. Pratica telefonica americana. Ver stesso essendo montato sull'opposto. La leva, L, in corrispondenza di ciascuna stazione, mostrata schematicamente in Fig. *** 525, è atta a scorrere sui pulsanti 1, 2, 3 e 4, come nei sistemi già descritti. Il pezzo di contatto curvo, D, è disposto in modo tale che la leva non si impegna normalmente, ma per pressione sui SISTEMI DI INTERCOMUNICAZIONE. 741 maniglia della leva può essere portata in impegno con la leva di comando. Facendo nuovamente riferimento alla Fig. 524, H è l'interruttore a gancio atto a formare le funzioni ordinarie di collegamento dell'apparecchio di chiamata e conversazione alternativamente i

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. American telephone practice . ver itself being mounted on the oppositeside. The lever, L, at each station, shown in diagram in Fig, 525, is adapted to slide over the buttons, 1, 2, 3, and 4, as in the systemsalready described. The curved contact-piece, D, is so arranged thatthe lever will not normally engage it, but by pressure upon the INTERCOMMUNICATING SYSTEMS. 741 handle of the lever it may be brought into engagement with the con-tact. Referring again to Fig. 524, H is the hook-switch adapted to per-form the ordinary functions of connecting the calling and talk-ing apparatus alternately in the line circuit. The switch lever ismounted upon the shaft, A, which may be seen passing through thefront board of the box and which carries a ratchet-wheel, E, ofhardened steel. A coiled spring around the shaft tends to rotate itso as to bring the lever always to the home position. F is a slidingpawl normally held in its lower position by a coiled spring sur-rounding it. This sliding pawl serves to hold the lever, L, in any. FIG. 525.—CIRCUITS OF HOLTZER-CABOT SYSTEM. position to which it has been rotated, by the engagement with theteeth of the ratchet-wheel, E. Upon the short arm of the hook-switch is pivoted a dog, G, adapted, when the receiver is placed uponthe hook to engage a notch in the pawl, E, and lift it out of engage-ment with the ratchet-wheel. This allows the spiral spring to re-turn the switch lever to its right-hand position in contact with thehome button. After raising the pawl out of the notch on theratchet-wheel the dog slips out of the notch on the pawl, thus allow-ing the latter to return into contact with the ratchet-wheel, in orderto be ready for the next use of the telephone. In order, however, that the pawl may not engage the ratchet before the lever. A. has 42 AMERICAN TELEPHONE PRACTICE. fully returned to its normal position, a second dog, /, is provided, which is pressed by a spring so as to occupy a position under thepin, p, carried on the pawl,

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