Cylinder

(sil'in-dur.) [From Gr. kylindro, I roll.] (Geom.) A solid body, supposed to be generated by the rotation of a parallelogram round one of its sides. This will produce a solid, shaped like a column with parallel sides. If a line from the centre of the upper surface, let fall perpendicularly on the lower, touches the centre of the latter, it is a right C.; otherwise it is oblique. The solid contents of a C., whether right or oblique, is found by multiplying the area of the base by its altitude, and its convex surface is found by multiplying the circumference by the height. The area of the internal diameter ofa C., multiplied by its depth, will give the cubical capacity. The solidities of a cone, of a sphere, and of a C., formed by the revolution of a square on a line pa ing through and bisecting it-the circumferences of the bases of the cone and C. and the great circle of the sphere being equal-are as 1, 2, and 3. This ratio was first discovered by Arch i me des. (Mach.) In steam-engines, that part in which the piston works to and fro, and from which, by alternately admitting and condensing the steam, all the motive power of the engine is derived.-(Agric.) A roller used in flattening the surface of ploughed ground. [s. 258]