Chapter XXVIII (1)

OF COLD, WIND, HARD, ICE, RESTITUTION OF
BODIES BENT, DIAPHANOUS, LIGHTNING AND
THUNDER; AND OF THE HEADS OF RIVERS.

1. Why breath from the same mouth sometimes heats and sometimes
cools.—2. Wind, and the inconstancy of winds, whence.—3 Why there is
a constant, though not a great wind, from east to west, near the
equator.—4. What is the effect of air pent in between the clouds.—5.
No change from soft to hard, but by motion.—6. What is the cause of
cold near the poles.—7.. The cause of ice; and why the cold is more
remiss in rainy than in clear weather. Why water doth not freeze in
deep wells as it doth near the superficies of the earth. Why ice is
not so heavy as water; and why wine is not so easily frozen as
water.—8. Another cause of hardness from the fuller contact of
atoms; also, how hard things are broken.—9. A third cause of
hardness from heat.—10. A fourth cause of hardness from the motion
of atoms enclosed in a narrow space.—11. How hard things are
softened.—12. Whence proceed the spontaneous restitution of things
bent.—13. Diaphanous and opacous, what they are, and whence.—14. The
cause of lightning and thunder.—15. Whence it proceeds that clouds
can fall again after they are once elevated and frozen.—16. How it
could be that the moon was eclipsed, when she was not diametrically
opposite to the sun.—17. By what means many suns may appear at
once.—18. Of the heads of rivers.

[Sidenote: Why breath from the same mouth sometimes heats and sometimes
cools.]

1. As, when the motion of the ambient ethereal substance makes the spirits and fluid parts of our bodies tend outwards, we acknowledge heat; so, by the endeavour inwards of the same spirits and humours, we feel cold. So that to cool is to make the exterior parts of the body endeavour inwards, by a motion contrary to that of calefaction, by which the internal parts are called outwards. He, therefore, that would know the cause of cold, must find by what motion or motions the exterior parts of any body endeavour to retire inwards. To begin with those phenomena which are the most familiar. There is almost no man but knows, that breath blown strongly, and which comes from the mouth with violence, that is to say, the passage being strait, will cool the hand; and that the same breath blown gently, that is to say, through a greater aperture, will warm the same. The cause of which phenomenon may be this, the breath going out hath two motions; the one, of the whole and direct, by which the foremost parts of the hand are driven inwards; the other, simple motion of the small particles of the same breath, which, (as I have shown in the 3rd article of the last chapter, causeth heat. According, therefore, as either of these motions is predominant, so there is the sense sometimes of cold, sometimes of heat. Wherefore, when the breath is softly breathed out at a large passage, that simple motion which causeth heat prevaileth, and consequently heat is felt; and when, by compressing the lips, the breath is more strongly blown out, then is the direct motion prevalent, which makes us feel cold. For, the direct motion of the breath or air is wind; and all wind cools or diminisheth former heat.

[Sidenote: Wind, and the inconstancy of winds, whence.]

2. And seeing not only great wind, but almost any ventilation and stirring of the air, doth refrigerate; the reason of many experiments concerning cold cannot well be given without finding first what are the causes of wind. Now, wind is nothing else but the direct motion of the air thrust forwards; which, nevertheless, when many winds concur, may be circular or otherwise indirect, as it is in whirlwinds. Wherefore, in the first place we are to enquire into the causes of winds. Wind is air moved in a considerable quantity, and that either in the manner of waves, which is both forwards and also up and down, or else forwards only.

Supposing, therefore, the air both clear and calm for any time how little soever, yet, the greater bodies of the world being so disposed and ordered as has been said, it will be necessary that a wind presently arise somewhere. For, seeing that motion of the parts of the air, which is made by the simple motion of the sun in his own epicycle, causeth an exhalation of the particles of water from the seas and all other moist bodies, and those particles make clouds; it must needs follow, that, whilst the particles of water pass upwards, the particles of air, for the keeping of all spaces full, be jostled out on every side, and urge the next particles, and these the next; till having made their circuit, there comes continually so much air to the hinder parts of the earth as there went water from before it. Wherefore, the ascending vapours move the air towards the sides every way; and all direct motion of the air being wind, they make a wind. And if this wind meet often with other vapours which arise in other places, it is manifest that the force thereof will be augmented, and the way or course of it changed. Besides, according as the earth, by its diurnal motion, turns sometimes the drier, sometimes the moister part towards the sun, so sometimes a greater, sometimes a less, quantity of vapours will be raised; that is to say, sometimes there will be a less, sometimes a greater wind. Wherefore, I have rendered a possible cause of such winds as are generated by vapours; and also of their inconstancy.

