MATTER AND FORCE 69 



gen on the other. The gases may be collected either 

 separately or mixed. I place upon my hand a soap 

 bubble filled with the mixture of both gases. Apply- 

 ing a taper to the bubble, a loud explosion is heard. 

 The atoms have rushed together with detonation, and 

 without injury to my hand, and the water from which 

 they were extracted is the result of their reunion. 



One consequence of the rushing together of the atoms 

 is the development of heat. What is this heat? Here 

 are two ivory balls suspended from the same point of 

 support by two short strings. I draw them thus apart 

 and then liberate them. They clash together, but, by 

 virtue of their elasticity, they quickly recoil, and a sharp 

 vibratory rattle succeeds their collision. This experiment 

 will enable you to figure to your mind a pair of clashing 

 atoms. We have, in the first place, a motion of the one 

 atom toward the other a motion of translation, as it is 

 usually called then a recoil, and afterward a motion of 

 vibration. To this vibratory motion we give the name 

 of heat. Thus, three things are to be kept before the 

 mind first, the atoms themselves; secondly, the force' 

 with which they attract each other; and, thirdly, the 

 motion consequent upon the exertion of that force. This 

 motion must be figured first as a motion of translation, 

 and then as a motion of vibration, to which latter we 

 give the name of heat. For some time after the act of 

 combination this motion is so violent as to prevent the 

 molecules from coming together, the water being main- 

 tained in a state of vapor. But as the vapor cools, or, 

 in other words, loses its motion, the molecules coalesce 

 to form a liquid. 



