The applications of the telephone are much more numerous than might be supposed at the first glance. As far as the telegraphic service is concerned, its use must evidently be rather limited, since it cannot register the messages sent, and the speed of transmission is inferior to that of the improved system of telegraphs; yet in many cases it would be very valuable, even for a telegraphic system, since it is possible to work it without any special telegraphic training. The first comer may send and receive with the telephone, and this is certainly not the case even with the simplest forms of telegraphic instruments. This system is therefore already in use in public offices and factories, for communication in mines, for submarine works, for the navy, especially when several vessels manœuvre in the same waters, some towed by others; finally, for military purposes, either to transmit orders to different corps, or to communicate with schools of artillery and rifle practice. In America the municipal telegraphic service and that of telegraphs limited to the area of towns are conducted in this way, and it is probable that this system will soon be adopted in Europe. Indeed, a service of this kind was established in Germany last autumn at the telegraph offices of some towns, and the London Post Office is now thinking of establishing it in England. But, besides its use for the purposes of correspondence, the telephone can be useful to the telegraphic service itself by affording one of the simplest means of obtaining a number of simultaneous transmissions through the same wire, and even of being combined in duplex with the Morse telegraphs. Its applications in the microphonic form are incalculable, and the proverb which declares that ‘walls have ears’ may in this way be literally true. It is alarming to think of the consequences of such an indiscreet organ. Diplomatists must certainly redouble their reserve, and tender confidences will no longer be made with the same frankness. On this point we cannot think that much will be gained, but on the other hand the physician will probably soon make use of this invention to ascertain more readily the processes going on within the human body. APPLICATION OF THE TELEPHONE TO SIMULTANEOUS TELEGRAPHIC TRANSMISSIONS. The simultaneous transmission of several messages through the same wire is one of the most curious and important applications of the telephone to telegraphic instruments which can be made, and we have seen that it was this application which led Messrs. Gray and Bell to the invention of speaking telephones. The admiration which these instruments have excited has thrown the original idea into the background, although it has perhaps a more practical importance. We will now consider these systems.