(138.)

It is sometimes required to put one tube or passage alternately in communication with two others. This is accomplished by a two-way cock. In this cock the passage is curved, opening usually at points on the surface of the cock, at right angles to each other. Such a cock has already been described, and its use illustrated in the description of the Marquis of Worcester's engine (17.); the two-way cock, as represented at K and R ( fig. 4.), being the means by which steam and water are alternately supplied to the two forcing vessels.

Figs. 59., 60.