Another collection of philosophical conferences of the French virtuosi upon questions of all sorts for the improving of natural knowledg made in the assembly of the Beaux Esprits at Paris by the most ingenious persons of that nation / render'd into English by G. Havers, Gent. & J. Davies ..., Gent.

CONFERENCE CXIII. I. Of the Iris, or Rain-bow. II. Whether the Reading of Books is a fitter way for Learning than Vocal Instructions? (Book 113)

'TWas not without reason that the Poets feign'd Iris to be [ I] the Daughter of Thaumas, or Thaumasia; that is to say,* 1.1 of Admiration: thereby intimating our not knowing its cause: For Wonder is the Off-spring of Ignorance. Amongst many other things, Three we find to admire in it; its Matter, Form, and Colours. Its Matter is not a moist Cloud, as most imagine; for (besides that then we should see Rain-bows more frequently than we do) a Cloud cannot reflect the Sun-beams with that va∣riety or medley which we observe therein: For there would be but one colour, if the Cloud were diaphanous; and otherwise, it will be black and dark. 'Tis not therefore in a Cloud that the Rain-bow is form'd, but in the falling drops of Rain; as we see some Fountains form one in the Air, by the ejaculation of the Water struck with the Sun-beams; as also by the spurt∣ing of Water out of the mouth, opposite to the Sun: For an Iris is not visible, unless we be plac'd between the dropping Cloud and the Sun. If the Cloud be between our eye and the Sun, it will receive the Rays only on that side which is next the Sun, and not on that side which is towards us. Nor will any Iris appear, in case the Sun be between the Eye and the Cloud: For, accord∣ing to the common opinion, it cannot be seen higher than three miles; but in this opposition of the Sun, the Iris will be remote from us above 18 degrees, which make above 1100 miles, al∣lowing 60 miles to a degree, according to Ptolomie. Hence the Rain-bow which appears before Noon, is always towards the West; as that which appears about or after Noon, is always to∣wards the North, or the East; at which times we are between the Rain-bow, and the Sun. Hence such as are in the fifth Cli∣mate can never see one in the South. Now the surfaces of these

drops of Water (which fall confusedly and disorderly) being irregular, and struck obliquely by the Sun-beams, they make a refraction of his Light, like that which is made by Diamonds cut into Faucets, but more permanent; because the drops of Water fall so swiftly and successively that they seem continuous. A Rain-bow then is nothing else but the Light of the Sun, re∣ceiv'd in this falling Rain, and remitted to our eye by an Angle of refraction, different from that of its incidence; for if it were equal, the Image of the Sun would appear therein too, as we see it doth in Parhelia's. Indeed we may say, That the Rain-bow is an imperfect and begun Parhelion; the Light of the one being reflected regularly, and that of the other in confusion, and disorderly: And, That its Arch and circular Figure proceeds from the obliquity of the Sun-beams: Or else, That he being a Spherical Body, casts his Rays circularly: Or, lastly, from the Spherical or Parabolical form of the Cloud: Which is also true in the Iris which is form'd in the night by the Moon-beams, re∣ceiv'd in a Cloud dissolving into Rain; saving that her Rays, being not so strong and luminous as those of the Sun, illuminate only the surface of the Water, and therein paint a faint whitish colour, and not such an enamel of colours as is seen by day in the Solar Iris; which colours are nothing else but an imperfect Light, which cannot be directly reflected to the eye, by reason of the inequality of the Angles, and therefore at least forms these Colours; of which the three principal are, Yellow, or Ci∣trinous, which is the highest; Blue, or Green, which is the middlemost; and Red, which is the lowest: Amongst which there are found divers others which partake of their extremi∣ties; the diversity whereof proceeds from the divers reception of the Rays in the Parts of the Cloud, differing in opacity; which not being great in the outmost part, the Sun-beams paint there a Yellowish colour; but greater in the middle, a Blew or Watchet; and greatest in the inmost or lowest part, a Red: as Experience shews us in the like subjects, wherein Light diversly modifi'd, represents very neer the same variety of Colours; which although not real (as those which arise from the various mixture of the four Elementary Qualities) yet are not absolutely imaginary (as those are which are seen by weak eyes about the flame of a Candle), but are true Colours, inasmuch as they strike the Sight, which a sensitive and corporeal Power, and are alike perceiv'd by all; nevertheless, they are less material than Elementary Colours, and are neerer akin to Light, not differ∣ing from the same, saving inasmuch as it is here received diversly in the eye, according to the rarity or density, situation, figure, and other qualities of the Object and Medium.