From hence it follows that these winds cannot be made in any place, which is higher than that to which vapours may ascend. Nor is that incredible which is reported of the highest mountains, as the Peak of Teneriffe and the Andes of Peru, namely, that they are not at all troubled with these inconstant winds. And if it were certain that neither rain nor snow were ever seen in the highest tops of those mountains, it could not be doubted but that they are higher than any place to which vapours use to ascend.

[Sidenote: Why there is a constant, though not a great wind, from east
to west, near the equator.]

3. Nevertheless, there may be wind there, though not that which is made by the ascent of vapours, yet a less and more constant wind, like the continued blast of a pair of bellows, blowing from the east. And this may have a double cause; the one, the diurnal motion of the earth; the other, its simple motion in its own epicycle. For these mountains being, by reason of their height, more eminent than all the rest of the parts of the earth, do by both these motions drive the air from the west eastwards. To which, though the diurnal motion contribute but little, yet seeing I have supposed that the simple motion of the earth, in its own epicycle, makes two revolutions in the same time in which the diurnal motion makes but one, and that the semidiameter of the epicycle is double to the semidiameter of the diurnal conversion, the motion of every point of the earth in its own epicycle will have its velocity quadruple to that of the diurnal motion; so that by both these motions together, the tops of those hills will sensibly be moved against the air; and consequently a wind will be felt. For whether the air strike the sentient, or the sentient the air, the perception of motion will be the same. But this wind, seeing it is not caused by the ascent of vapours, must necessarily be very constant.

[Sidenote: What is the effect of air pent in between the clouds.]

4. When one cloud is already ascended into the air, if another cloud ascend towards it, that part of the air, which is intercepted between them both, must of necessity be pressed out every way. Also when both of them, whilst the one ascends and the other either stays or descends, come to be joined in such manner as that the ethereal substance be shut within them on every side, it will by this compression also go out by penetrating the water. But in the meantime, the hard particles, which are mingled with the air and are agitated, as I have supposed, with simple motion, will not pass through the water of the clouds, but be more straitly compressed within their cavities. And this I have demonstrated at the 4th and 5th articles of chapter XXII. Besides, seeing the globe of the earth floateth in the air which is agitated by the sun's motion, the parts of the air resisted by the earth will spread themselves every way upon the earth's superficies; as I have shown at the 8th article of chapter XXI.

[Sidenote: No change from soft to hard, but by motion.]

5. We perceive a body to be hard, from this, that, when touching it, we would thrust forwards that part of the same which we touch, we cannot do it otherwise than by thrusting forwards the whole body. We may indeed easily and sensibly thrust forwards any particle of the air or water which we touch, whilst yet the rest of its parts remain to sense unmoved. But we cannot do so to any part of a stone. Wherefore I define a _hard_ body to be that whereof no part can be sensibly moved, unless the whole be moved. Whatsoever therefore is soft or fluid, the same can never be made hard but by such motion as makes many of the parts together stop the motion of some one part, by resisting the same.

[Sidenote: What it the cause of cold near the poles.]

6. Those things premised, I shall show a possible cause why there is greater cold near the poles of the earth, than further from them. The motion of the sun between the tropics, driving the air towards that part of the earth's superficies which is perpendicularly under it, makes it spread itself every way; and the velocity of this expansion of the air grows greater and greater, as the superficies of the earth comes to be more and more straitened, that is to say, as the circles which are parallel to the equator come to be less and less. Wherefore this expansive motion of the air drives before it the parts of the air, which are in its way, continually towards the poles more and more strongly, as its force comes to be more and more united, that is to say, as the circles which are parallel to the equator are less and less; that is, so much the more, by how much they are nearer to the poles of the earth. In those places, therefore, which are nearer to the poles, there is greater cold than in those which are more remote from them. Now this expansion of the air upon the superficies of the earth, from east to west, doth, by reason of the sun's perpetual accession to the places which are successively under it, make it cold at the time of the sun's rising and setting; but as the sun comes to be continually more and more perpendicular to those cooled places, so by the heat, which is generated by the supervening simple motion of the sun, that cold is again remitted; and can never be great, because the action by which it was generated is not permanent. Wherefore I have rendered a possible cause of cold in those places that are near the poles, or where the obliquity of the sun is great.

[Sidenote: The cause of ice; and why the cold is more remiss in rainy
than in clear weather. Why water doth not freeze in deep
wells, as it doth near the superficies of the earth. Why ice
is not so heavy as water; and why wine is not so easily
frozen as water.]

7. How water may be congealed by cold, may be explained in this manner. Let A (in figure 1) represent the sun, and B the earth. A will therefore be much greater than B. Let E F be in the plane of the equinoctial; to which let G H, I K, and L C be parallel. Lastly, let C and D be the poles of the earth. The air, therefore, by its action in those parallels, will rake the superficies of the earth; and that with motion so much the stronger, by how much the parallel circles towards the poles grow less and less. From whence must arise a wind, which will force together the uppermost parts of the water, and withal raise them a little, weakening their endeavour towards the centre of the earth. And from their endeavour towards the centre of the earth, joined with the endeavour of the said wind, the uppermost parts of the water will be pressed together and coagulated, that is to say, the top of the water will be skinned over and hardened. And so again, the water next the top will be hardened in the same manner, till at length the ice be thick. And this ice, being now compacted of little hard bodies, must also contain many particles of air received into it.

