168 BIOGRAPHICAL MEMOIR OF JOSEPH HENRY. 



The forces of gravity, cohesion, electricity, and chemical attraction 

 tend to produce a state of permanent equilibrium on our planet ; lience 

 these principles in themselves are not primary, but secondary, agents in 

 producing mechanical effects. 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 pri- 

 mary 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 phenomena of combustion, the immediate source of the 

 power evolved iu 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 re- 

 solved into the force which caused the separation of these elements from 

 their x)revious 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 i)assage of organized matter in the stomach from an un- 

 stable to a stable equdibrium, 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 1 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. Suppose a 

 vegetable organism impregnated with a germ — a potato, for instance — 

 is planted below the surface of the ground in a damp soil, under a tem- 

 perature sufficient for vegetation. If we examine it from time to time, we 

 find it sending down rootlets into the earth and stems and leaves upward 

 into the air. After the leaves have been fully expanded we shall find the 

 tuber entirely exhausted, nothing but a skin remaining. The same effect 

 will take place if the potato be placed in a warm cellar. It will con- 

 tinue to grow until all the starch and gluten are exhausted, when it will 

 cease to increase. If, however, we now place it iu the light, it will com- 

 mence to grow again, and increase in size and weight. K we weigh the 

 potato previous to the experiment and the plant after it has ceased to 

 grow in the dark, we shall find that the weight of the latter is a little 

 more than half that of the original tuber. The question then is, what 

 has become of the material which filled the sac of the potato ? The an- 

 swer is, one part has run down into carbonic acid and water, and iu this 

 running down has evolved the power to build up the other part into the 

 new i)lant. After the leaves have been formed and the plant exposed to 

 the light of the sun, the developed power of its rays decomposes the car- 

 bonic acid of the atmosphere, and thus furnishes the pabulum and the 

 power necessary to the further development of the organization. The 

 same is the case ^vith wheat and all other grains that are germinated in 

 tlie earth. Besides the germ of the futiu'e plant, there is stored away 

 around the germ the starch and gluten to furnish the power necessary 

 to its development and also the food to build it up until it reaches 

 tlie surface of the earth and can draw the source of its future growth 

 from the power of the sunbeam. In the case of fungi and other plants 

 that grow in the dark, they derive the power and the pabulum from sur- 

 rounding vegetable matter in process of decay or in that of evolving 

 power. A similar arrangement is found in regard to animal organiza- 

 tion. It is well known that the egg continually diminishes in weight dur- 

 ing the process of incubation, and the chick when fully formed weighs 

 scarcely more than one-half the original weight of the egg. What is the 



