One very curious point in connection with this “knitting-needle” receiver of Reis, is its extremely bad acoustical arrangements. It was laid horizontally upon a small sounding-box covered by a lid. If the _end_ of the needle had been made to press on the resonant-board (as indeed appears to have been done at first with the violin, p. 29) the vibrations would have been much more directly reinforced. But when merely supported by two wooden bridges the direct communication was largely lost. The pressure of the lid downwards upon the spiral, as recommended by Reis, is no doubt an important matter acoustically. It is strange that a man who had grappled in so masterly a way with the acoustical problem of the transmitter, and had solved it by constructing that transmitter on the lines of the human ear, should not have followed out to the same extent those very same principles in the construction of his receiver. An extended surface he did employ, in the shape of a sounding-board; but it was not applied in the very best manner in this instrument. The second principle applied by Reis in the construction of his telephone-receivers, was that of the electro-magnet. He arranged an electro-magnet so that the fluctuating currents passing round the coils set up corresponding variations in the degree of force with which it attracted its armature of iron, and so forced the latter to execute corresponding mechanical vibrations. This principle is common both to the receiver of Reis, and to the later receivers of Yeates, Bell, and Edison. Reis’s armature was an iron bar of oval section; Yeates’s an iron strip screwed to a sound-board, Bell’s was an iron plate, and Edison’s an iron plate also.