As rivers and seas, so also in the same manner may the clouds be frozen. For when, by the ascending and descending of several clouds at the same time, the air intercepted between them is by compression forced out, it rakes, and by little and little hardens them. And though those small drops, which usually make clouds, be not yet united into greater bodies, yet the same wind will be made; and by it, as water is congealed into ice, so will vapours in the same manner be congealed into snow. From the same cause it is that ice may be made by art, and that not far from the fire. For it is done by the mingling of snow and salt together, and by burying in it a small vessel full of water. Now while the snow and salt, which have in them a great deal of air, are melting, the air, which is pressed out every way in wind, rakes the sides of the vessel; and as the wind by its motion rakes the vessel, so the vessel by the same motion and action congeals the water within it.

We find by experience, that cold is always more remiss in places where it rains, or where the weather is cloudy, things being alike in all other respects, than where the air is clear. And this agreeth very well with what I have said before. For in clear weather, the course of the wind which, as I said even now, rakes the superficies of the earth, as it is free from all interruption, so also it is very strong. But when small drops of water are either rising or falling, that wind is repelled, broken, and dissipated by them; and the less the wind is, the less is the cold.

We find also by experience, that in deep wells the water freezeth not so much as it doth upon the superficies of the earth. For the wind, by which ice is made, entering into the earth by reason of the laxity of its parts, more or less, loseth some of its force, though not much. So that if the well be not deep, it will freeze; whereas if it be so deep, as that the wind which causeth cold cannot reach it, it will not freeze.

We find moreover by experience, that ice is lighter than water. The cause whereof is manifest from that which I have already shown, namely, that air is received in and mingled with the particles of the water whilst it is congealing.

Lastly, wine is not so easily congealed as water, because in wine there are particles, which, being not fluid, are moved very swiftly, and by their motion congelation is retarded. But if the cold prevail against this motion, then the outermost parts of the wine will be first frozen, and afterwards the inner parts; whereof this is a sign, that the wine which remains unfrozen in the midst will be very strong.

[Sidenote: Another cause of hardness from the fuller contact of atoms.
Also how hard things are broken.]

8. We have seen one way of making things hard, namely, by congelation. Another way is thus. Having already supposed that innumerable atoms, some harder than others and that have several simple motions of their own, are intermingled with the ethereal substance; it follows necessarily from hence, that by reason of the fermentation of the whole air, of which I have spoken in chapter XXI, some of those atoms meeting with others will cleave together, by applying themselves to one another in such manner as is agreeable to their motions and mutual contacts; and, seeing there is no vacuum, cannot be pulled asunder, but by so much force as is sufficient to overcome their hardness.

Now there are innumerable degrees of hardness. As for example, there is a degree of it in water, as is manifest from this, that upon a plane it may be drawn any way at pleasure by one's finger. There is a greater degree of it in clammy liquors, which, when they are poured out, do in falling downwards dispose themselves into one continued thread; which thread, before it be broken, will by little and little diminish its thickness, till at last it be so small, as that it seems to break only in a point; and in their separation the external parts break first from one another, and then the more internal parts successively one after another. In wax there is yet a greater degree of hardness. For when we would pull one part of it from another, we first make the whole mass slenderer, before we can pull it asunder. And how much the harder anything is which we would break, so much the more force we must apply to it. Wherefore, if we go on to harder things, as ropes, wood, metals, stones, &c., reason prompteth us to believe that the same, though not always sensibly, will necessarily happen; and that even the hardest things are broken asunder in the same manner, namely, by solution of their continuity begun in the outermost superficies, and proceeding successively to the innermost parts. In like manner, when the parts of bodies are to be separated, not by pulling them asunder, but by breaking them, the first separation will necessarily be in the convex superficies of the bowed part of the body, and afterwards in the concave superficies. For in all bowing there is in the convex superficies an endeavour in the parts to go one from another, and in the concave superficies to penetrate one another.

This being well understood, a reason may be given how two bodies, which are contiguous in one common superficies, may by force be separated without the introduction of vacuum; though Lucretius thought otherwise, believing that such separation was a strong establishment of vacuum. For a marble pillar being made to hang by one of its bases, if it be long enough, it will by its own weight be broken asunder; and yet it will not necessarily follow that there should be vacuum, seeing the solution of its continuity may begin in the circumference, and proceed successively to the midst thereof.

[Sidenote: A third cause of hardness, from heat.]