The Second said, The Rain-bow (the fairest not only of all Meteors, but of all Nature's Works; being, according to the Cabbalists, the Throne of God, who, in the Apocalypse, is repre∣sented Crown'd therewith) doth not less dazle the Mind than

ravish the Eye; it being observ'd, That the clearer things are to the Sense the obscurer they are to the Understanding; and so on the contrary: For it cannot proceed from the different rarity and density of the Cloud, which being never alike, but infinite∣ly various, should rather represent a thousand different Figures and Colours; whereas the Rain-bow hath always a circular Fi∣gure, and the same Colours. And as there may be found more Clouds in several places, equally rare or dense, and equally di∣stant from the Sun (who enlightens Bodies equally distant after the same manner) so there should be more Rain-bows at the same time in several places; which is contrary to experience: For we never see two uniform Rain-bows at once; the other Bow, some∣times included in the first, being not directly form'd by the Sun-beams, but by reflection of the Rays of the first Bow upon a neigh∣bouring Cloud; whence the Colours of such secondary-Bow are not so lively as those of the first, but are revers'd, the yellow being lowest, the Green always middlemost, and the Red uppermost: For so by the reason of Catoptricks, we see that the Species re∣flected have a different situation from the Body which produces them (things on the right hand appearing on the left, and con∣trarily); and the shadows of Bodies which pass along the street entring by a small hole into a dark Chamber, revers'd.

The Third said, Experience teaches us, That when Light passes out of a thinner Medium into a thicker (as out of Air into Water) if it fall obliquely upon that thicker Medium, it is bro∣ken or refracted: But if it pass quite through such denser Medi∣um, so that 'tis broken as well at its going out as at its entrance (especially if the refraction in these two places be great enough) then this Light is turn'd into Colours. This Natural Effect is a Principle of the Opticks, and is observ'd not only in the Rain-bow, but also in triangular Crystals, and Glasses fill'd with clear Water, and expos'd to the Sun; provided the Glass be of a co∣nical Figure revers'd; that is, narrower at the bottome, and wider towards the top. This being premis'd, the Production of the Rain-bow seems to be thus: When a Cloud, already wholly turn'd into Water, and actually falling down in drops of Rain (which reach from the top of the Cloud to the Earth) is shin'd upon by the opposite Sun, and the Spectator is plac'd be∣tween the Sun and the Rain, then the Sun-beams passing through those drops, are reflected, as by a Mirror, back again, by those which are more remote; and passing by the sides of those which are nearest (because from one and the same part but one perpen∣dicular Ray can fall upon a round Figure, as that of drops of Water is, all the other Rays being oblique) they must of neces∣sity be twice broken: First, as they are reflected by the remoter drops, and pass out of the Air comprehended between those remoter, into the other drops nearer us: And secondly, as they issue out of these nearer drops, into the Air which is between them and us. And thus from this different fraction caus'd by the

various rarity and density of the Air and Water, the diversity of Colours in the Rain-bow ariseth. For, Water being not altoge∣ther diaphanous, but somewhat of a middle nature, between perfectly Transparent and Opake, reflects part of the Rays which fall upon its surface, and lets the other part pass through; as 'tis observ'd in Rivers and Ponds, upon which we see the Suns Image by reflection, but Divers and Fish behold it by refraction. So 'tis with drops of Water; those neerest us reflect part of the Sun-beams towards the Sun himself, without forming an Iris, because these reflected Rays meet not other drops to refract them; but when part of those Rays, which pass'd through the small intervals of the first drops, are reflected by the other remo∣ter from us, then these reflected Rays lighting by the way upon the first drops between which they had pass'd, they are broken thereby both at their going in and coming out, where they re∣present the Iris, which consequently is form'd by Reflection and Refraction; reflection, by all the drops which receive Light, re∣mitting the same towards the Sun; and refraction of the same Light so reflected, when by the way as it returns it meets those other drops of Water, which refract it twice, and give it the diversity of Colours, which ariseth from the divers reception of the Light into those parts of Water, more or less dense and rare. But now to give account of the circular Figure of this Meteor, which is not only in appearance circular (as square Towers seem round at a distance) but is so really; 'tis requisite to take a cer∣tain position of the Sun; and by one example 'twill be easie to judg of others. Let us suppose then that the Sun is at the Hori∣zon, and consequently that all the Rays he sends directly upon the drops of Rain, as well the highest as the lowest, are parallel between themselves, and to the Horizon, (for the elevation of a Cloud, how great soever, being inconsiderable in respect of the Sun's distance from the Earth, hinders not but that all his Rays are always parallel between themselves) which being reflected, as hath been said, the reflection of them will be also parallel to the Horizon, or very neer so; for here we consider only that which is made by the middle of the drop, which is the strongest by reason of its round figure; and this reflection being receiv'd by the superior part of some other drop which it finds in its way, and there twice broken, to wit, at its going in and com∣ing forth; the two Refractions joyn'd together distort the Ray about 45 degrees; that is to say, the Ray thus twice broken will make with the lines parallel to the Horizon an Angle of 45. degrees, a 〈…〉〈…〉 from on high downwards, and falling up∣on the Earth. And because all the drops make such a Refrac∣tion as we have mention'd, therefore all such Persons as shall be between the Sun and the drops of Rain, shall see the Iris of the same heighth, namely, of 45 degrees (although from several stations); some in the lower drops, namely, such Persons as are neerest the Cloud; others, to wit, such as are more remote,

