CANDID READER

A small decorative pointer element follows the title.

There are two things, candid Reader, about which we have thought it necessary to warn you here in a few words. The first is that we have enclosed those things which we have inserted in place of commentaries in Alhazen with two clauses (as they are called), thus [ ]. The second is that we have used a certain graphic brevity when citing the foundations of demonstrations from various geometers. Indeed, we have noted the propositions of Euclid without the name in this manner: "per 29 p 1. 1 ax. 4. p. 1 d 6," which means: by the 29th proposition of the 1st book, axiom 4, proposition 1, definition 6 of the 6th book of Euclid’s Elements, etc. In the citations of the other geometers, we have similarly added the numbers of the theorem and the book, with the letters "th" (signifying theorem) placed between them, along with the name. However, for the propositions of Alhazen (into which he has been divided by us), for the sake of distinction and brevity in citing the propositions of Euclid and Alhazen, we have called them "numbers." Thus, they are noted by us in this way: "per 19 n 1. 14 n 2. 13 n," which means: by the 19th number of the 1st book of Alhazen’s Optics, the 14th number of the 2nd book, the 13th number: namely, of that book in which this citation is made; that is, by the 13th number of the first, second, third, etc., book of the Optics of Alhazen, if that number is cited in the first, second, third, etc., book of Alhazen's Optics. As for the errata, it pleased us to write them down in the vestibule of the book so they would be ready for one wishing to make corrections: where the first number indicates the page, and the second the line.

Page 4, line 55, centrum center. 7, last, unaquaq; each one. 16, 35, ultimum last. 26, 22, earum of them. 34, 23 & 24, humiditas humidity. 41, 46, certitudine certainty. 61, 1, instead of 71, 111. 67, 16, formarū of forms. 80, 60, positio position. 81, 82, the locations of the figures have been swapped. 83, 56, positio position. 93, 28, after iterū again, add in. 106, 53, utroq; in both. 111, 10, lucis of light. 134, 60, angulus a g e angle a g e. 135, 14, after lineis lines place a colon, and after reflexionis of reflection, a comma. 142, 11, visu & visibili sight and the visible. 146, 31, concurret will concur. 156, 49, instead of 44 after exteriore exterior, replace with 45. 159, 26, æquidistans equidistant. 181, 36 & 37, instead of ibi there, ubi where. 185, 12, instead of t, b. 189, 6, fit it is made. 194, 53 & 54, instead of œ, œ d. Ibid, 62, instead of i after a g, replace with &. 197, 15, instead of 4, 45. Page 201, the prior figure of the 15th number, which is to the left, pertains to the preceding 14th number; for the method of "composition," as they call it, did not allow each to be placed in its own spot. 205, 1, z q l. 211, 21, after l e remove the comma. 213, 43, speculis mirrors. 217, 39, instead of 4, 41. 219, 39, instead of erit it will be, reflectetur it will be reflected, and instead of in in, ex out of. Page 221, in the figure, the letter immediately below r in the line g r, which is darker due to the convergence of lines, is k. 223, 17, peripheria a z periphery a z. 226, 28, perueniat ergo therefore let it arrive. 229, 58, transeunte passing through. 237, 21, after laminæ plate add: & between the surface of the plate. Ibid, 35, delete fit it is made. 240, 46, existunt they exist. 250, 55, lineam line. 252, 7, after eleuatio elevation, place a comma. Ibid, 19, k b g. Ibid, in the figure, place the letter a in the region of e, the center of the world, to the periphery of the meridian b g. Ibid, 49, existunt they exist. 255, 57, instead of in in, a. 258, in the second figure at the terminus of the line f o extended, place the letter q. 266, 48, remove &. Page 273, in the first figure at the terminus of the line d m extended, place the letter e. Page 275, under number 45, two figures are joined, the latter of which, which is to the right, pertains to the 46th number; to which the prior figure of the 47th number also ought to be referred. 281, 38, after diuersæ diverse delete the comma. 285, 23, instead of e, ei. 286, 51, restant remain. 288, 58, instead of 48, 40. Finally, it pleased us to also replace in the errata that which was omitted in the commentaries to the fourth and third figures of 64 n 5: namely. [When the image is seen at point a: and b q, which is drawn parallel to a l, falls outside the triangle a t g: then, with b q omitted and the equality of the lines a g, a t shown as before, it will be concluded more briefly by 3 p 6 of the propositions. For it will be as b e is to a e, so is b g to a g, that is, by 7 p 5 to a l: but as b g is to a l, so is b t to t a on account of the similarity of the triangles b g t, a l t. Therefore, by 11 p 5, as b e is to a e, so is b t to t a. In the same way, when b q falls within the triangle a g t: the demonstration will be shorter and easier without the line a l.]