9. Another cause of hardness in some things may be in this manner. If a soft body consist of many hard particles, which by the intermixture of many other fluid particles cohere but loosely together, those fluid parts, as hath been shown in the last article of chapter XXI, will be exhaled; by which means each hard particle will apply itself to the next to it according to a greater superficies, and consequently they will cohere more closely to one another, that is to say, the whole mass will be made harder.

[Sidenote: A fourth cause of hardness, from the motion of atoms enclosed
in a narrow space.]

10. Again, in some things hardness may be made to a certain degree in this manner. When any fluid substance hath in it certain very small bodies intermingled, which, being moved with simple motion of their own, contribute like motion to the parts of the fluid substance, and this be done in a small enclosed space, as in the hollow of a little sphere, or a very slender pipe, if the motion be vehement and there be a great number of these small enclosed bodies, two things will happen; the one, that the fluid substance will have an endeavour of dilating itself at once every way; the other, that if those small bodies can nowhere get out, then from their reflection it will follow, that the motion of the parts of the enclosed fluid substance, which was vehement before, will now be much more vehement. Wherefore, if any one particle of that fluid substance should be touched and pressed by some external movent, it could not yield but by the application of very sensible force. Wherefore the fluid substance, which is enclosed and so moved, hath some degree of hardness. Now, greater and less degree of hardness depends upon the quantity and velocity of those small bodies, and upon the narrowness of the place both together.

[Sidenote: How hard things are softened.]

11. Such things as are made hard by sudden heat, namely such as are hardened by fire, are commonly reduced to their former soft form by maceration. For fire hardens by evaporation, and therefore if the evaporated moisture be restored again, the former nature and form is restored together with it. And such things as are frozen with cold, if the wind by which they were frozen change into the opposite quarter, they will be unfrozen again, unless they have gotten a habit of new motion or endeavour by long continuance in that hardness. Nor is it enough to cause thawing, that there be a cessation of the freezing wind; for the taking away of the cause doth not destroy a produced effect; but the thawing also must have its proper cause, namely, a contrary wind, or at least a wind opposite in some degree. And this we find to be true by experience. For, if ice be laid in a place so well enclosed that the motion of the air cannot get to it, that ice will remain unchanged, though the place be not sensibly cold.

[Sidenote: Whence proceeds the spontaneous restitution of things bent.]

12. Of hard bodies, some may manifestly be bowed; others not, but are broken in the very first moment of their bending. And of such bodies as may manifestly be bended, some being bent, do, as soon as ever they are set at liberty, restore themselves to their former posture; others remain still bent. Now if the cause of this restitution be asked, I say, it may be in this manner, namely, that the particles of the bended body, whilst it is held bent, do nevertheless retain their motion; and by this motion they restore it as soon as the force is removed by which it was bent. For when any thing is bent, as a plate of steel, and, as soon as the force is removed, restores itself again, it is evident that the cause of its restitution cannot be referred to the ambient air; nor can it be referred to the removal of the force by which it was bent; for in things that are at rest the taking away of impediments is not a sufficient cause of their future motion; there being no other cause of motion, but motion. The cause therefore of such restitution is in the parts of the steel itself. Wherefore, whilst it remains bent, there is in the parts, of which it consisteth, some motion though invisible; that is to say, some endeavour at least that way by which the restitution is to be made; and therefore this endeavour of all the parts together is the first beginning of restitution; so that the impediment being removed, that is to say, the force by which it was held bent, it will be restored again. Now the motion of the parts, by which this done, is that which I called simple motion, or motion returning into itself. When therefore in the bending of a plate the ends are drawn together, there is on one side a mutual compression of the parts; which compression is one endeavour opposite to another endeavour: and on the other side a divulsion of the parts. The endeavour therefore of the parts on one side tends to the restitution of the plate from the middle towards the ends; and on the other side, from the ends towards the middle. Wherefore the impediment being taken away, this endeavour, which is the beginning of restitution, will restore the plate to its former posture. And thus I have given a possible cause why some bodies, when they are bent, restore themselves again; which was to be done.

As for stones, seeing they are made by the accretion of many very hard particles within the earth; which particles have no great coherence, that is to say, touch one another in small latitude, and consequently admit many particles of air; it must needs be that, in bending of them, their internal parts will not easily be compressed, by reason of their hardness. And because their coherence is not firm, as soon as the external hard particles are disjoined, the ethereal parts will necessarily break out, and so the body will suddenly be broken.

[Sidenote: Diaphanous and opacous, what they are, and whence.]