in the higher drops; because they all see it by Rays parallel be∣tween themselves, and consequently by equal Angles. Now the drops make refraction not only by their superior parts, but also by their sides and lower parts; whence those on either side of the Spectator, distant by an Angle of 45 degrees, will make him see their refraction, and consequently the Iris on either side under equal Angles; which being made on all sides about a right line drawn from the Sun to the Spectators eye, which may be call'd the Axis of the Iris, it necessarily follows, That the Iris must appear perfectly round about this Axis: So that the drops elevated above this Axis 45 degrees, will make the upper part of the Iris by the refraction of their superior parts. Those on either side, distant likewise 45 degrees, will make the sides of the Iris by refraction of their parts which are at the remoter sides; and so of all the drops which shall be about the Axis, under equal Angles of 45 degrees. As for other drops neerer or further from the Axis and the Spectator, they will represent an Iris to others who are not in the same Axis, but neerer or re∣moter from the Cloud, and situate in such place that those drops appear distant from the Axis by Angles of 45 degrees. So that as many Spectators as there are between the Sun and the Cloud, and not in the same Axis; so many Axes must be imagin'd, about which there are different Arches and Rainbows. Now in this Horizontal Position the Bow appears a perfect Semi-circle, whose Center is in the Horizon, at the Point where the Axis termi∣nates. But when the Sun is in another Position, as elevated some degrees yet fewer than 45, then the Axis of the Iris com∣ing from the Sun through the Spectator's eye, penetrates the Earth; and so the Center (which is always at the end of the Ax∣is) is below the Horizon; and the portion of the Iris which we behold is less than a Semi-circle, greater than which it never ap∣pears, as Aristotle hath well observ'd. For since the Bow is al∣ways less than a Semi-circle whilst the Sun is elevated above the Horizon, it must be a Semi-circle when he is in the Horizon, and none at all when he is below the Horizon, because he doth not then illuminate the Cloud: Hence 'tis seldome produc'd in Win∣ter, because when it rains in that Season the whole Heaven is cloudy, and covers the Sun-beams; as neither in the Summer and Spring at noon, when the Sun is higher than 45 degrees, but only at Morning and Evening.

The Fourth said, That if Aristotle's definition of the Rain∣bow be true, who defines it, An Arch consisting of divers colours, which the reflection of the Sun-beams represents upon a hollow Cloud ready to dissolve into Rain, we need not seek much for Material, Formal, and Efficient Causes (for he assigns no Final of it; but the Scripture doth, namely, to be a moral sign of the Covenant between God and Men.) Of the first there is no doubt, unless amongst blind men, to whom only God can make a demonstration of it; but the rest are very obscure: To judg

