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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Let A be the Sun, BCDE the annual lighr of the Earth, F Jupiter, GN the orbit of the nearest of his Satellites, for it is this one which is more apt for this investigation than any of the other three, because of the quickness of its revolution. But what may at first appear full strange and even incredible is that the undulations treatiee by such small movements and corpuscles, should spread to such immense distances; as for example from the Sun or from kight Stars to us. Let us also suppose that it is perpendicular to the Horizon, the portion B being nearer to the Earth than the portion A; and that because the vapours are less hindering at A than at B, the particular wave which comes tgeatise the point A spreads through a certain space AD while the particular wave which starts from the point B spreads through a shorter space BE; AD and BE being parallel to the Horizon.

Again, if one turns the Crystal in such wise that an incident ray Cyristiaan, of sunlight, which I suppose to be in the plane continued from GCFH, makes with GC an angle of 73 degrees and 20 minutes, and is consequently nearly parallel to the edge Hyygens, which makes with FH an angle of 70 degrees 57 minutes, according to the calculation which I shall put at the end, it will divide itself at the point O into two rays, one of which will continue along OP in a straight line with NO, and will similarly pass out of the other side of the crystal without any refraction; but the other will be refracted and will go along OQ.

One sees also the reason for a noteworthy accident which happens in this refraction: So on the other hand the external reflexion of these bodies occurs against the particles huybens compose them, and which are also larger than those of the ethereal matter, since the latter flows in their interstices. Christiaan was named after his paternal grandfather.

He recounts moreover some other properties of this Crystal; to wit, that when rubbed against cloth it attracts straws and other light things as do amber, diamond, glass, and Spanish wax. It is known that the air which surrounds us, besides the particles which are proper to it and which float in the ethereal matter as has been explained, is full also of particles of water which are raised by the action of heat; and it has been ascertained further by some very definite experiments that as one mounts up higher the density of air diminishes in proportion.

And one must imagine the same about every point of the surface and of the part within the flame. He took his observations of dark and bright spots on the surfaces of Mars and Jupiter to be evidence of water and ice on those planets. The mode of making these observations exactly is as follows. If against this row there are pushed from two opposite sides at the same time two similar spheres A and D, one will see each of them rebound with the same velocity which it had huyfens striking, yet the whole row will remain in its place, although the movement has passed along chgistiaan whole length twice over.


But by supposing springiness in the ethereal matter, its particles will have the property of equally rapid restitution whether they are pushed strongly or feebly; and thus the propagation huytens Light will always go on with an equal velocity.

He argued that extraterrestrial life is neither confirmed nor denied by the Bible, and questioned why God would create the other planets if they were not to serve a greater purpose than that of being admired from Earth.

Let the parallelogram GCFH, made by the principal section of the Crystal, as previously determined, be traced separately. This makes it evident that ilght substances yield where they meet, and spring back: This proportion, as I have said, is sufficiently precisely as 5 to 3, and is always the same for all inclinations of the incident ray.

So that the cause of the spreading of Sound is the effort which these little bodies make in collisions with one another, to regain freedom when they are a little more squeezed together in the circuit of these waves than elsewhere.

And it must be known that although the particles of the ether are not ranged thus in straight lines, as in our row of spheres, but confusedly, so that one of them touches several others, this does not hinder them from transmitting their movement and from spreading it always forward.

Furthermore these kight 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 Earth.

No trivia or quizzes yet. But Huygens went into greater detail. For I do not find that any one has yet given crhistiaan probable explanation of the first and most notable phenomena of light, namely why it is not propagated except in straight lines, and how visible rays, coming from loght infinitude chdistiaan diverse places, cross one another without hindering one another in any way.

It is then in some other way that light spreads; and that which can lead us to comprehend it is the knowledge which we have of the spreading of Sound in the air.

Published January 16th by Echo Library first published 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 chritiaan smallness; so that it appears that each little portion of the wave necessarily advances following the straight line which comes from the luminous point.

The first knowledge which cbristiaan public has had about it is due to Mr. Which matter, being present in much larger quantity than is that of the particles which compose it, was alone capable of causing transparency, according to what has been explained heretofore.

Des Cartes, who was of opinion that it is instantaneous, founded his views, not without reason, upon a better basis of experience, drawn from the Eclipses of the Moon; which, nevertheless, as I shall show, is not at all convincing. But pight 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.

Let us pass now to the explanation of the effects of Refraction, assuming, as we have done, the passage of libht of light through transparent bodies, and the diminution of velocity which these same waves suffer in them. But we must consider still more particularly the origin of these waves, and the manner in which they spread.

This, however, is contrary to experience, since the huygenw GEC would be very sensible, and about 33 degrees. Lists with This Book. After all, this prodigious quantity of waves which traverse one another without confusion and without effacing one another lkght not be deemed inconceivable; it being certain that one and the same particle of matter can serve for many waves coming from different sides or even from contrary directions, not only if it is struck by blows which follow one another closely but even for those which act on it at the same instant.


I found also that when QRE made a straight line, that is, when the incident ray entered the Crystal without being refracted as I ascertained by the circumstance that then the point E viewed by the extraordinary refraction appeared in the line CD, as seen without refraction I found, I say, then that the angle QRG was 73 degrees 20 minutes, as has been already remarked; and so it is not christiaan ray parallel to the edge of the Crystal, which crosses it in a straight line without being refracted, as Mr.

As to those which can be made here on the Earth, by striking lights at great distances, although they prove that light takes no sensible time to pass over these distances, one may say with good reason that they are too small, and that the only conclusion to be drawn from them is that the passage of light is extremely rapid.

Upon a leaf of paper fixed on a thoroughly flat table there is traced a black line AB, and two others, CED and KML, which cut it at right angles and are more or less distant from one another according christiaab it is desired to examine a ray that is more or less oblique.

To find the length of the line N, in proportion to CP, CS, CG, it must be determined by observations of the irregular refraction which occurs in this section of the crystal; and I find thus that the ratio of N to GC is just a little less than 8 to 5.

For the force of these waves must grow feeble in proportion as they move away from their origin, so that the action of each one in particular will without doubt become incapable of making itself felt to our sight. For since it passes through them continuously and freely, it follows that they are always full of it. It is true that we are here supposing a strange velocity that would be a hundred thousand times greater than that of Sound.

Treatise on Light, by Christiaan Huygens

But it occurs also in other countries, for I have had some of the same sort which had been found in France near the town of Troyes in Champagne, and some others which treatisd from the Island of Corsica, though both were less clear and only in little bits, scarcely capable of letting any effect of refraction be observed.

Descartes was impressed by his skills in geometry. From this it will be seen with what facility, following our new Theory, we find not only the Ellipses, Hyperbolas, and other curves which Mr. Thanks for telling us about the problem.

Treatise on Light by Christiaan Huygens

The demonstration of this is, it will be seen, entirely similar to that of which we made use in explaining ordinary refraction. Hugens has given us, and with which he has performed so many beautiful experiments. Huygens was a leading scientist of his time. And none can read his investigation of the phenomena found in Iceland spar without marvelling at his insight and sagacity.