13. Those bodies are called _diaphanous_, upon which, whilst the beams of a lucid body do work, the action of every one of those beams is propagated in them in such manner, as that they still retain the same order amongst themselves, or the inversion of that order; and therefore bodies, which are perfectly diaphanous, are also perfectly homogeneous. On the contrary, an _opacous_ body is that, which, by reason of its heterogeneous nature, doth by innumerable reflections and refractions in particles of different figures and unequal hardness, weaken the beams that fall upon it before they reach the eye. And of diaphanous bodies, some are made such by nature from the beginning; as the substance of the air, and of the water, and perhaps also some parts of stones, unless these also be water that has been long congealed. Others are made so by the power of heat, which congregates homogeneous bodies. But such, as are made diaphanous in this manner, consist of parts which were formerly diaphanous.

[Sidenote: The cause of lightning and thunder.]

14. In what manner clouds are made by the motion of the sun, elevating the particles of water from the sea and other moist places, hath been explained in chapter XXVI. Also how clouds come to be frozen, hath been shown above at the 7th article. Now from this, that air may be enclosed as it were in caverns, and pent together more and more by the meeting of ascending and descending clouds, may be deduced a possible cause of _thunder_ and _lightning_. For seeing the air consists of two parts, the one ethereal, which has no proper motion of its own, as being a thing divisible into the least parts; the other hard, namely, consisting of many hard atoms, which have every one of them a very swift simple motion of its own: whilst the clouds by their meeting do more and more straiten such cavities as they intercept, the ethereal parts will penetrate and pass through their watery substance; but the hard parts will in the meantime be the more thrust together, and press one another; and consequently, by reason of their vehement motions, they will have an endeavour to rebound from each other. Whensoever, therefore, the compression is great enough, and the concave parts of the clouds are, for the cause I have already given, congealed into ice, the cloud will necessarily be broken; and this breaking of the cloud produceth the first clap of thunder. Afterwards the air, which was pent in, having now broken through, makes a concussion of the air without, and from hence proceeds the roaring and murmur which follows; and both the first clap and the murmur that follows it make that noise which is called _thunder_. Also, from the same air breaking through the clouds and with concussion falling upon the eye, proceeds that action upon our eye, which causeth in us a perception of that light, which we call _lightning_. Wherefore I have given a possible cause of thunder and lightning.

[Sidenote: Whence it proceeds that clouds can fall again, after they are
once elevated and frozen.]

15. But if the vapours, which are raised into clouds, do run together again into water or be congealed into ice, from whence is it, seeing both ice and water are heavy, that they are sustained in the air? Or rather, what may the cause be, that being once elevated, they fall down again? For there is no doubt but the same force which could carry up that water, could also sustain it there. Why therefore being once carried up, doth it fall again? I say it proceeds from the same simple motion of the sun, both that vapours are forced to ascend, and that water gathered into clouds is forced to descend. For in chapter XXI, article 11, I have shown how vapours are elevated; and in the same chapter, article 5, I have also shown how by the same motion homogeneous bodies are congregated, and heterogeneous dissipated; that is to say, how such things, as have a like nature to that of the earth, are driven towards the earth; that is to say, what is the cause of the descent of heavy bodies. Now if the action of the sun be hindered in the raising of vapours, and be not at all hindered in the casting of them down, the water will descend. But a cloud cannot hinder the action of the sun in making things of an earthly nature descend to the earth, though it may hinder it in making vapours ascend. For the lower part of a thick cloud is so covered by its upper part, as that it cannot receive that action of the sun by which vapours are carried up; because vapours are raised by the perpetual fermentation of the air, or by the separating of its smallest parts from one another, which is much weaker when a thick cloud is interposed, than when the sky is clear. And therefore, whensoever a cloud is made thick enough, the water, which would not descend before, will then descend, unless it be kept up by the agitation of the wind. Wherefore I have rendered a possible cause, both why the clouds may be sustained in the air, and also why they may fall down again to the earth; which was propounded to be done.

[Sidenote: How it could be that the moon was eclipsed, when she was not
diametrically opposite to the sun.]

16. Granting that the clouds may be frozen, it is no wonder if the moon have been seen eclipsed at such time as she hath been almost two degrees above the horizon, the sun at the same time appearing in the horizon; for such an eclipse was observed by Mæstlin, at Tubingen, in the year 1590. For it might happen that a frozen cloud was then interposed between the sun and the eye of the observer. And if it were so, the sun, which was then almost two degrees below the horizon, might appear to be in it, by reason of the passing of his beams through the ice. And it is to be noted that those, that attribute such refractions to the atmosphere, cannot attribute to it so great a refraction as this. Wherefore not the atmosphere, but either water in a continued body, or else ice, must be the cause of that refraction.

[Sidenote: By what means many suns may appear at once.]

17. Again, granting that there may be ice in the clouds, it will be no longer a wonder that many suns have sometimes appeared at once. For looking-glasses may be so placed, as by reflections to show the same object in many places. And may not so many frozen clouds serve for so many looking-glasses? And may they not be fitly disposed for that purpose? Besides, the number of appearances may be increased by refractions also; and therefore it would be a greater wonder to me, if such phenomena as these should never happen.

