ROLE, Use of the Carpenter's Joint. The application of the inches in measuring lengths, breadths, &c., is obvious. That of the Gunte•'s line, see under Gunter's Lines, in the article INSTRUMENTS. The use of the other side is all we need here illustrate. .

I. The breadth of any surface, as board, glass, cf•e. being given; to find how muck in length will make a square Find the ntunber of inches the surface is broad, in the line of board-measure ; and right against it, on the inches side, is the number of inches required. Thus, if the surface were S inches broad, IS inches will be found to make a superficial foot.

Or, more readily, thus : Apply to the breadth of the board or glass, that end of the rule marked 36, laying it even with the edge ; the other edge of the surface will show the inches and quarters of inches which go to a square foot.

To find the content of a given surface : Find the breadth and how much makes one foot ; then turn .that over as many times as you can upon the length of the surfitce,and so many feet does the surface contain.

2. Use of the table at the end of the board-measure.—If surface be one inch broad, how many inches long will make a superficial foot ? Look in the upper row of figures for • 1 inch, and under it, in the second row, is 12 inches, the answer to the question.

3. Use of the line of timber-measure.—This resembles the former ; for, having learned how much the piece is square, look for that number on the line of timber-measure ; the space thence, to the end of the rule, is the length, which, at that breadth, makes a foot of timber. Thus, if the piece be inches square, the length necessary to make a solid foot of timber is 2.11 inches. If the timber be small, and under 9 inches square, seek the square in the upper rank of the table, and immediately under it are the feet and inches that make a solid toot. Thus, if it be 7 inches square, 2 feet 11 inches will be found to tnalce a solid foot.

If the piece be not exactly square, but broader at one end than the other, the method is, to add the two together, and take half the sum for the side of the square. For round timber, the method is, to girt it round with a string, and to allow the fourth part for the side of the square. But this method is erroneous; for hereby above a fifth of the true solidity is lost. See SLIDING RULE, and TIMBER.