Christiani Hugenii Zelemii, dum viveret, toparchae opuscula postuma, quae continent dioptricam. Commentarios de vitris figurandis. Dissertationem de corona & parheliis. Tractatum de motu. De vi centrifuga. Descriptionem automati planetarii

...inserted into the French Journal des Sçavans Journal of the Learned on January 29th and February 26th of the year 1680, and while the Astroscopia was published publicly by the Author himself, nothing concerning the Reflecting Telescope of Newton original: "Speculare telescopium Newtoni" has come into our hands. Now, in this Dioptrics, he frequently uses quite lengthy demonstrations based on compound ratios; for this reason, we hesitated for a long time as to whether it would be better to append some brief demonstrations based on calculation, which Huygens undoubtedly used in arriving at his conclusions. But since he preferred the method of demonstrating through the composition of ratios in almost all his other works, we abandoned this plan, thinking ourselves bound to comply with the Author's will as far as we could ascertain it by probable conjecture. We did find our own notes indicating that many things ought to be condensed or changed. However, since it was uncertain whether we would correctly grasp his intent in making such changes, we deemed it best to follow the text itself as much as possible. Nevertheless, when we noticed that the Propositions were not arranged with sufficient conciseness in many places, and it seemed the Author had not reached a final decision about them, we arranged them in a way that seemed more convenient for the series of topics being discussed and for the proper order of the demonstrations.

In his Dioptrics, our author begins with the primary foundations, namely the very measurement of refraction, according to which rays passing from air into either water or glass are refracted. Then he provides the rules by which the points of collection or dispersion of rays are found, whether passing through the flat or spherical surfaces of various media, or through any lenses whatsoever. Nor does he treat only those things which are on the axis itself, but also those found to the sides outside the axis. Yet, in truth, since lenses consisting of a spherical figure on both sides, or of a spherical and a flat side, do not collect rays accurately, but only approximately...

A decorative printer's ornament consisting of two asterisks.