The Universal British Builder.

203

EXAMPLE.

First draw a base line equal to the width of thearch you intend; from the middle raise a perpen-dicular equal to the height, and likewise continue' it below the base line ; then from the height to thepoint of half the width, draw an hypothenuse line,m the middle of which set to your square, and drawa line into the perpendicular, which will be thecenter required : and so of every other circle.

An eleptic may be struck with a trammel for arough arch ; but the most exact and best method isto divide half the width and the height into anynumber of equal parts, and draw intersectionof lines, which will form the arch desired.

The centers being done, the next thing that re-quires the carpenters thoughts, is, the plates forthe floors to rest upon in the walls, which are of thegreatest service imaginable, both with respect tostrength, and form in practice; also, if the build-ing is of no consequence, and requires binding-joists,consider well the nature of them, both with respectto scantling and disposition, and that they by nomeans exceed g feet 6 inches apart, or 4 feet at thefarthest, to prevent too great a scantling for thebridgings.

The practice of this work is familiar ; the bind-ing-] oists are mortised into the girder flush with theunder-side, and so much below the top as will allowthe thickness of the bridgings to be equal with thetop of the girder ; the binding-joist mortised nearthe under-edge, for the ceiling-joists at one end,and flip into a chafe-mortife at the other.

Partitions come next under our examination,but require no difficulty : the principal thing in

B b 2 par-