BLOWING THE FLAME OUT. 69 



Now, in the case of an ordinary fire of wood or of coal, 

 the way to increase the supply of oxygen is to blow it with 

 the bellows ; that is, to send in, by means of the bellows, a 

 rapid current of air containing the necessary oxygen. But 

 it is a curious circumstance that, while the blowing of a 

 solid fire makes it burn all the brighter, blowing the flame 

 of a candle puts it out. What is the reason of this ? 



Fully to understand the reason, it must be observed that 

 blowing a fire has three different effects upon it first, to 

 supply oxygen to it, and so make it burn faster ; secondly, 

 to cool it ; and, thirdly, by its mechanical impulse, to blow 

 the burning fuel away. In the case of the blacksmith's 

 forge, only the first of these effects is produced to any con- 

 siderable extent. The current of air supplies oxygen to 

 increase the combustion, which greatly increases the heat. 

 It brings coolness too, and so prevents the heat from be- 

 coming as great as it would be if the bellows could blow 

 hot air instead of cold ; but the influence of the greater 

 supply of oxygen in promoting the combustion is vastly 

 greater in increasing the heat than the cooling effect, even 

 in the coldest winter day, is in diminishing it. And as to 

 the third effect, the coals being solid and comparatively 

 heavy, the current of air is not strong enough to blow 

 them away. 



If, however, we imagine that the blast was so powerful 

 as to blow the coals from the forge all over the black- 

 smith's shop, the fire would be put out by it at once that 

 is, as soon as the individual coals had time to go out in 

 their new places, scattered over the bench and floor. If 

 the coals were very small, this would be very soon ; and 

 if we imagine each one of them to be no larger than a par- 

 ticle of dust, the extinguishment would be almost instan- 

 taneous. 



This is precisely what happens when we blow out a can- 



