3 86 



BACON 



XXX. 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 gun- 

 powder, and the like, where the compression and confinement of the 

 flame increase its fury. 



XXXI. 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. 



XXXII. 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 com- 

 pression, the fire is immediately extinguished; thus it is with tinder, 

 or the burning snuff of a candle or lamp, or even hot charcoal or cin- 

 ders; for when they are squeezed by snuffers, or the foot, and the like, 

 the effect of the fire instantly ceases. 



XXXIII. The approach towards a hot body increases heat in pro- 

 portion to the approximation; a similar effect to that of light, for the 

 nearer any object is placed towards the light, the more visible it be- 

 comes. 



XXXIV. The union of different heats increases heat, unless the sub- 

 stances 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. 



XXXV. The continued neighborhood of a warm body increases 

 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 a spot gives no more light by remaining there, than 

 it did at first. 



XX XVI. The irritation of surrounding cold increases heat, as may 

 be seen in fires during a sharp frost. We think that this is owing not 

 merely to the confinement and compression of the heat (which forms a 

 sort of union), but also by the exasperation of it, as when the air or a 

 stick is violently compressed or bent, it recoils, not only to the 

 point it first occupied, but still farther back. Let an accurate ex- 

 periment, therefore, be made with a stick, or something of the kind, 

 put into the flame, in order to see whether it be not sooner burnt at the 

 sides than in the middle of it. 



XXXVII. There are many degrees in the susceptibility of heat. 

 And, first, it must be observed how much a low gentle heat changes 

 and partially warms even the bodies least susceptible of it. For even 

 the heat of the hand imparts a little warmth to a ball of lead or other 

 metal held a short time in it ; so easily is heat transmitted and excited, 

 without any apparent change in the body. 



XXXVIII. Of all bodies that we are acquainted with, air admits 

 and loses heat the most readily, which is admirably seen in weather- 

 glasses, whose construction is as follows. Take a glass with a hollow 

 belly, and a thin and long neck; turn it upside down, and place it with 

 its mouth downwards into another glass vessel containing water; the 

 end of the tube touching the bottom of the vessel, and the tube itself 

 leaning a little on the edge, so as to be fixed upright. In order to do 

 this more readily, let a little wax be applied to the edge, not however 

 so as to block up the orifice, lest by preventing the air from escaping, 

 the motion, which we shall presently speak of, and which is very gentle 

 and delicate, should be impeded. 



Before the first glass be inserted in the other, its upper part (the 

 belly) should be warmed at the fire. Then upon placing it as we have 

 described, the air (which was dilated by the heat), after a sufficient 

 time has been allowed for it to lose the additional temperature, will re- 