And were it not for that one phenomenon of the new star which was seen in Cassiopea, I should think comets were made in the same manner, namely, by vapours drawn not only from the earth but from the rest of the planets also, and congealed into one continued body. For I could very well from hence give a reason both of their hair, and of their motions. But seeing that star remained sixteen whole months in the same place amongst the fixed stars, I cannot believe the matter of it was ice. Wherefore I leave to others the disquisition of the cause of comets; concerning which nothing that hath hitherto been published, besides the bare histories of them, is worth considering.

[Sidenote: Of the heads of rivers.]

18. The heads of rivers may be deduced from rain-water, or from melted snows, very easily; but from other causes, very hardly, or not at all. For both rain-water and melted snows run down the descents of mountains; and if they descend only by the outward superficies, the showers or snows themselves may be accounted the springs or fountains; but if they enter the earth and descend within it, then, wheresoever they break out, there are their springs. And as these springs make small streams, so, many small streams running together make rivers. Now, there was never any spring found, but where the water which flowed to it, was either further, or at least as far from the centre of the earth, as the spring itself. And whereas it has been objected by a great philosopher, that in the top of Mount Cenis, which parts Savoy from Piedmont, there springs a river which runs down by Susa; it is not true. For there are above that river, for two miles length, very high hills on both sides, which are almost perpetually covered with snow; from which innumerable little streams running down do manifestly supply that river with water sufficient for its magnitude.

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CHAP. XXIX.

OF SOUND, ODOUR, SAVOUR, AND TOUCH.

1.. The definition of sound, and the distinctions of sounds.—2. The
cause of the degrees of sounds.—3. The difference between sounds
acute and grave.—4. The difference between clear and hoarse sounds,
whence.—5. The sound of thunder and of a gun, whence it proceeds.—6.
Whence it is that pipes, by blowing into them, have a clear
sound.—7. Of reflected sound.—8. From whence it is that sound is
uniform and lasting.—9. How sound may be helped and hindered by the
wind.—10. Not only air, but other bodies how hard soever they be,
convey sound.—11. The causes of grave and acute sounds, and of
concent.—12. Phenomena for smelling.—13. The first organ and the
generation of smelling.—14. How it is helped by heat and by
wind.—15. Why such bodies are least smelt, which have least
intermixture of air in them.—16. Why odorous things become more
odorous by being bruised.—17. The first organ of tasting; and why
some savours cause nauseousness.—18. The first organ of feeling; and
how we come to the knowledge of such objects as are common to the
touch and other senses.

[Sidenote: The definition of sound, and the distinction of sounds.]

1. SOUND _is sense generated by the action of the medium, when its motion reacheth the ear and the rest of the organs of sense_. Now, the motion of the medium is not the sound itself, but the cause of it. For the phantasm which is made in us, that is to say, the reaction of the organ, is properly that which we call _sound_.

The principal distinctions of sounds are these; first, that one sound is stronger, another weaker. Secondly, that one is more grave, another more acute. Thirdly, that one is clear, another hoarse. Fourthly, that one is primary, another derivative. Fifthly, that one is uniform, another not. Sixthly, that one is more durable, another less durable. Of all which distinctions the members may be subdistinguished into parts distinguishable almost infinitely. For the variety of sounds seems to be not much less than that of colours.

As vision, so hearing is generated by the motion of the medium, but not in the same manner. For sight is from pressure, that is, from an endeavour; in which there is no perceptible progression of any of the parts of the medium; but one part urging or thrusting on another propagateth that action successively to any distance whatsoever; whereas the motion of the medium, by which sound is made, is a stroke. For when we hear, the drum of the ear, which is the first organ of hearing, is stricken; and the drum being stricken, the _pia mater_ is also shaken, and with it the arteries which are inserted into it; by which the action being propagated to the heart itself, by the reaction of the heart a phantasm is made which we call sound; and because the reaction tendeth outwards, we think it is without.

[Sidenote: The cause of the degrees of sounds.]

2. And seeing the effects produced by motion are greater or less, not only when the velocity is greater or less, but also when the body hath greater or less magnitude though the velocity be the same; a sound may be greater or less both these ways. And because neither the greatest nor the least magnitude or velocity can be given, it may happen that either the motion may be of so small velocity, or the body itself of so small magnitude, as to produce no sound at all; or either of them may be so great, as to take away the faculty of sense by hurting the organ.

From hence may be deduced possible causes of the strength and weakness of sounds in the following phenomena.

The first whereof is this, that if a man speak through a trunk which hath one end applied to the mouth of the speaker, and the other to the ear of the hearer, the sound will come stronger than it would do through the open air. And the cause, not only the possible, but the certain and manifest cause is this, that the air which is moved by the first breath and carried forwards in the trunk, is not diffused as it would be in the open air, and is consequently brought to the ear almost with the same velocity with which it was first breathed out. Whereas, in the open air, the first motion diffuseth itself every way into circles, such as are made by the throwing of a stone into a standing water, where the velocity grows less and less as the undulation proceeds further and further from the beginning of its motion.

