326 NOVUM ORGANUM. 



27. Motion increases heat, as we see in the case of bellows and the 

 blast ; insomuch that the harder metals are not melted or liquefied by 

 means of a dull or quiet fire, unless it be quickened by a blast. 



28. Let experiment be made by means of burning lenses, which (as 

 we remember) operate thus : if a lens be placed (suppose) a span 

 distance from the combustible object, it does not kindle or inflame it 

 so readily as it would if it were placed at the distance of (say) half a 

 span, and then moved gradually and slowly to the distance of a span. 

 Yet the cone and union of the rays are the same, but the motion itself 

 increases the operation of the heat. 



29. Those conflagrations which take place when a strong wind is 

 blowing are thought to make greater progress against the wind than 

 with it, because flame recoils with a swifter motion when the wind 

 slackens, than that with which it advances while the wind is driving 

 it on. 



30. Flame does not burst forth, nor is it produced, unless it has some 

 hollow space in which to move and play ; except the explosive flame 

 of gunpowder, and the like, where compression and imprisonment of 

 the flame increases its fury. 



31. The anvil becomes very hot under the hammer, so that were 

 the anvil to consist of a rather thin plate, we imagine it would, under 

 strong and continued blows of the hammer, become red hot, like ignited 

 iron ; but of this let experiment be made. 



32. But in the case of ignited bodies which are porous, and which 

 give space for the fire to move, if this motion be restrained by strong 

 compression, the fire is immediately extinguished ; as when tinder, or 

 the burning wick of a candle or lamp, or even burning charcoal, or 

 coal, is compressed by pincers, or by treading with the foot, or the 

 like, the action of the fire immediately ceases. 



33. Approximation to a hot body increases heat in proportion to the 

 degree of approximation ; and this is also the case with light, for the 

 nearer an object is brought to the light, the more visible it becomes. 



34. The union of different heats increases heat, unless the bodies 

 themselves be mingled. For a great fire and a little fire in the same 

 place increase one another s heat, but tepid water poured into boiling 

 water cools it. 



35. The continued presence of a hot body increases heat. For the 

 heat continually passing through and flowing forth from it, mingles 

 with the previously existing heat, so as to multiply it. A fire does not 

 heat a chamber in half an hour so well as it would if it had been 

 burning a whole hour. But this is not the case with light, for a lamp 

 or a candle gives no more light after burning for some time than it did 

 when first lighted. 



36. Irritation caused by surrounding cold increases heat, as we may 

 see in fires during a sharp frost. And this, we think, is due not only 

 to the confinement and contraction of the heat, which is a kind of 

 union, but to exasperation ; thus when air or a stick is violently com 

 pressed or bent, it does not recoil to its former position, but goes 

 further in the opposite direction. And so let trial be carefully made, 



