MATTER AND FORCE. 81 



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 two gases may be collected separately ; in 

 fact, they have been thus collected in these jars. A lighted 

 taper placed in one jar inflames the gas, which proves it to 

 be hydrogen ; a burning ember of wood placed in the 

 other jar instantly bursts into vivid combustion, which 

 proves the gas in the jar to be oxygen. I place upon my 

 hand a soap-bubble filled with a mixture of both gases in 

 the exact proportions in which they exist in water. Apply- 

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

 gases have rushed together with detonation, but without 

 injury to my hand, and the water from which they were 

 extracted is the result of the reunion. 



I wish you to see with the utmost possible clearness 

 what has here taken place. Fust, then, you are to re- 

 member that to form water the proportions by weight of 

 oxygen and hydrogen are as eight to one. Eight ounces 

 of oxygen, for example, unite with one of hydrogen to 

 form nine ounces of water. But if, instead of comparing 

 weights, we compare volumes, two volumes of hydrogen 

 unite with one of oxygen to form water. Now, these vol- 

 umes, and not the weights, express the proportions in 

 which the atoms of hydrogen unite with those of oxygen. 

 In the act of combination two atoms of hydrogen combine 

 with one of oxygen to form what we call the molecule of 

 Avater. Every such molecule is a group of three atoms, 

 two of which are hydrogen and one oxygen. 



One consequence of the rushing together of the atoms 

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

 are we to figure it before our minds ? I do not despair of 

 being able to give you a tolerably distinct answer to this 

 question. Here are two ivory balls suspended from the 

 same point of support by two short strings. I draw them 



