stand, but are borne down by their weight; so that very high buildings must incline to a pyramidal form, and be narrower towards the top. But what that nature is which increases or lessens this desire of continuity will not easily be found on inquiry. It will perhaps be suggested that the parts of solids are denser and more compact; the parts of liquids rarer and looser; or that liquids have a spirit which is a principle of fluidity that is wanting in solids, and the like. But neither of these is in accordance with truth. For it is manifest that snow and wax, which may be cut and moulded and take impressions, are far rarer than quicksilver or melted lead, as is proved in the proportion of their gravities. But if a man still insist that snow or wax, though rarer (in the whole) than quicksilver, may yet have closer and more compact parts; but that because their bodies are spongy, and have many cavities, and admit the air, they are therefore in the whole lighter; as is the case in the pumice-stone, which in proportion to its size may perhaps be lighter than wood, yet if both be reduced to powder, the powder of pumice-stone will be heavier than that of wood, because it has now lost its cavities; his observations and objections are good. But what will they say to melted snow and wax, where the cavities are already filled up? or what to the bodies of gums, mastich, and the like, which have not these manifest cavities, and yet are lighter than many fluids? Now what they allege of the spirit, the power and force whereof make things flow, is certainly at first sight probable, and familiar to common notions; but in reality it is more difficult and erroneous, as being not only not supported by reason, but almost opposed to it. For this spirit they talk of does in fact (though it may appear strange) produce consistency, and not fluidity. And this is excellently shown in the instance of snow, which though a body compounded of water and air, and though air and water separate are fluids, yet acquires consistency by mixture. But if a man object that this may perhaps proceed from a condensation of the watery part by cold, and not from the interposition of the air, he may correct his opinion by observing that foam also is a body like snow, which yet is no way condensed by cold. But if he still urge that in foam likewise condensation proceeds not from cold, but from agitation and percussion, let him look at the boys who, out of a little air breathed through a pipe or tube,

and water mixed with a little soap, to make it more tenacious, raise a wonderful tower-like fabric of bubbles. But the fact is that bodies, at the touch of a body that is friendly or similar, resolve and open themselves; but at the touch of an unfriendly body they shrink up and gather themselves together. And hence the apposition of an alien body is the cause of consistency. Thus we see that when oil is mixed with water, the transparency which existed before both in the oil and the water is to a certain extent lost. On the other hand, we see that paper moistened with water resolves itself and loses its consistency (which before by reason of the air in its pores was strong); but moistened with oil it does it less, because oil agrees less with paper. The same likewise we see in sugar and like bodies, which relax themselves to receive water or wine, and that not only when the liquids press upon them, but they likewise suck and draw up the liquids themselves.

VII.

On the Consent between Sensible and Insensible Bodies.

of

The passions of bodies which have sense, and of bodies without sense, have a great correspondence, except that a sensible body has also a spirit. For the pupil of the eye is like a looking-glass, or water, and receives and reflects the images of light and visible bodies in the same manner. The organ hearing has a conformity with an obstruction in a cave, from which the voice and sound is best re-echoed. The attraction of things inanimate, and again the horrors and aversions (I speak of such as are proper and peculiar) in animals, correspond to the sense of smell and pleasing and disagreeable odours. In the taste and touch we find every kind either of violence on the one hand or of gentle and friendly insinuation on the other which can happen in inanimate bodies, with all the configurations of these same passions, expressed and interpreted. For in dead bodies compressions, extensions, corrosions, separations, and the like are concealed in their process, and only perceived in their manifest effects. But in animals they are performed with a sensation of pain, according to the different kind and character of the violence, the spirit pervading everything. And from this principle is derived the knowledge whether any animal may possibly have some other sense besides those observed; and how

many, and what kind of senses there may be in the whole race of animals. For a just distinction of the passions of matter will give the number of senses, provided only that the requisite organs be supplied, and the spirit be added.

VIII.

On Violent Motion, that it is the flight and dispersion of the parts of a thing from pressure, though not visible.

