Academia scientiarum, or, The academy of sciences being a short and easie introduction to the knowledge of the liberal arts and sciences, with the names of those famous authors that have written on every particular science : in English and Latine / by D. Abercromby ...

Sect. X. Dioptrick.

DIoptrick is that part of Astrology that searcheth out by Instruments the distance of the Sun, Moon, and other Planets. If you take it more generally, its chief end is to shew the apparent chan∣ges of our sight, and of visible objects look'd into through Prospective glasses.

It treats of the broken or refracted Rays of light, and this is its chief prin∣ciple: When a Ray passeth through a thin middle into a thicker, it breaks in the Superficies of the thicker towards the perpendicular line; and when it pas∣seth through a thick middle, or medium, to a thinner it deviates from the perpen∣dicular line, which this obvious experi∣ment demonstrates. Lay an Image, or any other visible object, in the bottom of a Vessel, and then go back till it vanish out of your sight; now if you fill this Ves∣sel

with water, it shall presently be vi∣sible again, because the Ray coming from your eye, breaks downwards in the superficies of the water, as the same going streight up to the superficies of the water deviates from the perpendicu∣lar, because of the thinner air towards the eye, which renders the object visible again.

This Science treats likewise of Con∣vex and Concave glasses, as they may work some change in the sight, and may help it. It gives▪ an account of those whom Aristotle calls 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, who see remote things distinctly, and nearer ob∣jects confusedly; and why those whom we call 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, see both the remote and nearer objects confusedly.

It teacheth likewise amongst other things, 1. That those whom we call 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 see distinctly some things that are represented by Convex glasses in a streight situation. 2. That they see not distinctly through a Convex glass any of those objects that are overturn'd.

3. It sheweth the influence of Glasses ap∣plied one to another upon our sight.

Authors.

Kepler, Maurolycus, Euclide, &c. have written of this curious Science.