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21.

the Ap addition p /addition arent angle from the middle column is about one Whole degree greater than the Apparent Angles of Either of the other two Extreme columns. Also the angle dEc is equal to the angle gEh, & fEe, equal to KEi. by construction.

Therefore (by Cor. 2. Theorem 2, Brook Taylors perspective. " The Original of ae " projection may be any Object, that will- " produce the same cone of rays.

Hence the Originals of the projections fe, dc, may be any lines ki, or lm, gh, or no, producing the same optic Cone. but Gm, is a Tangent, to the radius EG, of the angle mEG, & Gl, is also a tangent to the same Radius. of the Angle lEG. and Ce, Cf are similar tangents to the Radius EC (by construction)

Therefore lm. is the different of the tangents Gl. & Gm. so also ef is the difference of similar Tangents Cf. Ce.

Consequently no other projections but that of ef, can be the true representation of the diameter of the column I.

We prove in the same manner, dc, to be the true representation of the Column. H.

Hence it plainly appears that if the Tangents of the Aparent angles GEl, GEm, be set off upon the picture, to the radius EC, from C to l, & m. that fe, the difference of the tangent will be truly projected; for it fe, be shortned at discretion upon the picture, it will appear