124 NOVUM ORGANUM. 



swell or dilate in bulk, such as red-hot iron, in which the 

 heat is most violent. 



It is also shown by the fires burning most briskly in the 

 coldest weather. 



It is also shown by this ; that when the air is dilated in 

 the thermometer uniformly and equably, without any im 

 pediment or repulsion, the heat is not perceptible. In con 

 fined draughts also, although they break out very violently, 

 no remarkable heat is perceived, because the motion affects 

 the whole, without any alternating motion in the particles. 

 For which reason try whether flame do not burn more at 

 the sides than in its centre. 



It is also shown in this, that all burning proceeds by the 

 minute pores of bodies, undermining, penetrating, piercing, 

 and pricking them as if with an infinite number of needle 

 points. Hence all strong acids (if adapted to the body on 

 which they act) exhibit the effects of fire from their cor 

 roding and pungent nature. 



The difference of which we now speak is common also 

 to the nature of cold, in which the contracting motion is 

 restrained by the resistance of expansion, as in heat the 

 expansive motion is restrained by the resistance of con 

 traction. 



Whether, therefore, the particles of matter penetrate in 

 wards or outwards the reasoning is the same, though the 

 power be very different, because we have nothing on earth 

 which is intensely cold. 



IV. The fourth difference is a modification of the pre 

 ceding ; namely, that this stimulating or penetrating motion 

 should be rapid and never sluggish, and should take place 

 not in the very minutest particles, but rather in those of 

 some tolerable dimensions. 



It is shown by comparing the effects of fire with those of 

 time. Time dries, consumes, undermines, and reduces to 

 ashes as well as fire, and perhaps to a much finer degree, 

 but as its motion is very slow, and attacks very minute par 

 ticles, no heat is perceived. 



It is also shown in a comparison of the dissolution of 

 iron and gold. For gold is dissolved without the excite 

 ment of any heat, but iron with a vehement excitement of 

 it, although almost in the same time : because, in the former, 

 the penetration of the separating acid is mild, and gently 

 insinuates itself, and the particles of gold yield easily, but 

 the penetration of iron is violent, and attended with some 

 struggle, and its particles are more obstinate. 



