BIOGEAPHICAL MEMOIR OF JOSEPH HENEY. 1G7 



plates, and from tlie results the conclusion was arrived at that the at- 

 tractive force of the molecules of water, for those of water, is approxi- 

 mately equal to that of the molecules of ice for those of ice, and that the 

 difiereuce in this case, of the solidity and liquidity, is due to the want of 

 mobility in the latter, which prevented the slipping of the molecules on 

 each other. It is this extreme mobility of the molecules of water that 

 prevents the formation of permanent bubbles of it, and not a want of 

 attraction. 



The roundness of drops otf water is not due to the attraction of the 

 whole mass, but merely to the action of the surface, which in all cases 

 of curvature is endowed with an intense contractile power. 



This class of investigation also included the study of soap bubbles, 

 and the establishment of the fact of the contractile power of these films. 

 The curvature of the surface of a bubble tends to urge each particle 

 toward the center, witb a force inversely as the diameter. Two bubbles 

 being connected, the smaller will collapse by expelling its contents into 

 the larger. By employing frames of wire, soap bubbles were also made 

 to assume various forms, by which capillarity and other phenomena 

 were illustrated. This subject was afterward taken up by Plateau, of 

 Ghent. Another part of the same investigation was the study of the 

 spreading of oil on Avater, the phenomenon being referred to the fact that 

 the attraction of water for water is greater than that of oil for oil, while 

 the attraction of the molecules of oil for each other is less than the 

 attraction of the same molecules for water ; hence the oil spreads over 

 the water. This is shown from the tact that when a rupture is made in 

 a liquid compound, consisting of a stratum of oil resting on water, the 

 rupture takes place in the oil, and not between the oil and water. The 

 ■sery small distance at which the attraction takes place, is exhibited by 

 placing a single drop (»f oil on a surface of water of a considerable ex- 

 tent, when it will diffuse itself over the whole surface. If, however, a 

 second drop be placed upon the same surface, it Avill retain its globular 

 form. 



XVI. Another contribution to science had reference to the origin of 

 mechanical power and the nature of vital force. Mechanical power is 

 defined to be that which is capable of overcoming resistance ; or, in the 

 language of the engineer, that which is employed to do work. 



If we examine attentively the condition of the crust of the eartb, we 

 find it, as a general rule, in a state of permanent equilibrium. All the 

 substances which constitute the material of the crust, such as acids and 

 bases, with the exception of the indefinitely thin pellicle of vegetable 

 and animal matter which exists at its suiface, have all gone into a state 

 of permanent combination, the whole being in the condition of a burnt 

 slag of a furnace, entirely inert, and capable in itself of no change. All 

 thechanges which we observe on the surface of the globe may be referred 

 to action from without, from celestial space. 



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 produc- 

 ing molecular changes in matter : 



C Water power. ^ Immediately referable 



Class I. } Tide power. > to celestial disturb- 



( Wind power. ) ance. 



( Steam and other powers devel- ^ Immediately referable to 

 Class II. } oped by combustion. > wliat is called vital 



( Animal power. ) action. 



