328 NOVUM ORGANUM. 



motion which is alternative and continually growing strong, and 

 struggling, and irritated by reflection ; whence the fury of fire and 

 heat has its origin. 



This Difference is shown most of all in flame and boiling liquids, 

 which are continually quivering and swelling up in small portions and 

 subsiding again. 



It is shown also in those bodies which are so closely compacted, as 

 not to swell up or be dilated in mass when heated or ignited ; such as 

 iron in a state of ignition, in which the heat is very fierce. 



It is shown also in the fact that a fire burns most briskly in the 

 coldest weather. 



It is shown also in the fact that when air is expanded in a heat- 

 glass, without impediment or repulsion (that is to say, uniformly and 

 equally), no heat is perceived. And also in the case of wind which 

 has been confined, though it breaks out with the greatest violence, 

 still no remarkable heat is perceived, because the motion is of the 

 whole, and without alternating motion in the particles. And on this 

 point let experiment be made whether flame burns more fiercely 

 towards the sides than in the middle. 



It is shown also by the fact that all burning acts on minute pores of 

 the body which is burned; so that the burning undermines, penetrates, 

 pricks, and goads the body, just as if an infinite number of sharp 

 points were at work. And from this it also results, that all strong 

 waters (when suited to the body on which they act) operate like fire, 

 owing to their corrosive and pungent nature. 



And this Difference (of which we now speak) is common also to the 

 Nature of Cold ; in which the contractile motion is restrained by a 

 resistance of expansion, just as in heat the expansive motion is 

 restrained by a resistance of contraction. 



And so, whether parts of a body penetrate towards the interior or 

 towards the exterior, the principle is the same, although the strength 

 put forth is very different ; because we have not here upon the surface 

 of the earth anything which is intensely cold. 



The Fourth Difference is a modification of the foregoing ; it is that 

 this stimulating and penetrating motion must be somewhat rapid, and 

 the reverse of sluggish, and must take place by particles, minute 

 indeed, yet not of an extreme degree of subtlety, but a little larger. 



This Difference is shown by comparing the effects of fire with those 

 of time or age. For age or time dries, consumes, undermines, and 

 reduces to ashes no less than fire, indeed with far more subtlety ; but 

 because motion of this kind is very sluggish, and takes place through 

 particles which are very delicate, no heat is perceived. 



It is also shown by comparing the dissolution of iron with that of 

 gold. For gold is dissolved without exciting heat, and the dissolution 

 of iron takes place with accompaniment of vehement heat, although 

 the time required for effecting it is nearly the same. This is because, in 

 the case of the gold, the water of separation makes its entrance gently, 

 insinuating itself with subtlety, and the particles of the gold yield 



