The speed of the machine, which is commonly from four to five thousand ems per hour, but which has reached ten thousand and upward in competitive trials, is due to the fact that the matrices pursue a circulatory course, leaving the magazine at the lower end, passing thence to the line and to the casting mechanism, and finally returning to the top of the magazine. This permits the composition of one line, the casting of another, and the distribution of a third to proceed simultaneously. ASSEMBLING AND KEYBOARD MECHANISMS The matrices pass through the magazine by gravity. Their release is effected by mechanisms shown in Figs. 5 and 6, which are vertical sections through the magazine, the keyboard, and intermediate connections. Under each channel of the magazine, there is an escapement _B_, consisting of a small lever rocking at its centre on a horizontal pivot, and carrying at its opposite ends two dogs or pawls _b, b_, which are projected up alternately into the magazine by the motion of the lever. The key-rod _C_, suspended from the rear end of the escapement _B_, tends to hold the lower pawl _b_ in an elevated position, as shown in Fig. 5, so that it engages under the upper ear of the foremost matrix to prevent its escape. [Illustration: Fig. 5.] When the escapement _B_ is rocked, it withdraws the lower pawl _b_, as shown in Fig. 6, at the same time raising the upper pawl, so that it engages and momentarily arrests the next matrix. As soon as the first matrix has escaped, the escapement resumes its original position, the upper pawl falling, while the lower one rises so as to hold the second matrix, which assumes the position previously occupied by the one released. [Illustration: Fig. 6.]