NOVUM ORGANUM. 191 



therefore, is excited much less rapidly and readily in stone 

 or metal, than in air, on account of the inaptitude and 

 sluggishness of those bodies in acquiring that motion, so 

 that it is probable, that there may be some substances, 

 towards the centre of the earth, quite incapable of being 

 heated, on account of their density, which may deprive 

 them of the spirit by \vhich the motion of excitement is 

 usually commenced. Thus also the magnet creates in the 

 iron a new disposition of its parts, and a conformable motion 

 without losing any of its virtue. So the leaven of bread, 

 yeast, rennet, and some poisons, excite and invite succes 

 sive and continued motion in dough, beer, cheese, or the 

 human body ; not so much from the power of the exciting, 

 as the predisposition and yielding of the excited body. 



Let the thirteenth motion be that of impression, which 

 is also a species of motion of assimilation, and the most 

 subtile of diffusive motions. We have thought it right, 

 however, to consider it as a distinct species, on account of 

 its remarkable difference from the two last. For the simple 

 motion of assimilation transforms the bodies themselves, so 

 that if you remove the first agent, you diminish not the effect 

 of those which succeed ; thus, neither the first lighting of 

 flame, nor the first conversion into air, are of any impor 

 tance to the &quot;flame or air next generated. So, also, the 

 motion of excitement still continues for a considerable time 

 after the removal of the first agent, as in a heated body 

 on the removal of the original heat, in the excited iron 

 on the removal of the magnet, and in the dough on the 

 removal of the leaven. But the motion of impression, al 

 though diffusive and transitive, appears, nevertheless, to 

 depend on the first agent, so that upon the removal of the 

 latter the former immediately fails and perishes ; for which 

 reason also it takes effect in a moment, or at least a very 

 short space of time. We are wont to call the two formeV 

 motions the motions of the generation of Jupiter, because 

 when born they continue to exist ; and the latter, the mo 

 tion of the generation of Saturn, because it is immediately 

 devoured and absorbed. It may be seen in three instances 

 1. in the rays of light; 2. in the percussions of sounds ; 3. 

 in magnetic attractions as regards communication. For, on 

 the removal of light, colours and all its other images disap 

 pear, as on the cessation of the first percussion and the vi 

 bration of the body sound soon fails; and although sounds 

 are agitated by the wind, like waves, yet it is to be observed, 

 that the same sound does not last during the whole time of 

 the reverberation. Thus, when a bell is struck, the sound 



