NOVUM O RCA NUM. 375 



water, in swimming ; air, in flying ; water, in rowing ; air, in the un 

 dulation of winds ; the springs in clocks. And this motion of com 

 pressed air is shown prettily in children s toy guns, which they make 

 by hollowing out a piece of elder or some such wood, and then stuff 

 in a lump of some succulent root, or the like, at each end : they then 

 thrust the pellet of root towards the other opening by means of a 

 ramrod ; on which the piece is driven out and expelled at the other 

 end with a report, and that before it is touched by the neighbouring 

 root or pellet, or by the ramrod. And as to liberation from tension, 

 this motion shows itself in the air which remains after the exhaustion 

 of ghiss eggs ; and in strings, leather, cloth, which recoil after tension, 

 unless it has become too strong by continuance, &c. And this motion 

 the Schoolmen indicate under the name of Motion &quot; from the Form 

 of Element ; &quot; unskilfully enough, as this motion pertains not only to 

 air, water, or flame, but to all substances possessing consistency, how 

 ever diverse : as wood, iron, lead, cloths, skins, &c., in which each 

 body has its own measure of dimensions, and is with difficulty ex 

 tended into any other appreciable space. Hut because this motion of 

 liberty is the most obvious of all, and of infinite application, it would 

 be wise to distinguish it well and clearly. For some very carelessly 

 confound this motion with the two motions of resistance and connec 

 tion ; that is to say, the liberation from pressure with the motion of 

 resistance ; the liberation from tension with the motion of connec 

 tion ; as if bodies, when compressed, yielded or expanded, to prevent 

 a penetration of dimensions; and bodies under tension recoiled and 

 contracted to prevent the formation of a vacuum. But if air, when 

 compressed, were to contract till it became dense as water, or wood 

 till it became dense as stone, there would be no occasion for a pene 

 tration of dimensions ; and yet the compression would be far greater 

 than they ever endure. In the same way, if water were to expand 

 till it became as rare as air, or stone till it became rare as wood, there 

 would be no need of a vacuum, and yet the degree of extension would 

 be far greater than they ever endure. So the question does not 

 become one of penetration of dimensions, or of a vacuum, except in 

 the extreme limits of condensation and rarefaction ; while the motions 

 of which we speak stop short far within these limits : and are nothing 

 but the desire of bodies to preserve their consistency (or, if it be 

 preferred, their Forms), and not to recede from them hastily, nor to be 

 altered, save by gentle means and by their own consent. Now it is 

 far more necessary for men to be told (inasmuch as it carries with it 

 great results) that the violent motion (which we call mechanical, but 

 which Dcmocritus, who, in explaining his prime motions, must be set 

 far below even middling philosophers, called Motion of a Stroke) is 

 merely the Motion of Liberty, that is to say, from compression to 

 relaxation. For in all simple protrusion or flight through air, there is 

 no displacing or motion in space, before the parts of the body arc 

 unnaturally acted upon and compressed by the impelling force. Then 

 each part pushing the other in succession, the whole is carried along, 

 not only with a progressive, but also with a rotatory motion, the parts 



