TO THE EARNEST READER ‣

There are two matters, earnest Reader, about which we have decided you should be briefly advised here. The first is that we have enclosed those things which we have inserted throughout the text of Alhazen original: "Albazeno," the Latinized name for the 11th-century polymath Ibn al-Haytham as a commentary within two brackets (as they are called), like this: [ ]. The second is that we have used a certain brevity concerning original: "περὶ τὴν," Greek for 'concerning' the citations of various geometers used in the foundations of the demonstrations. Indeed, we have noted the propositions of Euclid, omitting his name, in this manner: by 29 p 1. l. ax. 4 original: "per 29 p 1. l. ax. 4", meaning: by the 29th proposition of the 1st book: axiom 4. Or similarly, p 1 l ax. 4, meaning: proposition 1, definition 6 of the book of Euclid's Elements, and so on. In the citations of other geometers, we have similarly added the numbers of the theorem and the book, with the letters th (signifying theorem) placed between the numbers along with the author’s name. For the propositions of Alhazen (into which the work was divided by us), for the sake of distinction and brevity in citing both Euclid and Alhazen, we have called them "numbers": and they are noted by us thus: by 19 n 1. 14 n 2. 13 n., meaning: by number 19 of the 1st book of Alhazen’s Optics; number 14 of the 2nd book; number 13: of that same book, of course, in which the citation occurs. That is, by number 13 of the first, second, third, etc., book of Alhazen’s Optics, if that number is cited within that same book. As for what pertains to errors, it pleased us to list them at the entrance of the book, so they would be ready for anyone wishing to correct them; where the first number indicates the page, and the second indicates the line.

Page 4. line 55: center. 7. last line: each. 16. 35: last. 26. 22: of them. 34. 23 & 24: humidity. 41. 46: certainty. 61. 1: for 711, read 111. 67. 16: to be formed. 80. 60: position. 81. 82: the locations of the figures have been swapped. 83. 56: position. 93. 28: after "again," add "in". 106. 53: in both. 111. 10: of light. 134. 60: angle, act. 135. 14: after "lines" put a colon, and after "reflection," a comma. 142. 11: by sight and the visible. 146. 31: will meet. 156. 49: for 44 after "outer," substitute 45. 159. 26: equidistant. 181. 36 & 37: for "there," read "where". 185. 12: for t, b. 189. 6: let it be. 194. 53 & 54: for œ, œ d. ibid. 62: for "i" after "a g," substitute "&". 197. 15: for 4, read 45. Page 201: the first figure of this number, which is on the left, pertains to the preceding number 14; for the logic of the layout (as they call it) did not permit each to be placed in its own spot. 205. 1: z q l. 211. 21: remove the comma after "l e". 213. 43: mirrors. 217. 39: for 4, read 41. 219. 39: for "it will be," read "it will be reflected," and for "in," read "from". Page 221: in the figure, the letter immediately below 'r' on line 'g r' is 'k', though it is obscured because of the intersection of lines. 223. 17: periphery a z. 226. 28: let it arrive therefore. 229. 58: passing through. 237. 21: after "of the plate" add: "and between the surface of the plate". Ibid. 35: delete "let it be". 240. 46: they exist. 250. 55: line. 252. 7: after "elevation," put a comma. Ibid. 19: k b g. Ibid. in the figure, let the letter 'a' be placed across from 'e', the center of the world, at the periphery of the meridian b g. Ibid. 49: they exist. 255. 57: for "in," read "a". 258: in the second figure at the end of the extended line f o, place the letter 'q'. 266. 48: remove "&". Page 273: in the first figure at the end of the extended line d m, place the letter 'e'. Page 275: under number 45, two figures are joined together, of which the latter, on the right, pertains to number 46: to which the previous figure of number 47 should also be referred. 281. 38: delete the comma after "different". 285. 23: for e, read ei. 286. 51: they remain. 288. 58: for 48, read 40. Finally, it also pleased us to put back in the errata what was omitted in the commentaries to the fourth and third figures of number 64: namely: [When the image is seen at point a: and b q, which is drawn parallel to a l, falls outside the triangle a g: then, omitting b q and having shown the equality of lines a g, a t, as before, the proposition will be concluded more briefly through proposition 3, book 6 original: "per 3 p 6," likely referring to Euclid's Elements. For as b e is to e a, so b g is to a g, that is, through prop 7, book 5 original: "per 7 p 5" to a l: but as b g is to a l, so b t is to t a because of the similarity of triangles b g t, a l t. Therefore, through prop 11, book 5 original: "per 11 p 5", as b e is to e a, so b t is to t a. In the same way, with b q falling inside the triangle a g t, the demonstration will be shorter and easier without line a l.]