their previous combination in the state of carbonic acid 

 namely, the radiant light of the sun. But the mechanical power 

 exerted by animals is due to the passage of organized matter in the 

 stomach from an unstable to a stable equilibrium, or as it were 

 from the combustion of the food. It therefore follows that animal 

 power is referable to the same source as that from the combustion 

 of fuel namely, developed power of the sun's beams. But 

 according to this view, what is vitality? It is that mysterious 

 principle not mechanical power which determines the form and 

 arranges the atoms of organized matter, employing for this purpose 

 the power which is derived from the food. 



These propositions were illustrated by different examples. Sup- 

 pose a vegetable organism impregnated with a germ (a potato, for 