of which we must observe, That the Angle of Reflection is equal to that of Incidence; so that a right perpendicular Line, erected at the common point of Incidence and Reflection, will equally bisect the Angle comprehended by the Ray of Incidence and that of Reflection; which is not true, unless when the Ray of Incidence is terminated by a very smooth and opake Body, as that of a Mirror: Whence 'tis infer'd, That a Cloud not having such evenness or smoothness will not reflect the Light or Ray at an equal Angle, but will dissipate and remit it elsewhere: So that if one part of a Cloud, which is directly opposite to the Sun and smooth, reflect the Ray directly; and another obliquely opposite to him, dis••ort and reflect it elsewhere (as 'tis much more probable, than always to imagine Clouds exactly smooth, polish'd, and even) it appears, That there will not be form'd a Figure of an Arch uniformly colour'd, but rather a confus'd medley of colours. Besides, if Reflection represent any thing, 'tis the same thing that is opposite, not another: But 'tis not the Sun that we behold in the Cloud, but a mixture of Colours, no wise like, nor so much as an imperfect representation of him, as some have pleased to affirm: For Reflection would shew us either the Sun, or an imperfect representation of him; not in the Cloud, but as far beyond it as the Object (the Sun) is from it. So that we shall explicate Aristotle better if we say, That those Colours appear by irradiation; and, that the Light diversly receiv'd, and not reflected, makes the variety of this goodly Spectacle: For they who say 'tis Refraction, are mistaken; for Refraction only alters the place of the Object represented by the Species, which is broken by the occurse of a Medium of unequal opacity; but doth not produce divers colours, such as those of the Iris, which I conceive we may more safely admire, with many other of God's Works (indisputable testimonies of his Power and our Weakness) than vainly seek their Causes.

The Fifth said, He conceiv'd no demonstration more manifest to prove the manner of the Rain-bows production than the ex∣periment of a Phial of Water, which, expos'd to the Sun upon some solid Body, represents the same Colours with those of the Rain-bow: So that the same thing is done in the Sky when the Sun-beams pass cross an aqueous and diaphanous Cloud, and are reflected to the other side by another Cloud, whose thickness hath some resemblance of solidity; and so 'tis not sufficient that such aqueous Cloud be interpos'd between the Sun and the Eye, but there must be also another opposite Cloud, dense enough to reflect those Rays of the Sun, who being hollow according to the figure of the Sky, imprints that lucid circular Figure, and gives it the name of a Bow.

The Sixth said, That a Rain-bow may be foretold some time before it happens, when the Wind comes from that Quarter where the Sun is, and a Cloud coming from the same Quarter pass over our heads, and shed Rain as it passes: For if the Sun

appears at the same time, you will see an Iris as soon as the Cloud becomes opposite to him; which Iris will be the more lively and colour'd, according as the falling Rain was greater, and the Sun happens to be clear; as also so much more elevated as the Sun is depress'd. But if the Sun be 45 degrees high, you will see no Iris, the Refraction not being then proper to produce it. If it happens after Rain, it signifies fair weather, and the Sky clears up, in that Quarter whence the Wind blows. But if the Wind blow from the Quarter opposite to the Sun, and drive a Cloud and Rain before it; and if the Sun also appear at the same time, then you will see the Iris before the Rain, which we may foretel will fall upon the place whence the Iris is beheld, provided the Cloud can subsist any while, and be not too speedily resolv'd all into Rain at the place where it is seen; for where ever an Iris is seen, there it rains.

Upon the Second Point it was said, That the Eye and the Ear [ II] being the Senses whereby the Mind receives the Species of things which it knows; the former is proper for Invention;* 1.2 and the latter, call'd the Sense of Discipline, chiefly for Learning. For the Voice, as the Proverb saith, is more powerful than dumb Masters; because being animated with the gesture and motion of the Eyes, Mouth, Hands, and whole Body, it makes more impression upon the Mind than the dead style of Books; which besides, being Instructors whom we cannot interrogate concern∣ing our doubts, as we may the living, they leave more scruples in the Readers mind than they resolve: For our cognition de∣pending on the Species and Animal Spirits, these follow the drift and motion of the Voice, whose accents consequently being joy∣ful, sad, amorous, warlike, or furious, according to the vari∣ety of the subject, imprint like affections in the Soul; and this through the near communication there is between the Air and those Spirits of the Body, which are also aerious, and of great mobility. And since Writing is only the sign of Speech, as this is of the Minds conception, it less perfectly expresses its Author's thought than the Voice, the perfect Image of his Conception, which is call'd the Internal Speech, as the voice is the External; and being the Original from which Writing is drawn, represents our Conceptions better than the Copy; as all Exemplars dege∣nerat proportionably to their remoteness from their Prototype.

