MATTER AND FORCE. 63 



and which we figure as flowing through the wire when 

 the voltaic circuit is complete. 



By the same agent we tear asunder the locked atoms 

 of a chemical compound. Into this small cell, contain- 

 ing water, dip two thin wires. A magnified image of 

 the cell is thrown upon the screen before you, and you 

 see plainly the images of the wires. From a small bat- 

 tery I send an 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 com- 

 posed. 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 re-union. 



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 to- 

 wards the other a motion of translation, as it is usu- 

 ally called then a recoil, and afterwards' 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 



