MATTER AND FORCE. 389 



electric current from wire to wire. Bubbles of gas rise 

 immediately from each of them, and these are the two 

 gases of which the water is composed. The oxygen is 

 always liberated on the one wire, the hydrogen 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. Applying 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 liber- 

 ate them. They clash together, but, by virtue of their elas- 

 ticity, 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 fig- 

 ured 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 maintained in a state of vapor. But as the 

 vapor cools, or in other words loses its motion, the mole- 

 cules coalesce to form a liquid. 



And now we approach a new and wonderful display of 

 force. As long as the substance remains in a liquid or 

 vaporous condition, the play of this force is altogether 

 masked and hidden. But as the heat is gradually with- 

 drawn, the molecules prepare for new arrangements and 

 combinations. Solid crystals of water are at length formed, 

 to which we give the familiar name of ice. Looking at 

 these beautiful edifices and their internal structure, the 