The second is this, that if the trunk be short, and the end which is applied to the mouth be wider than that which is applied to the ear, thus also the sound will be stronger than if it were made in the open air. And the cause is the same, namely, that by how much the wider end of the trunk is less distant from the beginning of the sound, by so much the less is the diffusion.

The third, that it is easier for one, that is within a chamber, to hear what is spoken without, than for him, that stands without, to hear what is spoken within. For the windows and other inlets of the moved air are as the wide end of the trunk. And for this reason some creatures seem to hear the better, because nature has bestowed upon them wide and capacious ears.

The fourth is this, that though he, which standeth upon the sea-shore, cannot hear the collision of the two nearest waves, yet nevertheless he hears the roaring of the whole sea. And the cause seems to be this, that though the several collisions move the organ, yet they are not severally great enough to cause sense; whereas nothing hinders but that all of them together may make sound.

[Sidenote: The difference between sounds acute and grave.]

3. That bodies when they are stricken do yield some a more grave, others a more acute sound, the cause may consist in the difference of the times in which the parts stricken and forced out of their places return to the same places again. For in some bodies, the restitution of the moved parts is quick, in others slow. And this also may be the cause, why the parts of the organ, which are moved by the medium, return to their rest again, sometimes sooner, sometimes later. Now, by how much the vibrations or the reciprocal motions of the parts are more frequent, by so much doth the whole sound made at the same time by one stroke consist of more, and consequently of smaller parts. For what is acute in sound, the same is subtle in matter; and both of them, namely acute sound and subtle matter, consist of very small parts, that of time, and this of the matter itself.

The third distinction of sounds cannot be conceived clearly enough by the names I have used of _clear_ and _hoarse_, nor by any other that I know; and therefore it is needful to explain them by examples. When I say hoarse, I understand whispering and hissing, and whatsoever is like to these, by what appellation soever it be expressed. And sounds of this kind seem to be made by the force of some strong wind, raking rather than striking such hard bodies as it falls upon. On the contrary, when I use the word clear, I do not understand such a sound as may be easily and distinctly heard; for so whispers would be clear; but such as is made by somewhat that is broken, and such as is clamour, tinkling, the sound of a trumpet, &c. and to express it significantly in one word, noise. And seeing no sound is made but by the concourse of two bodies at the least, by which concourse it is necessary that there be as well reaction as action, that is to say, one motion opposite to another; it follows that according as the proportion between those two opposite motions is diversified, so the sounds which are made will be different from one another. And whensoever the proportion between them is so great, as that the motion of one of the bodies be insensible if compared with the motion of the other, then the sound will not be of the same kind; as when the wind falls very obliquely upon a hard body, or when a hard body is carried swiftly through the air; for then there is made that sound which I call a hoarse sound, in Greek συριγμος. Therefore the breath blown with violence from the mouth makes a hissing, because in going out it rakes the superficies of the lips, whose reaction against the force of the breath is not sensible. And this is the cause why the winds have that hoarse sound. Also if two bodies, how hard soever, be rubbed together with no great pressure, they make a hoarse sound. And this hoarse sound, when it is made, as I have said, by the air raking the superficies of a hard body, seemeth to be nothing but the dividing of the air into innumerable and very small files. For the asperity of the superficies doth, by the eminences of its innumerable parts, divide or cut in pieces the air that slides upon it.

[Sidenote: The difference between clear & hoarse sounds, whence.]

4. _Noise_, or that which I call clear sound, is made two ways; one, by two hoarse sounds made by opposite motions; the other, by collision, or by the sudden pulling asunder of two bodies, whereby their small particles are put into commotion, or being already in commotion suddenly restore themselves again; which motion, making impression upon the medium, is propagated to the organ of hearing. And seeing there is in this collision or divulsion an endeavour in the particles of one body, opposite to the endeavour of the particles of the other body, there will also be made in the organ of hearing a like opposition of endeavours, that is to say, of motions; and consequently the sound arising from thence will be made by two opposite motions, that is to say, by two opposite hoarse sounds in one and the same part of the organ. For, as I have already said, a hoarse sound supposeth the sensible motion of but one of the bodies. And this opposition of motions in the organ is the cause why two bodies make a noise, when they are either suddenly stricken against one another, or suddenly broken asunder.

[Sidenote: The sound of thunder and of a gun, whence it proceeds.]

