Page:Rulesexamplesofp00pozz.djvu/20

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PREFACE.


to the middle Line, is alſo here laid down: And by our Author's Method, Horizontal Perſpective, or that of Ceilings, is render'd leſs difficult than the Vertical, or that againſt an upright Wall. Upon the whole, nothing ſeems wanting that may make a Work of this nature complete; unleſs what concerns Deſigns which are either Circular, or abound with many Columns: For the Performance whereof, the Author, as he promiſes in the Sixty-fifth Figure, has, in a SECOND Volume, given a Rule more proper for the purpoſe; which alſo may poſſibly be made Engliſh in due time, if this Part meet with Encouragement.

What the Author once intended ſhould make a Part of that Second Volume, he afterwards inſerted in the Ninety-third and following Figures of this Book: In the laſt of which, particular Notice ſhould be taken of his Conclusion; That if Painters would not run into inextricable Errors, they ought as ſtrictly to obſerve the Rules of Perſpective, in deſigning the Figures of Men and Animals, as they do in painting Columns, Cornices, or other Tarts of Architecture.

That none therefore be diſcourag'd in their firſt: Attempts, thro' the Brevity or Silence of our Author, (who, writing in a Country where the Principles of this Art are more generally known than with Us, had no need to inſiſt ſo long on ſome things, as might be thought neceſſary to Beginners) we ſhall endeavour to ſpeak as plainly as we can to a Point or two, moſt liable to be miſunderſtood, or to prove a Stumbling-Block at the Entrance 3 and then add a Word of Advice to ſuch as ſhall attempt the putting theſe Rules in Execution.

The Author, in both his Explanations of the firſt Plate, has given ſome Account of what he would have his Reader underſtand, by Deſigning in Perſpective: and a right Conception of this Point being of great Uſe to facilitate the Work, we thought it not improper, to deſcribe ſomething more particularly, what is meant by the Art Perſpective; but ſhall at preſent ſpeak only of That, which, whether Vertical or Horizontal, is receivd on a Flat and Even Superficies: This being of much the more general Uſe; and, when rightly underſtood, renders the Difficulties of the Circular or Irregular Surfaces, eaſy and familiar.

PERSPECTIVE is the Art of Delineating, on a flat Superficies, as a Wall, Ceiling, Canvas, Paper, or the like, the Appearances of Objects, as ſeen from One determinate Point: For tho in Works of great Length, Two, Three, or more Points of Sight are ſometimes made uſe of; yet ſuch may more properly be ſaid to be Several Views conjoin'd, than One Piece of Perſpective: Of which ſee the Author's Opinion, at the End of this Treatiſe.

In Perſpective, the Eye of the Beholder is eſteem'd a Point, from whence Rays are ſuppos'd to proceed to every Angle of the Object. The Wall or Canvas to be painted (which we ſhall here call the Section) is imagin'd to intervene at right Angles to the Axis of the ſaid Rays; and by directing them, to receive the Appearance of the Object, in greater or leſs Proportion, as the Section is more or leſs remote from the Point of Sight. Our Author's Rule is, That the Diſtance of the Eye ought to be equal to the greateſt

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