CAP. XXIII.
Of Perspective.
PRospective (being a Species of Geometry) is a Science treat∣ing of Visible Lines, and may be divided into three parts, Optica, Sciographica and Specularia.
Optica of two kindes, either Physiological or Grammical.
The Physiological part scearcheth the Vniversal Principles, Causes and Elements of the appearences of things which may be considered three several ways, as Vision is Direct, Reflected or Refracted as when things are seen in Water, Glasses &c.
The Grammical is the Art of Delineation, and is more Ne∣cessary to Painting then the other. It considereth Sight either True or False, and is of three sorts, Anoptica, Optica and Catoptica.
Anoptica is the Art of Delineating Objects elevated above the Horizon, Optica designs those extended Foreright, level with Horizon, and Catoptica those beneath the Horizon, which appear as if they came nearer the Eye below.
Another Species is call'd Sciogrophica; It handleth the Causes, Principles, Elements, and Properties of Shaddows; giving the Reason of the Variety of the Apparitions of the Shapes and I∣mages of Things, according as they are elevated either above, direct against, or beneath; far of or near the Eyes and as by the Laws of Grammica are distributed the Out lines of the Superficies as they ought to be, according to their distance and Situation: so this part considereth the Shaddows of Bodys, ac∣cording as their Superficies are Protuberant, or Depress'd.
The last Species is Specularia, and considereth the Reflections and Refractions of Beams, giving Directions for making Glasses, Page 60 either Plane, Convex, Concave, Pyramidal, Angular, Inverting Erecting, &c. which I shall wave, as not being so Pertinent to this Art.
The Eye is the Foundation of Perspective, because thence the Natural and the Rational Sight is Formed: Natuaral where∣in the shapes of Things seen do come to it simply, by the Beams of light; Rational, wherein there is farther Consider'd the Rea∣son and Effect of the Sight, even where the Eye cannot be o∣therwise plac'd then by supposition, as at an infinite di∣stance, &c.
The Eye is call'd by some Italian Authours, the Term; because by it all Things in a Picture are Limited, and any Thing made without the disposition of this Term, cannot be true, as not being dispos'd for the Sight, nor order'd ac∣cording to the Visuall Beames, coming to the Eye from the whole.
It is call'd also the Center because all the Lines of the Base and Circumference of the Object do meet in it, as in a Circle all Lines run from the Circumference to the Center.
It may be consider'd also as the Apex of a Pyramide; be∣cause all the space between the Object and the Lines or Beams which pass along, and are extended from the extremitys of the Object to the Eye end therein, as in the Point of a Pyramide, and the Eye together with the Intellect ought to judge of the true Forms of things, to the end it may be able to Imitate them perfectly.
In Distance we must observe that the Object come not too near to the Eye, nor yet be too far of, for then the Air be∣tween will take away too much of the Colour and Beauty.
In too Obtuse and short Distances, Things seem to decline and run too much backwards, in a preposterous manner; so Things too far of, making Acute and sharpe Angles in the Eye give no grace to the work; it is reckon'd a proper Di∣stance, for the Beholder to stand from the Object, three times the Length thereof.
Next we will consider the Object which is the Thing that standeth before our Eyes; the first Figure to be observ'd is cal'd the Natural, and must be exprest in the first and prin∣cipal Page 61 part of the Picture: so that whatever you place inwards, towards the Eye of the work, must be diminish'd, according as the Lines and Beames shall extend themselves.
Now we will consider the three sorts of Sight, and first A∣noptica, which is the Real and Upper Line, by help whereof we consider all the parts of the Object above the Horizon, and therby bringeth them to the Intersection, or Line of Shortning; whence according to the situation of the Body, the hinder parts are made to run downwards and the nearest parts to rise upwards, and from hence the Declinings and Arisings, the Shortnings and In∣creasings of the parts of the Body are caused.
This Line hath his Original from the Center or the begin∣ning of the Distance, which is the Eye; so it returns to the same through the midst of the Beams, which couple all the Extreem Limits of the perfect Body.
Optica is the second Real Sight and Direct Line, and is that which is nearest the Object, so that the upper parts of the Ob∣ject belong to the foremention'd Line, and the lower to Catop∣tica; this is that therefore which principally touches all parts of the Object both above and below, and therefore it is call'd the Direct Line.
For the Beams parting themselves strongly at the Eye and falling on the nearest parts of the Object, end there, causing the upper and lower parts to be shortned and diminish'd and the E∣minences to hide the Concavities, and the larger parts to co∣ver the narrower, making the Object to encrease and diminish according to their respective distances from the Perpendicular, in the due observance whereof consisterh the chief Difficulty as well as Beauty of the Art.
Catoptica is the third sort of Sight whose beams touch all the lower parts of the Object, conducting them to the Point of Intersection, so that when the Object is below the Eye, the farthest parts seem to rise and the nearest to decline down∣wards.
