114 NOVUM OKGAMJM. 



in which respect I have observed, that if a glass be placed 

 at the distance of ten inches, for instance, from the combus 

 tible object, it does not kindle or burn it so readily, as if 

 the glass be placed at the distance of five inches (for in 

 stance), and be then gradually and slowly withdrawn to the 

 distance of ten inches. The cone and focus of the rays, 

 however, are the same, but the mere motion increases the 

 effect of the heat. 



29. Conflagrations, which take place with a high wind, 

 are thought to make greater way against than with the 

 wind, because when the wind slackens the flame recoils 

 more rapidly than it advances when the wind is favourable. 



30. Flame does not burst out or arise unless it have 

 some hollow space to move and exert itself in, except in the 

 exploding flame of gunpowder, and the like, where the com 

 pression and confinement of the flame increase its fury. 



31. The anvil becomes so hot by the hammer, that if it 

 were a thin plate it might probably grow red like ignited 

 iron by repeated strokes. Let the experiment be tried. 



32. But in ignited bodies that are porous, so as to leave 

 room for the fire to move itself, if its motion be prevented 

 by strong compression, the fire is immediately extinguished ; 

 thus it is with tinder, or the burning snuff of a candle or 

 lamp, or even hot charcoal or cinders, for when they are 

 squeezed by snuffers, or the foot, and the like, the effect of 

 the fire instantly ceases. 



33. The approach towards a hot body increases heat in 

 proportion to the approximation ; a similar effect to that of 

 light, for the nearer any object is placed towards the light^ 

 the more visible it becomes. 



34. The^ union of different heats increases heat, unless 

 the substances be mixed. For a large and small fire in the 

 same spot tend mutually to increase each other s heat, but 

 lukewarm water poured into boiling water cools it. 



35. The continued neighbourhood of a warm body in 

 creases heat. For the heat, which perpetually passes and 

 emanates from it, being mixed with that which preceded it, 

 multiplies the whole. A fire, for instance, does not warm 

 a room in half an hour, as much as the same fire would in 

 an hour. This does not apply to light, for a lamp or candle 

 placed in any spot gives no more light by remaining there, 

 than it did at first. 



* The fires supply fresh heal, the water has only a certain quantity of heat, 

 which being diffused over a fresh supply of cooler water must be on the whole 

 lowered. 





