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Plutarch, Symposiacs
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When we supped with Ammonius at Athens, who was then the third time captain of the city-bands, there was a great noise about the house, some without doors calling, Captain! Captain! After he had sent his officers to quiet the tumult, and had dispersed the crowd, we began to inquire what was the reason that those that are within doors hear those that are without, but those that are without cannot hear those that are within as well. And Ammonius said, that Aristotle had given a reason for that already; for the sound of those within, being carried without into a large tract of air, grows weaker presently and is lost; but that which comes in from without is not subject to the like casualty, but is kept close, and is therefore more easy to be heard. But that seemed a more difficult question, Why sounds seem greater in the night than in the day, and yet altogether as clear. For my own part (continued he) I think Providence hath very wisely contrived that our hearing should be quickest when our sight can do us very little or no service; for the air of the "blind and solitary Night," as Empedocles calls it, being dark, supplies in the ears that defect of sense which it makes in the eyes. But since of natural effects we should endeavor to find the causes, and to discover what are the material and mechanical principles of things is the proper task of a natural philosopher, who shall first give us a rational account hereof?
Boethus began, and said: When I was a novice in letters, I then made use of geometrical postulates, and assumed as undoubted truths some undemonstrated suppositions; and now I shall make use of some propositions which Epicurus hath demonstrated already. Bodies move in a vacuum, and there are a great many spaces interspersed among the atoms of the air. Now when the air being rarefied is more extended, so as to fill the vacant space, there are only a few vacuities scattered and interspersed among the particles of matter; but when the atoms of air are condensed and laid close together, they leave a vast empty space, convenient and sufficient for other bodies to pass through. Now the coldness of the night makes such a constipation. Heat opens and separates parts of condensed bodies, and therefore bodies that boil, grow soft, or melt, require a greater space than before; but, on the contrary, the parts of the body that are condensed or freeze are contracted closer to one another, and leave those vessels and places from which they retired partly empty. Now the sound, meeting and striking against a great many bodies in its way, is either altogether lost or scattered, and very much and very frequently hindered in its passage; but when it hath a plain and smooth way through an empty space, and comes to the ear uninterrupted, the passage is so sudden, that it preserves its articulate distinctness, as well as the words it carries. You may observe that empty vessels, when knocked, answer presently, send out a noise to a great distance, and oftentimes the sound whirled round in the hollow breaks out with a considerable force; whilst a vessel that is filled either with a liquid or a solid body will not answer to a stroke, because the sound hath no room or passage to come through. And among solid bodies themselves, gold and stone, because they want pores, can hardly be made to sound; and when a noise is made by a stroke upon them, it is very flat, and presently lost. But brass is sounding, it being a porous, rare, and light metal, not consisting of parts tightly compacted, but being mixed with a yielding and uncompacted substance, which gives free passage to other motions, and kindly receiving the sound sends it forward; till some touching the instrument do, as it were, seize on it in the way, and stop the hollow; for then, by reason of the hindering force, it stops and goes no further. And this, in my opinion, is the reason why the night is more sonorous, and the day less; since in the day, the heat rarefying the air makes the empty spaces between the particles to be very little. But, pray, let none argue against the suppositions I assumed.
And I (Ammonius bidding me oppose him) said: Sir, your suppositions which demand a vacuum to be granted I shall admit; but you err in supposing that a vacuum is conducive either to the preservation or conveyance of sound. For that which cannot be touched, acted upon, or struck is peculiarly favorable to silence. But sound is a stroke of a sounding body; and a sounding body is that which has homogeneousness and uniformity, and is easy to be moved, light, smooth, and, by reason of its tenseness and continuity, it is obedient to the stroke; and such is the air. Water, earth, and fire are of themselves soundless; but each of them makes a noise when air falls upon or gets into it. And brass hath no vacuum; but being mixed with a smooth and gentle air it answers to a stroke, and is sounding. If the eye may be judge, iron must be reckoned to have a great many vacuities, and to be porous like a honey-comb, yet it is the dullest, and sounds worse than any other metal.
Therefore there is no need to trouble the night to contract and condense its air, that in other parts we may leave vacuities and wide spaces; as if the air would hinder and corrupt the substance of the sounds, whose very substance, form, and power itself is. Besides, if your reason held, misty and extreme cold nights would be more sonorous than those which are temperate and clear, because then the atoms in our atmosphere are constipated, and the spaces which they left remain empty; and, what is more obvious, a cold day should be more sonorous than a warm summer's night; neither of which is true. Therefore, laying aside that explication, I produce Anaxagoras, who teacheth that the sun makes a tremulous motion in the air, as is evident from those little motes which are seen tossed up and down and flying in the sunbeams. These (says he), being in the day-time whisked about by the heat, and making a humming noise, lessen or drown other sounds; but at night their motion, and consequently their noise, ceaseth.
When I had thus said, Ammonius began: Perhaps it will look like a ridiculous attempt in us, to endeavor to confute Democritus and correct Anaxagoras. Yet we must not allow that humming noise to Anaxagoras's little motes, for it is neither probable nor necessary. But their tremulous and whirling motion in the sunbeams is oftentimes sufficient to disturb and break a sound. For the air (as hath been already said), being itself the body and substance of sound, if it be quiet and undisturbed, makes a straight, easy, and continuous way to the particles or the motions which make the sound. Thus sounds are best heard in calm still weather; and the contrary is seen in stormy weather, as Simonides hath it:-
No tearing tempests rattled through the skies, Which hinder sweet discourse from mortal ears.
For often the disturbed air hinders the articulateness of a discourse from coming to the ears, though it may convey something of the loudness and length of it. Now the night, simply considered in itself, hath nothing that may disturb the air; though the day hath - namely the sun, according to the opinion of Anaxagoras.
To this Thrasyllus, Ammonius's son, subjoining said: What is the matter, for God's sake, that we endeavor to solve this difficulty by the unintelligible fancied motion of the air, and neglect the tossing and divulsion thereof, which are evident? For Jupiter, the great ruler above, doth not covertly and silently move the little particles of air; but as soon as he appears, he stirs up and moves everything.
He sends forth lucky signs, And stirs up nations to their proper work,
And they obey; and (as Democritus saith) with fresh thoughts for each new day, as if newly born again, they fall to their worldly concerns with noisy and effectual contrivances. And upon this account, Ibycus oppositely calls the dawning [Greek omitted] (from [Greek omitted], TO HEAR), because then men first begin to hear and speak. Now at night, all things being at rest, the air being quiet and undisturbed must therefore probably transmit the voice better, and convey it whole and unbroken to our ears.
Aristodemus the Cyprian, being then in the company, said: But consider, sir, whether battles or the marches of great armies by night do not confute your reason; for the noise they make seems as loud as otherwise, though then the air is broken and very much disturbed. But the reason is partly in ourselves; for our voice at night is usually vehement, we either commanding others to do something or asking short questions with heat and concern. For that, at the same time when Nature requires rest, we should stir to do or speak anything, there must be some great and urgent necessity for it; and thence our voices become more vehement and loud.