year Marconi sailed for Buenos Ayres, and wireless communication with Clifden was maintained up to the almost incredible distance of 4000 miles by day, and 6735 miles by night. The Marconi system has had many formidable rivals, but it still holds the proud position of the most successful commercial wireless system in the world. We have not space to give a description of the other commercial systems, but a few words on some of the chief points in which they differ from the Marconi system may be of interest. We have seen that an ordinary spark gap, formed by two metal balls a short distance apart, becomes overheated by the rapid succession of discharges, with the result that the sparking is irregular. What actually happens is that the violent discharge tears off and vaporizes minute particles of the metal. This intensely heated vapour forms a conducting path which the current is able to cross, so that an arc is produced just in the same way as in the arc lamp. This arc is liable to be formed by each discharge, and it lasts long enough to prevent the sparks from following one another promptly. In the Marconi system this trouble is avoided by means of a rotating spark gap, but in the German “Telefunken” system, so named from Greek _tele_, far off, and German _Funke_, a spark, a fixed compound spark gap is used for the same purpose. This consists of a row of metal discs about 1/100 inch apart, and the spark leaps these tiny gaps one after the other. The discs are about 3 inches in diameter, and their effect is to conduct away quickly the heat of the discharge. By this means the formation of an arc is prevented, and the effect of each discharge is over immediately, the sparks being said to be “quenched.” The short discharges enable more energy to be radiated from the aerial into the ether, and very high rates of sparking are obtained, producing a high-pitched musical note. The “Lepel” system also uses a quenched spark. The gap consists of two metal discs clamped together and separated only by a sheet of paper. The paper has a hole through its centre, and through this hole the discharge takes place, the discs being kept cool by water in constant circulation. The discharge is much less noisy than in the Marconi and Telefunken systems, and the musical note produced is so sensitive that by varying the adjustments simple tunes can be played, and these can be heard quite distinctly in the telephone at the receiving stations.