Fig. 2 is a plan of the receiving instrument, in which h h are the light pivoted needles surrounded by coils of fine insulated copper wires, i i, and controlled in their zero position by the electro-magnets, j j j j, placed underneath, the whole forming a pair of galvanoscopes or current detecters, one for each line. It will be understood that the varying currents from the lines are allowed to flow through the coils, i i, so as to deflect the needles, and that the deflections of the needles follow, so to speak, the variations of the currents. The electro-magnets are magnetized by a local battery; permanent magnets might, however, take their place with a gain in simplicity. Now the writing pen, k, is connected to the nearest tip of the needle, h, of each galvanoscope by threads, n n, which are kept taut by the fibers, o_{1} o_{2} o_{3}, the springs, o, and the pins, o_{4}. In this way the motions of the needles are recombined in the motion of the duplicate pen upon the paper, p. Fig. 1 is an elevation of the receiving instrument, in which i i are the coils as before, j j j j the controlling electro-magnets, k is the writing siphon dipping with its short leg into the ink well, m, and l is the bridge from which the writing siphon is suspended by means of a thread and spring. The long leg of the siphon reaches down to the surface of the paper, p, which is pulled along beneath it in contact with the film of ink filling the point of the tube. When the siphon is at rest its point marks a zero line along the middle of the paper, but when the receiver is working, the siphon point forms each letter of the message upon the paper as it passes.--_Engineering._ * * * * * ALUMINUM. The splendid exhibit of the French aluminum manufacturers at the late Exhibition has again called attention to that metal, which is so admirably adapted to many purposes on account of its great lightness and its stability under the influence of the atmosphere. While aluminum industry has heretofore been thought to be confined to France solely, we are now told by Mr. C. Bambery, in the Annual Report of the Society of Berlin Instrument Makers, that for some years past aluminum has been extensively manufactured in Berlin. Three firms especially (Stueckradt, Haecke, and Schultze) are engaged in this branch of industry. The articles manufactured principally are nautical instruments, as sextants, compasses, etc. The German navy is supplied throughout with aluminum instruments. As a proof of the superiority of German aluminum, it may here be mentioned that the normal sets of weights and balances used by the International Commission for the regulation of weights and measures, which lately was in session at Paris, were obtained from Stueckradt, in Berlin, and not from any of the firms at Paris, the reputed seat of aluminum industry.