Donor challenge: Your generous donation will be matched 2-to-1 right now. Your $5 becomes $15! Dear Internet Archive Supporter,. I ask only once a year. The Treatise on Light of Huygens has, however, withstood the test of time: and even now the exquisite skill with which he applied his. Treatise on Light In which are explained the causes of that which occurs in Christiaan Huygens. translated by Silvanus P. Thompson.

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Treatise on Light / Christiaan Huygens

It appears from the things explained above that the progression or propagation of a small part of a wave of light is properly what one calls a ray. And then, marking on the surface of the Crystal the point H where the intersection E llght, this point will be directly above E.

Now in the same time the piece A would have come to G along the straight line AG, equal and parallel to CB; and all the portion of wave AC would be at GB if the matter of the transparent pn transmitted the movement of the wave as liight as the matter of the Ether. Let a piece be covered with water for a day or more, the surface loses its natural polish. I shall therefore essay in this book, to give, in accordance with the principles accepted in the Philosophy of the present day, some clearer and more probable reasons, firstly of these properties of light propagated rectilinearly; secondly of light which is reflected on meeting other bodies.

To which the reply is easy if one remembers what has been said before. And thus the incident ray DA does not lighy pierce the surface AB. But we must consider still more particularly the origin of these waves, and the manner in which they spread. The effects of which refractions are very remarkable; for by them we often see objects which the rotundity of the Earth ought otherwise to hide; such as Islands, and the tops of mountains when in is at sea.

But, for the present, without yet deciding one or other, we will consider these spheroids only in those sections of them which make ellipses in the plane of this figure. But on the contrary one finds that the sphere resists the impress of movement only in proportion to the quantity of matter of the glass of which it is made. For the surface consisting thus tfeatise particles put together, and the ethereal particles being above, and smaller, it is evident that one could not demonstrate the equality of the angles of incidence and reflexion by similitude to that which happens to a ball thrown against a wall, of which writers have always made use.

Christiaan Huygens Treatise on Light was published in and is probably the largest scientific volume on light published before Newton’s Opticks. It was after having explained the refraction of ordinary transparent bodies by means of the spherical emanations of light, as above, that I resumed my examination of the nature of this Crystal, wherein I had previously been unable to discover anything.

Treatise on Light (Illustrated Edition)

But the truth is that this matter not only passes through solids, but does so even with great facility; of which the experiment of Torricelli, above cited, is already a proof. However, one will see hereafter that we have to suppose such an equality not so much as a necessity for the propagation of light as for rendering that propagation easier and more powerful; for it is not beyond the limits of probability that the particles of the ether have been made equal for a purpose so important as that of light, at least in that vast space which is beyond the region of atmosphere and which seems to serve only to transmit the light of the Sun and the Stars.


Now, however small we make the opening BG, there is always the same reason causing the light there to pass between straight lines; since this opening is always large enough to contain a great number of particles of the ethereal matter, which are of an inconceivable smallness; so that it appears that each little portion of the wave necessarily advances following the straight line which comes from the luminous point.

Then draw back the eye towards O, keeping always in the plane perpendicular through AB, so that the image of the line CD, which is formed by ordinary refraction, may appear in a straight line with the line KL viewed without refraction; and then mark on the Crystal the point N where the point of intersection E appears.

But it is still certain that this progression of motion is not instantaneous, but successive, and therefore must take time. Now it appears that AK and BL dip down toward the side where the air is less easy to penetrate: There will be seen in it demonstrations of those kinds which do not produce as great a certitude as those of Geometry, and which even differ much therefrom, since whereas the Geometers prove their Propositions by fixed and incontestable Principles, here the Principles are verified by the conclusions to be drawn from them; the nature of these things not allowing of this being done otherwise.

Whence it is to be remarked that though the movement of the ethereal matter might communicate itself partly to that of the reflecting body, this could in nothing alter the velocity of progression of the waves, on which the angle of reflexion depends.

Refresh and try again. We know that by means of the air, which is an invisible and impalpable body, Sound spreads around the spot where it trewtise been produced, by a movement which is passed on successively from one part of the air to another; and that the spreading of this movement, taking place equally rapidly on all sides, ought to form spherical surfaces ever enlarging and which strike our ears.

And so, by our hypothesis, we explain perfectly the phenomenon mentioned above; to wit, that when there are two huyvens equally inclined, but coming from opposite sides, as here the rays RC, rctheir refractions diverge equally from chrietiaan line followed by the refraction of the ray perpendicular to the surface, by considering these divergences in the direction parallel to the surface of the crystal. In it he speculated on the existence of extraterrestrial life, on other planets, which he imagined was similar to that on Earth.

What I find to be most probable herein, is to say that metallic bodies, which are almost the only really opaque ones, have mixed amongst their hard particles some soft ones; so that some serve to cause reflexion and the others to hinder transparency; while, on the other hand, transparent bodies contain only hard particles which have the faculty of recoil, and serve together with those of the ethereal matter for the propagation of the waves of light, as has been said.

Eric Byrnes rated it really liked it Jun 04, Want to Read saving…. And one must imagine the same about every point of the surface and of chrishiaan part within the flame. Lighht it apparently occurs against the particles of the air or others mingled with the ethereal particles and larger than they.


Lewis Kreger rated it liked it Aug 05, Return to Book Page. And even that one which was used to strike remains motionless with them.

Treatise on Light by Christiaan Huygens – Free at Loyal Books

Furthermore these refractions are not altogether constant in all weathers, particularly at small elevations of 2 or 3 degrees; which results from the different quantity of aqueous vapours rising above the Chrixtiaan.

And hence one sees the reason why light, at least if its rays are not reflected or broken, spreads only by straight lines, so that it illuminates no object except when the path from its source to that object is open along such lines.

That is to say that if the tretaise AB in entering the transparent body is refracted into BC, then likewise CB trreatise taken as a ray in the interior of this body will be refracted, on passing out, into BA. When I say plane, that does not signify a perfect evenness, but such as has been understood in treating of reflexion, and for the same reason.

And none can read his investigation of the phenomena found in Iceland spar without marvelling at his insight and sagacity. Now it is to be remarked that from the moment when the angle DAQ is smaller than is requisite to permit the refracted ray DA to pass into the other transparent substance, one finds that the interior reflexion which occurs at the surface AB is much augmented in brightness, as is easy to realize by experiment with a triangular prism; and for this our theory can afford this reason.

The axes or rather the major diameters of these I supposed to be oblique to the plane AB, as is AV the semi-axis or semi-major diameter of the spheroid SVT, which represents the partial wave coming from the point A, after the wave RC has reached AB. For an iron spike effects an entrance into it as easily as into any other Talc or Alabaster, to which it is equal in gravity.

If one considers further the other pieces H of the wave AC, it appears that they will not only have reached the surface AB by straight lines HK parallel to CB, but that in addition they will have generated in the transparent air, from the centres K, K, K, particular spherical waves, represented here by circumferences the semi-diameters of which are equal to KM, that is to say to the continuations of HK as far as the line BG parallel to AC.

And this is easy to conceive as regards water and other transparent liquids, they being composed of detached particles. The rarity of transparent bodies being then such as we have said, one easily conceives that the waves might be carried on in the ethereal matter which fills the interstices of the particles. Christiaan Huygens was born on 14 April in The Hague, into a rich and influential Dutch family, the second son of Constantijn Huygens.

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