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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Now if about the centres A, B, one describes the circles DK, EL, which represent the spreading of the waves which originate from these two points, and if one draws the straight line KL which touches these two circles, it is easy to see that this same line will be the christiana tangent to all the other circles drawn about the centres F, H, etc.

Treatise on Light, by Christiaan Huygens

For we have stated before this, that the line N being the radius of a spherical wave of light in air, while in the crystal it spread through the spheroid ABPS, the ratio of N to CS will beto 93, Des Cartes gives for the spring, though I do not, like him, suppose the pores to be in the form of round hollow canals. 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 christiana, 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.

This wave is then represented by the circumference SNR, the centre of which is A, and its semi-diameter equal to two-thirds of CB. And I do not believe that this movement can be better explained than by supposing that all those of the luminous bodies which are liquid, such as flames, and apparently huyvens sun and the stars, are composed of particles which float in a much more subtle medium which agitates them with great rapidity, and makes them strike against the particles of the ether which surrounds them, and which are much smaller than they.

As to this it is to be remarked that there is a law of motion serving for this propagation, and verifiable by experiment. However, one will see hereafter that we have to suppose such an equality not so much as a necessity for chrishiaan propagation of light as for rendering that propagation easier and more powerful; treatisw it is not beyond the limits huygenw probability that the particles of the ether christiaa been made equal for a purpose so important huhgens 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.

Because also of them the Sun and the Moon appear as risen before in fact they have, and appear to set later: So on the other hand the external reflexion of these bodies occurs against the particles which compose them, and which are also larger than those of the ethereal matter, since the latter flows in their interstices.

Wherefore I here desire to propound what I have meditated on the subject, so as to contribute as much as I can to the explanation of this department of Natural Science, which, not without reason, is reputed to be one of its most difficult parts. This, however, is contrary to experience, since the teatise GEC would be very sensible, and about 33 degrees.

Then if one considers in order the other pieces H of the wave AC, it appears that in the same time that the piece C reaches B they will not only have arrived at the surface AB along the straight lines HK parallel to CB, but that, in addition, they will have generated in the diaphanous substance from the centres K, partial waves, represented here by circumferences the semi-diameters of chirstiaan are equal to two-thirds of the lines KM, that is to say, to two-thirds of the prolongations of HK down to the straight line BG; for these semi-diameters would have been equal to entire lengths of KM if the two transparent substances had been of the same penetrability.


Hence it christiaaan that the time along ABC is the shortest possible; which was to be proven. It is founded as is the preceding argument upon celestial observations, and proves not only that Light takes time for its passage, but also demonstrates how much time it takes, and that its velocity is even at least six times greater than that which I have just stated.

And if these contrary movements happen to meet one another at the middle sphere, B, or lighf some other such as C, that sphere will yield and act as a spring at both sides, and so will serve at the same instant to transmit these two movements.

Des Cartes, that light passes more slowly through glass and water than through air. To explain then the reasons of these phenomena according to our principles, let AB be the straight line christjaan represents a plane surface bounding the transparent substances which lie towards C and towards N. For this he makes use of the Eclipses suffered by the little planets which revolve around Jupiter, and which often enter his shadow: 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 tgeatise it appears that each little portion of the wave necessarily advances following the straight line which huyens from the luminous point.

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But the tower E, which is beneath this curve, does not hinder the point A from being seen. For, the point H having been found and marked, as aforesaid, directly above treztise point E, I observed the appearance of the line CD, which is made by the extraordinary refraction; and having placed the eye at Q, so that this appearance made a straight line with the line KL viewed without refraction, I ascertained the triangles REH, RES, and consequently the angles RSH, RES, loght the incident and the refracted ray make with the perpendicular.

Similarly if the Earth be AB, and the top of the Atmosphere CD, which probably is not a well defined spherical surface since we know that the air becomes rare in proportion as one ascends, for above there is so much less of it to press down upon itthe waves of light from the sun coming, for instance, in such a way that so long as they have not reached the Atmosphere CD the straight line AE lifht them perpendicularly, they ought, when they enter the Atmosphere, to advance more quickly in elevated regions than in regions nearer to the Earth.

This, in my opinion, we must necessarily do, or else renounce all hopes of ever comprehending anything in Physics. I will set it forth, in a way a little different from his, in order to make the conclusion tratise comprehensible. This, then, being thus disposed, and taking CM atparts, I found by the calculation which will be given at the end, the semi-major diameter CP to be , and the semi-axis CS to be 93, the ratio of which numbers is very nearly 9 to 8; so that the spheroid was of the kind which resembles a compressed sphere, being generated by the revolution of an ellipse about its smaller diameter.

Treatise on Light by Christiaan Huygens

There may be numerous typos or missing text. Now according as the air near the Earth exceeds in density that which is higher, the curvature of the ray AEB becomes greater: For if what we have just said is true: But the movement of the Light must originate as from each point of the luminous object, else we should not be able to perceive all the different parts of that object, as will be more evident in that which follows. And this suffices to show that the ray will continue along the curved line which intersects all the waves at right angles, as has been said.


His main discoveries are the centrifugal force, collision laws for bodies and the argument that light consists of waves. Now there is no doubt at all that light also comes from the luminous body to our eyes by some movement impressed on the matter which is between the two; since, as we have already seen, it cannot be by the transport of a body which passes from one to the other.

Kreger rated it it was ok Nov 04, First, then, if the ethereal matter cannot penetrate transparent bodies at all, their own particles would be able to communicate successively the movement of the waves, the same as do those of the Ether, supposing that, like those, they are of a nature to act as a spring. Thus this infinite number of waves which originate at the same instant from all points of a fixed star, big it may be as the Sun, make practically only one single wave which may well have force enough to produce an impression on our eyes.

It remains then that they are, as has been said, assemblages of particles which touch one another without constituting a continuous solid. Similarly at the other quadrature when the earth has come to E from D while approaching toward Jupiter, the immersions of the Satellite ought to be observed at E earlier than they would have been seen if the Earth had remained at D.

Erasmus Bartholinus, who has given a description of Iceland Crystal and of its chief phenomena. Whence I understood the reason why this substance, though so transparent, is useless for Telescopes, when they have ever so little length.

But this angle EAF is scarcely ever more than half a degree because the attenuation of the vapours alters the waves of light but little. His mother was Suzanna van Baerle. He liked to play with miniatures of mills and other machines.

Treatise On Light

But what may at first appear full strange and even incredible liyht that the undulations produced by such small movements and corpuscles, should spread to such immense distances; as for example from the Sun or from the Stars to us. It must even occupy much less of it, since quicksilver is less heavy than gold, and the matter of gold is by no means dense, as follows from the fact that the matter of the vortices of the magnet and of that which is the cause of gravity pass very freely through it.

Whence then, one will say, does their opacity come? Taking, then, the parallelopiped AFB, of which the obtuse solid angle C is contained between the three equal plane angles, and imagining in it the three principal sections, one of which is perpendicular to the face DC and passes through the edge CF, another perpendicular to the face BF passing through the edge CA, and the third perpendicular to the face AF passing through the edge BC; I knew that the refractions of the incident rays belonging to these three planes were all similar.

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. But there is one experiment which renders this refraction very evident; which is that of fixing a telescope on some spot so that it views an object, such as a steeple or a house, at a distance of half a league or more.

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. It is not necessary to examine here the causes of this hardness, or of that springiness, the consideration of which would lead us too far from our subject.