_System by MM. Bréguet and Roosevelt._--In the system established by the Paris agents of the Bell company, the arrangement resembles the one just described, except that there is only one spring commutator, and the call is made with the push of an ordinary electric bell. A mahogany board is suspended from the wall, and on it are arranged, first, the ordinary electric bell system, with a sending push fixed below it; second, two forks supporting two telephones, one of which is fastened to the bar of a commutator, arranged as a Morse key. The two telephones are connected by two conducting wires, so arranged as to be capable of extension, and two of their four binding screws are in immediate connection with each other, and the other two with the earth, line, and battery, by means of the commutator, the sending push, and the bell system. The arrangement is shown in fig. 54. [Illustration: FIG. 54.] The commutator A consists of a metallic bar _a c_, bearing the suspension fork of one of the telephones F′ below its point of articulation: it ends in two pins _a_ and _c_, below which the two contacts of the commutator are fixed, and a spring compresses the lower arm of the bar, so as to cause the other arm to rest constantly on the higher contact. For greater security a steel tongue _a b_ is fastened to the lower end of the bar, and rubs against the small shaft _b_, which is provided with two insulated contacts, corresponding to those of the board. The bar is in communication with the line wire by means of the call-push, and the upper of the two contacts we have just described corresponds with one of the telephone wires which is inserted in the same circuit, while the other corresponds with the bell system S, which is in communication with earth. It follows from this arrangement, that when the right telephone presses its whole weight on the support, the bar of the commutator is inclined on the lower contact, and consequently the line is in direct communication with the bell, so that the call can be made. When, on the other hand, the telephone is removed from its support, the bar rests on the higher contact, and the telephones are connected with the line. Pressure on the sending push serves to call the corresponding station: the connection of the line with the telephones is then broken, and it is established with the battery of the sending station, which sends its current through the bell of the corresponding station. In order to obtain this double effect, the contact spring of the sending push generally rests upon a contact fastened to a piece of wood shaped like a joiner’s rule, which covers it in front, and below this spring there is a second contact, which communicates with the positive pole of the station battery. The other contact corresponds with the line wire, and a connection takes place between the earth wire and the negative pole of the station battery, so that the earth wire is common to three circuits: