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RIGHT LINES IN WORKS OF ART.

or be inclosed by some resisting boundaries ; as, for exam-ple, wine in bottles, the water in rivers, in lakes, in thesea, &c.

Geometry supposes that bodies are solids; or at leastthat their form is not subject to change, except, accordingto some rule and within some limit, at the moment theybecome the object of investigation.

The most simple of all lines, and that which is the mostfrequently employed in the arts, is the right line.

A right line is the shortest distance between any twopoints : or that which we trace by always proceeding in thesame direction.

As there are not between any two points, two directions,of which, each may be shorter than the other, so there can-not be drawn two distinct right lines between any twopoints. When two right lines terminate in the same twopoints, they form, consequently, only one right line. Iftwo such lines are drawn on different bodies, and the twobodies are brought together, so that any two points of oneline coincide with any two points of the other line, thetwo lines adapt themselves in every point as if they formedonly one line. Of this property of right lines much use ismade in the arts.

1st. To ascertain that a line , already drawn , is a rightline, by means of another line , which is known to be a per-fect right line :—It is only necessary, in fact, to apply thelatter at any two points to the former, and see if all theother points of both correspond. If they do not, the lineexamined is not a right line, and it may be made so, orrectified, by the help of the perfect line.

2d. To trace right lines: —This is done by using bodiesnaving one or more rectilinear edges, such as common ru-lers or squares. The ruler or square is laid on a surface, towhich the right line, represented by the instrument, appliesexactly at every point; and unless it do so, it is not possibleto trace a right line on the surface. With a pencil, or anypointed or cutting instrument, a line is then drawn, which