NOVUM ORGANUM 247 



if it be preferred, their form), and not to desert them sud 

 denly, but only to change by degrees, and of their own 

 accord. It is, however, much more necessary to intimate 

 to mankind (because many other points depend upon this), 

 that the violent motion which we call mechanical, and 

 Democritus (who, in explaining his primary motions, is 

 to be ranked even below the middling class of philoso 

 phers) termed the motion of a blow, is nothing else than 

 this motion of liberty, namely, a tendency to relaxation 

 from compression. For in all simple impulsion or flight 

 through the air, the body is not displaced or moved in 

 space, until its parts are placed in an unnatural state, and 

 compressed by the impelling force. When that takes 

 place, the different parts urging the other in succes 

 sion, the whole is moved, and that with a rotatory as 

 well as progressive motion, in order that the parts may, 

 by this means also, set themselves at liberty, or more 

 readily submit. Let this suffice for the motion in 

 question. 



Let the fourth be that which we term the motion of mat 

 ter, and which is opposed to the last; for in the motion of 

 liberty, bodies abhor, reject, and avoid a new size or vol 

 ume, or any new expansion or contraction (for these differ 

 ent terms have the same meaning), and strive, with all their 

 power, to rebound and resume their former density; on the 

 contrary, in the motion of matter, they are anxious to ac 

 quire a new volume or dimension, and attempt it willingly 

 and rapidly, and occasionally by a most vigorous effort, as 

 in the example of gunpowder. The most powerful, or at 

 least most frequent, though not the only instruments of 

 this motion, are heat and cold. For instance, the air, if 

 expanded by tension (as by suction in the glass egg), strug- 



