NOVUM ORGAXUM. 181 



delighting, as it were, in the mutual connexion and con 

 tact. This is called by the schools a motion &quot; to prevent 

 a vacuum.&quot; It takes place when water is drawn up by 

 suction or a syringe, the flesh by cupping, or when the 

 water remains without esca ping from perforated jars, unless 

 the mouth be opened to admit the air, and innumerable in 

 stances of a like nature. 



Let the third be that which we term the motion of li 

 berty ; by which bodies strive to deliver themselves from 

 any unnatural pressure or tension, and to restore them 

 selves to the dimensions suited to their mass; and of 

 which also there are innumerable examples. Thus we have 

 examples of their escaping from pressure, in the water in 

 swimming, in the air in flying, in the water again in row 

 ing, and in the air in the undulation of the winds, and in 

 springs of watches. An exact instance of the motion 

 of compressed air is seen in children s popguns, which 

 they make by scooping out elder branches or some such 

 matter, and forcing: in a piece of some pulpy root or the 

 like, at each end ; then they force the root or other pellet 

 with a ramrod to the opposite end, from which the lower 

 pellet is emitted and projected with a report, and that be 

 fore it is touched by the other piece of root or pellet, or by 

 the ramrod. We have examples of their escape from tension, 

 in the motion of the air that remains in glass eggs after suc 

 tion, in strings, leather, and cloth, which recoil after tension, 

 unless it be long continued. The schools define this by 

 the term of motion &quot; from the form of the element ;&quot; injudi 

 ciously enough, since this motion is to be found not only in 

 air, water, or fire, but in every species of solid, as wood, iron, 

 lead, cloth, parchment, &c. each of which has its own proper 

 size, and is with difficulty stretched to any other. Since, 

 however, this motion of liberty is the most obvious of all, and 

 to be seen in an infinite number of cases, it will be as well 

 to distinguish it correctly and clearly ; for some most care 

 lessly confound this with the two others of resistance and 

 connexion ; namely, the freedom from pressure with the 

 former, and that from tension with the latter; as if bodies 

 when compressed yielded or expanded to prevent a pene 

 tration of dimensions, and when stretched rebounded and 

 contracted themselves to prevent a vacuum. But if the air, 

 when compressed, could be brought to the density of water, 

 or wood to that of stone, there would be no need of any 

 penetration of dimensions, and yet the compression would 

 be much greater than they actually admit of. So if water 

 could be expanded till it became as rare as air, or stone as 