Violent motion (as they call it), whereby projectiles, as stones, arrows, bullets, and the like, fly through the air, is about the commonest of all motions. And yet in the observation and inquisition hereof men have shown a strange supineness and negligence; nor is it a small loss that is entailed by miscarriage in the investigation of the nature and power of this motion; seeing it is of use in infinite ways, and as the life and soul of artillery, engines, and the whole business of mechanics. Now most inquirers, when they have pronounced this motion to be violent, and distinguished it from natural motion, think they have done. And it is indeed the peculiar manner and discipline of Aristotle and his school, to teach men what to say, not what to think; and how to discharge themselves by affirming or denying, not how to explain and satisfy themselves in thought. Others use a little more diligence, and taking up the position that two bodies cannot be in the same place, conclude that the stronger impels, and the weaker gives way; that this giving way or flight, if the force applied be small, does not continue after the cessation of the first impulse, as in protrusion; but that if the force be great, it continues for a time even after the removal of the impelling body, till it is gradually diminished, as in throwing. And these again, after another inveterate habit of the same school, catch at the beginnings of things, but do not trouble themselves about their process and end; as if every beginning implied the rest; and hence, in a kind of premature impatience, they break off the inquiry. For upon the point that bodies yield at the instant of the stroke, they have something to say; but why, after the impelling body has been removed, and the necessity for the disarrangement of the bodies has thereby absolutely ceased, the motion should still continue, they say nothing, nor do they clearly understand themselves. Others, more diligent and perseverant in inquiry, having ob

served the power of the air in winds, and the like, which is so great that it can even blow down trees and towers, imagined that the force which carries and accompanies projectiles after the first impulse should be attributed to the air collecting itself and rushing in behind the body moved, by which force the body is carried forward like a ship in the water. And these certainly keep to the point, and carry their speculation to its issue; yet they fail of the truth. Now the case is really this. The principal motion seems to be in the parts of the body projected, which being too subtle to be perceived by the eye, and men not being attentive enough but passing the matter by with a light observation, is not observed. But to an accurate observer it is manifest that hard bodies are most impatient of pressure, and have, as it were, a very acute perception thereof; so that when forced ever so little out of their natural position, they strive with great velocity to free themselves and return to their former state. And to do this, all the parts, commencing with the part struck, thrust and press one another forward, just like an external force; which produces a continuous and intense (though invisible) trepidation and commotion of the parts. And this we see in glass, sugar, and brittle things of the like nature; which, if they be cut or divided with any sharp iron instrument, directly and almost instantaneously break to pieces in other places untouched by the stroke of the instrument; which plainly proves that the motion of pressure is communicated to the neighbouring parts; which motion, working all round, and making trial everywhere, causes fracture in that part, where from the predisposition of the body the union was weakest; and yet this very motion, while it disturbs and penetrates every part, does not show itself to the eye until there is an open fracture or solution of continuity. Again, we see if a piece of iron wire, or a stick, or a quill (or such like bodies as are flexible and yet elastic) be bent, and held by both ends between the finger and thumb, it immediately leaps away. Now the cause of this motion is proved manifestly not to lie in the extreme parts of the body, which are held fast by the fingers; but in the middle, which bears the violence; to relieve which this motion is set at work. But in this example it plainly appears that the cause of motion they derive from the impulse of the air is excluded; for there is no percussion to set the air in action. And this is also shown in

the trivial experiment of squeezing a fresh and slippery plumstone between the fingers, gradually increasing the pressure, and so shooting it out. For in this example likewise, compression takes the place of percussion. But the most evident effect of this motion is seen in the perpetual revolutions or rotations of projectiles in their flight; for they go forward, but their progress is in spiral lines,—that is, revolving as they go. And certainly I have felt some doubt as to this spiral motion, so rapid as it is and yet so free and as it were familiar to things, whether it did not depend on some higher principle. But I think the cause of this effect is the same that I am now speaking of, and no other. For pressure of a body at once excites a motion in the parts or particles to extricate and free themselves in any way they

And hence the body is not only driven in a straight line, and so flies forward; but it tries all round, and therefore revolves; for both motions help to set it free. And in solid bodies this is something subtle and abstruse; in soft bodies it is evident, and almost palpable. For as wax or lead, and similar soft bodies, on being struck with a hammer, give way not only forwards, but on all sides; so hard or resisting bodies fly both in a right line and round about. For the corporeal yielding in soft bodies and the local yielding in hard proceed on the same principle; and it is in the change of shape of a soft body that we can best perceive what the passion of a hard body is when it escapes and flies. Meantime, I would not be understood to deny that, besides this motion (which is the principal thing), some part of the work is also to be attributed to the conveyance of the air, by which the principal motion may be assisted, impeded, turned, and directed. For of this too the power is not inconsiderable. And this explanation of violent and mechanical motion (which has hitherto escaped observation) is as the fountain of practical operation.

IX.

On the cause of Motion in Fire-arms, that it has only been inquired in part, and that not the principal one.

The cause of fire-arms, and the explanation of so powerful and noble a motion is imperfect, and deficient in the most important part. For they say that gunpowder, when con