5. This being granted, and seeing withal that thunder is made by the vehement eruption of the air out of the cavities of congealed clouds, the cause of the great noise or clap may be the sudden breaking asunder of the ice. For in this action it is necessary that there be not only a great concussion of the small particles of the broken parts, but also that this concussion, by being communicated to the air, be carried to the organ of hearing, and make impression upon it. And then, from the first reaction of the organ proceeds that first and greatest sound, which is made by the collision of the parts whilst they restore themselves. And seeing there is in all concussion a reciprocation of motion forwards and backwards in the parts stricken; for opposite motions cannot extinguish one another in an instant, as I have shown in the 11th article of chapter VIII; it follows necessarily that the sound will both continue, and grow weaker and weaker, till at last the action of the reciprocating air grow so weak, as to be imperceptible. Wherefore a possible cause is given both of the first fierce noise of the thunder, and also of the murmur that follows it.

The cause of the great sound from a discharged piece of ordnance is like that of a clap of thunder. For the gunpowder being fired doth, in its endeavour to go out, attempt every way the sides of the metal in such manner, as that it enlargeth the circumference all along, and withal shorteneth the axis; so that whilst the piece of ordnance is in discharging, it is made both wider and shorter than it was before; and therefore also presently after it is discharged its wideness will be diminished, and its length increased again by the restitution of all the particles of the matter, of which it consisteth, to their former position. And this is done with such motions of the parts, as are not only very vehement, but also opposite to one another; which motions, being communicated to the air, make impression upon the organ, and by the reaction of the organ create a sound, which lasteth for some time; as I have already shown in this article.

I note by the way, as not belonging to this place, that the possible cause why a gun recoils when it is shot off, may be this; that being first swollen by the force of the fire, and afterwards restoring itself, from this restitution there proceeds an endeavour from all the sides towards the cavity; and consequently this endeavour is in those parts which are next the breech; which being not hollow, but solid, the effect of the restitution is by it hindered and diverted into the length; and by this means both the breech and the whole gun is thrust backwards; and the more forcibly by how much the force is greater, by which the part next the breech is restored to its former posture, that is to say, by how much the thinner is that part. The cause, therefore, why guns recoil, some more some less, is the difference of their thickness towards the breech; and the greater that thickness is, the less they recoil; and contrarily.

[Sidenote: Whence it is that pipes, by blowing into them, have a clear
sound.]

6. Also the cause why the sound of a pipe, which is made by blowing into it, is nevertheless clear, is the same with that of the sound which is made by collision. For if the breath, when it is blown into a pipe, do only rake its concave superficies, or fall upon it with a very sharp angle of incidence, the sound will not be clear, but hoarse. But if the angle be great enough, the percussion, which is made against one of the hollow sides, will be reverberated to the opposite side; and so successive repercussions will be made from side to side, till at last the whole concave superficies of the pipe be put into motion; which motion will be reciprocated, as it is in collision; and this reciprocation being propagated to the organ, from the reaction of the organ will arise a clear sound, such as is made by collision, or by breaking asunder of hard bodies.

In the same manner it is with the sound of a man's voice. For when the breath passeth out without interruption, and doth but lightly touch the cavities through which it is sent, the sound it maketh is a hoarse sound. But if in going out it strike strongly upon the _larynx_, then a clear sound is made, as in a pipe. And the same breath, as it comes in divers manners to the palate, the tongue, the lips, the teeth, and other organs of speech, so the sounds into which it is articulated become different from one another.

[Sidenote: Of reflected sound.]

7. I call that _primary sound_, which is generated by motion from the sounding body to the organ in a strait line without reflection; and I call that _reflected sound_, which is generated by one or more reflections, being the same with that we call _echo_, and is iterated as often as there are reflections made from the object to the ear. And these reflections are made by hills, walls, and other resisting bodies, so placed as that they make more or fewer reflections of the motion, according as they are themselves more or fewer in number; and they make them more or less frequently, according as they are more or less distant from one another. Now the cause of both these things is to be sought for in the situation of the reflecting bodies, as is usually done in sight. For the laws of reflection are the same in both, namely, that the angles of incidence and reflection be equal to one another. If, therefore, in a hollow elliptic body, whose inside is well polished, or in two right parabolical solids, which are joined together by one common base, there be placed a sounding body in one of the burning points, and the ear in the other, there will be heard a sound by many degrees greater than in the open air; and both this, and the burning of such combustible things, as being put in the same places are set on fire by the sun-beams, are effects of one and the same cause. But, as when the visible object is placed in one of the burning points, it is not distinctly seen in the other, because every part of the object being seen in every line, which is reflected from the concave superficies to the eye, makes a confusion in the sight; so neither is sound heard articulately and distinctly when it comes to the ear in all those reflected lines. And this may be the reason why in churches which have arched roofs, though they be neither elliptical nor parabolical, yet because their figure is not much different from these, the voice from the pulpit will not be heard so articulately as it would be, if there were no vaulting at all.

[Sidenote: From whence it is that sound is uniform and lasting.]