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. XXIII. Opticks.

THE Opticks, or Optica, gives us an account of various appea∣rances of Objects. This Science treats of the streight Ray, as the Catoptrick of the reflected, and the Dioptrick of the refracted or broken Ray. These follow∣ing Definitions belong to the Opticks. The proper Objects of Sense, are those that can be known but by one sense; and the common Objects, such as may be known by more than one sense. Light and Colour, are the proper Objects of our sight; the Light, upon its own ac∣count; and the Colour, by the help of Light. These following things, are the common Objects of our Senses, Bulk, Figure, Place, Situation, Distance, Continuity, Discontinuity, Motion, and Rest. The visuel Rays, are the streight lines, by which the frame of the visible Object is in a manner carried to the eye.

We may reckon among the chief prin∣ciples of this Science, these following.

The visible object radiates from all its least parts, to all the least parts of the Medium, to which one may draw a streight line.

That is seen, and that only, from which to the eye the visuel Ray may be eztended.

The more bodies there appear between the eye and the object, the more remote the objects appear to be.

The Convergent Rays, are those that departing from the object, come to∣gether: Such are, the Rays of diverse parts of the object, which cut one another in the Chrystalline humor. The Divergent Rays, departing from the object towards the eye, recede from one another: The Rays of every point of the object, are divergent, till they come to the Chrystalline humour, beyond which they come together again towards the Retina.

We may reckon these following Pro∣positoins amongst the most considerable of the Opticks.

No visible object is seen at first alto∣gether, and perfectly.

Magnitudes being in the same streight line, the remoter seem to be the lesser.

Parallel intervals seem to be nearer one another, the farther they are from the eye.

Rectangle Magnitudes being seen at a distance, seem to be round.

Equal Magnitudes being under the eye, those that are farthest from the eye, seem to be highest.

Authors.

You may reckon amongst the best Ma∣sters of the Opticks, Euclid, Aquilo∣nius, Scheiner, Vitellio, Alhazane, Herigone, &c.