170 



dition before the combustion ; but afterward it is in the form 

 of gas, which it is very difficult (though we have succeeded) 

 to produce in a solid or liquid state. 



Now I must take you to a very interesting part of our sub- 

 ject to the relation between the combustion of a candle 

 and that living kind of combustion which goes on within us. 

 In every one of us there is a living process of combustion 

 going on very similar to that of a candle, and I must try to 



FIG. 86 



make that plain to you. For it is not merely true in a 

 poetical sense the relation of the life of man to a taper; 

 and if you will follow, I think I can make this clear. In 

 order to make the relation very plain, I have devised a little 

 apparatus which we can soon build up before you. Here is 

 a board, and a groove cut in it, and I can close the groove at 

 the top part by a little cover ; I can then continue the groove 

 as a channel by a glass tube at each end, there being a 

 free passage through the whole. Suppose I take a taper or 

 candle (we can now be liberal in our use of the word 

 "candle," since we understand what it means), and place it 

 in one of the tubes ; it will go on, you see, burning very well. 

 You observe that the air which feeds the flame passes down 

 the tube at one end, then goes along the horizontal tube, 

 and ascends the tube at the other end in which the taper 

 is placed. If I stop the aperture through which the air 

 enters, I stop combustion, as you perceive. I stop the supply 

 of air, and consequently the candle goes out. But now what 

 will you think of this fact? In a former experiment I 

 showed you the air going from one burning candle to a 