The Second said, That written Discourses are better digested, and sustain themselves better by their own weight, than words disguis'd by the maner of expression, or cadence, gestures, and other sleights, which corrupt the simplicity of things; whence the Comedian that comforted Demosthenes, and reviv'd his lost desire of haranguing, made him confess, That one and the same verse of Homer was another thing when well and when ill pro∣nounc'd: And bad Poets fear nothing so much as that others should read their Works; the Name which themselves give them

causing others to judg them different from what they are; and the suddenness of pronuntiation not allowing the mind suffici∣ent time to reflect upon them. Moreover, Books flatter much less, and have more universal Precepts than Speech, which com∣monly affects complaisance, and the gaining of the hearers good will: Particularly in morality, Great Persons are better instru∣cted and more plainly reprehended for their faults by Books than by Discourses, which seldom tell them the truth freely, every one fearing the effects of hatred ensuing it, which Books care not for. Besides, No discipline is harder than Politicks; which being the Mistress of all others, may justly give Law to them. And were the way of learning the Sciences by Books longer than that by the Voice, yet 'tis the safer, yea, almost that alone by which we reap benefit; all those that are Learned, having learn'd more by the Reading and Meditation of Books, than by having heard the Voice of their Masters in Schools, where often∣times the noise is greater than the fruit. For, our Memories be∣ing treacherous, we never repeat things so well as we write them; and in case of mistakes or omissions, we are asham'd to acknowledg our faults, but defend them with obstinacy; whereas we scruple not to correct a Writing, to view and review it, and, according to Horace's counsel, keep it nine years before publishing. But Words are utter'd as soon as thought; and hence when we see those fine Discourses in Writing, which ra∣vish'd all the World in the Chair and at the Bar, we are often∣times asham'd of having admir'd them: Which perhaps as much or more kept Cicero from letting his Orations be read in his youth, as his pretended excuse of reserving to himself the liber∣ty of contradicting himself. Wherefore there being more to be learn'd in a well-digested and exact Piece, Writing (which is or∣dinarily such) must also be more proper for Instruction: Which is so true in the Mathematicks, to which alone the name of Dis∣cipline belongs, that none ever presum'd either to teach or learn them by Speech alone.

The Third said, That a good Comparison must be of things alike; and so if we compare Speech and Writing, it must be in respect of two things equally perfect in their kind; as an exact Discourse, and an exact Writing. You must also bring two ca∣pacities of the same pitch, and they must have equal time to learn the same thing; in which case, the circumstances being the same, there's no doubt but Speech is more advantageous there∣unto than Writing, which is not absolutely necessary, as the Voice is, without which the latter is unserviceable; he who reads be∣ing unable to understand any thing, unless he hath already heard it spoken of. Hence one naturally deaf is uncapable not only of the Sciences, but also of the use of Reason, yea, of Speech too: Whereas, on the contrary, some born blind, and who conse∣quently never read, have nevertheless prov'd very learned. And this prae-eminence of Speech above Writing, appears espe∣cially

in that the latter cannot be expressed without the former. Whence some justly doubt whether dead Languages, even such as are most familiar to us, as Greek and Latine, are not lost as to their best part, their pronunciation: So that the Greeks and La∣tines of Demosthenes and Cicero's time, would possibly no more understand us speaking Greek and Latine, than those of the present Age: Whence 'twould not be knowing of things, to know them only by Books, by which also none ever learn'd Languages, but only by Speech.

The Fourth said, That this Question admits not of an abso∣lute determination, in regard of the different capacities of Tea∣chers and Learners, as also of the Arts or Disciplines which are learn'd: For nimble Heads, and impatient of Labour, such as the Cholerick and Sanguine commonly are, suit better with Vocal Instructions than with Reading; which, on the contrary is more pleasing and profitable to the Melancholy and Phlegma∣tick, who take more time for reflection and meditation upon what they read. Again, Such Disciplines as consist chiefly in Contemplation, as Divinity, Natural Philosophy; the pure Mathematicks; together with those which require great Memo∣ry, as History and Law, have more need of Reading. But those that consist in Action are better learn'd by Speech, which hath more affinity with action, and sets it out better; Such is Oratory, the practical part of Physick and Law, Mechanick Arts, and Handicrafts, which 'tis impossible to learn by Books, although one may be render'd more perfect therein by them.

Notes

• * 1.1

  Of the Rain-bow.
• * 1.2

  Whether the Reading of Books is a fit∣ter way for Learning than Vocal Instruction?