Page:Rulesexamplesofp00pozz.djvu/21

PREFACE. Extent of the Object, whether in Length or Height: As, to view a Building that is a hundred Foot long, and fifty high; he would have the Ditance a hundred Foot: To view a Tower ixty Foot wide, and a hundred and fifty Foot high 3 the Diftance fliould be a hundred and fifty Foot. This Ditance is not trictly to be undertood of the Space between the Eye and the Object, but of the Space between that and the Section, the Plan of which our Author calls the Line of the Plan, or Ground-line • for it's often requifite, that the Section be plac'd at ome Ditance before the Object, on account of Projectures of Cornices, and other Parts of the Work that advance, as in the Eighth Figure.

Place of the Eye, with repect to its Height above the Ground, ought to be uch, as is mot natural and agreeable to the Object. Thus in Architecture, the Baements and inferior Parts of a Building are improper to be et above the Eye, and their Cornices and Entablatures have but an ill Effect when below it. General Perpectives indeed require the Sight to be taken at a Bird's View 3 and on other Occaions the Place of the Eye may be vary'd: but the bet and mod general Rule is, not to exceed five or ix Foot Height above the Ground. The Height of the Eye above the Ground, thro' which a Line is drawn, call'd the horizontal Line, is et on by the ame Scale of Proportion, as the Deign bears to the real Work; and the Point of Sight o plac'd therein as may render the Object mot agreeable. From the Point of Sight, either on one or both ides in the horizontal Line, you are to et, by the ame Scale, the Ditance you tand from the Section. And by means of thee Points of Sight and Ditance, and the Meaures of the Parts brought on the Lines of the Plan and Elevation of the Section by the ame Scale; all the Examples of this Volume are reduc'd into Perspective; as is manifet on Inpection of the Figures.

we would add, by way of Advice, is,

I. you very carefully oberve, what the Author undertands by Breadth, Length, and Height, in his Explanation of the Fifth Plate, before you proceed to practie on any Figure 3 otherwie you'll certainly miundertand him, pecially in the Third Figure.

II. the Rules of the Tenth and Eleventh Figures be particularly regarded, for avoiding Confuion in the Plans and Uprights.

III. from the Dipofition of the Perpective-Plans and Uprights, with repect to the finih'd Pieces in the Twelfth and many following Figures, you would oberve with what Dipatch the aid Pieces may, without the help of Compaes, be delineated by your Drawing-Square; viz. the Perpendiculars from the Perpective-Plan, and the level Lines from the Perpective-Upright, or Section.

IV. That you would accutom yourelf in Works that have many Lines, to make the Perpective-Plans and Uprights for each Part ditinct, o as to prevent all Danger of Confuion. Thus you may have one Plan and Upright for the Baement of a Building; and when that is drawn on your finih'd Piece, remove them, and place thoe of the Body of the Houe; and when that's complete, do o by the Attick, &c. always oberving