260 NOVUM ORGANUM 



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 last two; 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 light 

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

 importance to the 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, 

 although 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 former 

 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, colors and all its other images disap 

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

 vibration of the body, sound soon fails, and although 



