We illustrate in the annexed engraving the microphone-telephone constructed by Messrs. Mix & Genest, of Berlin, which, after extended trials, has been adopted in preference to others by the imperial postal department of Germany. There are now more than 5,000 of these instruments in use, and we need scarcely mention that the invention has been patented in many countries. In some microphones a rattling noise is frequently occasioned, which borne along with the sound of the human voice causes an audible disturbance in the telephone. The chief cause of these disturbances may be ascribed to the fact that the carbon rollers in their journals, rest loose in the flutings of the beam, which is fastened to the sound plate. Owing to the shocks given to the entire apparatus, and independent of the oscillations of the sound plate, they are set in motion and roll to and fro in their bearings. In microphones in which the sound plates are arranged vertically (as shown in Fig. 2), these disturbances assume such a character that there is no possibility of understanding the speaker, for in this case the horizontally directed oscillations of the sound plate, _m_, cause themselves a backward and forward motion on the part of the carbon rollers without increasing or decreasing at the same time the lying-on pressure of the roller journals, and by doing so bring the places of contact one on the other, and thus occasion a conducting resistance of greater or less force. This circumstance serves as an explanation of the reason why the sound plates in Ader's microphones are not arranged vertically, although this way of arranging them offers many advantages over a horizontal or slightly inclined arrangement of the sound plates. Speaking is more convenient in the vertical arrangement, and moreover the plates can be fitted on to instruments better in this way. All the drawbacks just enumerated and found in Ader's microphones are avoided in the apparatus made by Messrs. Mix & Genest. A sort of braking contrivance operates on the carbon rollers in such a way as to prevent their journals from lying on the lower points in the flutings of the beams. Thus, for instance, if in a microphone with a horizontal sound plate, as illustrated in Fig. 3, the carbon rollers are pressed upward by outward force, it is evident that only a very trifling rolling and disturbing motion can occur, and only small pieces of carbon can be knocked off, which would act injuriously as a secondary contact. The same may be said of the journals of microphones with vertical sound plates, as represented in Fig. 2, when the carbon rollers are pressed in the direction of the arrow, _p_, that is to say, against the sound plate. In this case the journals, _a_, are fixed in the flutings of the beams, _b_, in a direction given them by the power and gravity operating on them, which is clearly represented in the accompanying design, Fig. 2.