[ [90] See chap. cccxvii.
[ [91] This position has been already laid down in chapter cxxiv. (and will also be found in chapter cccxlviii.); and the reader is referred to the note on that passage, which will also explain that in the text, for further illustration. It may, however, be proper to remark, that though the author has here supposed both objects conveyed to the eye by an angle of the same extent, they cannot, in fact, be so seen, unless one eye be shut; and the reason is this: if viewed with both eyes, there will be two points of sight, one in the centre of each eye; and the rays from each of these to the objects must of course be different, and will consequently form different angles.
[ [92] The braccio is one foot ten inches and seven eighths English measure.
[ [93] i.e. To be abridged according to the rules of perspective.
[ [94] See chap. cxxii.
[ [95] The whole of this chapter, like the next but one preceding, depends on the circumstance of there being in fact two points of sight, one in the centre of each eye, when an object is viewed with both eyes. In natural objects the effect which this circumstance produces is, that the rays from each point of sight, diverging as they extend towards the object, take in not only that, but some part also of the distance behind it, till at length, at a certain distance behind it, they cross each other; whereas, in a painted representation, there being no real distance behind the object, but the whole being a flat surface, it is impossible that the rays from the points of sight should pass beyond that flat surface; and as the object itself is on that flat surface, which is the real extremity of the view, the eyes cannot acquire a sight of any thing beyond.
[ [96] A well-known painter at Florence, contemporary with Leonardo da Vinci, who painted several altar-pieces and other public works.
[ [97] See chap. cxxiv. and cccxlviii.
[ [98] See chap. x.
[ [99] See chap. cci.