E-text prepared by Clare Boothby, Stephen Schulze,
and the Project Gutenberg Online Distributed Proofreading Team
TREATISE ON LIGHT
In which are explained
The causes of that which occurs
In REFLEXION, & in REFRACTION
And particularly
In the strange REFRACTION
OF ICELAND CRYSTAL
By
CHRISTIAAN HUYGENS
Rendered into English
By
SILVANUS P. THOMPSON
University of Chicago Press
PREFACE
wrote this Treatise during my sojourn in France twelve years ago,and I communicated it in the year 1678 to the learned persons who thencomposed the Royal Academy of Science, to the membership of which theKing had done me the honour of calling, me. Several of that body whoare still alive will remember having been present when I read it, andabove the rest those amongst them who applied themselves particularlyto the study of Mathematics; of whom I cannot cite more than thecelebrated gentlemen Cassini, Römer, and De la Hire. And, although Ihave since corrected and changed some parts, the copies which I hadmade of it at that time may serve for proof that I have yet addednothing to it save some conjectures touching the formation of IcelandCrystal, and a novel observation on the refraction of Rock Crystal. Ihave desired to relate these particulars to make known how long I havemeditated the things which now I publish, and not for the purpose ofdetracting from the merit of those who, without having seen anythingthat I have written, may be found to have treated [Pg vi]of like matters: ashas in fact occurred to two eminent Geometricians, Messieurs Newtonand Leibnitz, with respect to the Problem of the figure of glasses forcollecting rays when one of the surfaces is given.
One may ask why I have so long delayed to bring this work to thelight. The reason is that I wrote it rather carelessly in the Languagein which it appears, with the intention of translating it into Latin,so doing in order to obtain greater attention to the thing. Afterwhich I proposed to myself to give it out along with another Treatiseon Dioptrics, in which I explain the effects of Telescopes and thosethings which belong more to that Science. But the pleasure of noveltybeing past, I have put off from time to time the execution of thisdesign, and I know not when I shall ever come to an end if it, beingoften turned aside either by business or by some new study.Considering which I have finally judged that it was better worth whileto publish this writing, such as it is, than to let it run the risk,by waiting longer, of remaining lost.
There will be seen in it demonstrations of those kinds which do notproduce as great a certitude as those of Geometry, and which evendiffer much therefrom, since whereas the Geometers prove theirPropositions by fixed and incontestable Principles, here thePrinciples are verified by the conclusions to be drawn from them; thenature of these things not allowing of this being done otherwise.
It is always possible to attain thereby to a degree of probabilitywhich v