_Secondly_, that Reis intended such interruptions or variations of contact to be proportional to, or to “correspond” with, the variations indicated by the undulatory curve of varying pressures. _Thirdly_, that for the purpose of preventing the occurrence of abrupt breaks in the continuity of the circuit, he used springs and adjusting screws, and in one form availed himself of the inertia of the moving parts to attain a similar end. It is also clear from his own prospectus, that he was aware that for the simpler and ruder purpose of transmitting musical airs, in which the number of the vibrations is the only consideration and where each single condensation is actually followed by a rarefaction, actual abrupt breaks in the continuity of the circuit are admissible. Reis chose this simple case as the one capable of being readily grasped by a general audience, though it was obviously only a partial explanation of the action of the apparatus in the simplest case that could be presented. * * * * * Turning now to some of the more modern transmitters, we will inquire how far Reis’s fundamental principles are involved in their construction. We will first take Berliner’s transmitter, of which Fig. 43 is a drawing, reproduced from the sketch in the specification of his British Patent. This transmitter consists of a tympanum of thin metal to collect the sound-waves, and behind it is attached an interrupter or current regulator, identical in almost every respect with that of Reis. One of the contact-pieces, marked _E_, circular in form, is fixed to the centre of the tympanum, and vibrates with it, precisely as in Reis’s latest, and in some also of his earlier instruments. Against this there rests in light contact a second contact-piece, in the form of a small blunt spike, _F_, screwed into a short arm, loosely jointed to the part _N_, where the circuit is connected. As in Reis’s latest transmitter (Fig. 17, p. 27), so here, the contact-pieces are kept in contact by gravity. When any person talks to the tympanum it vibrates, and, as a result, the degree of contact between the two surfaces is varied, resulting in a greater or less interruption of the current, the inertia of the upper contact-piece, serving to prevent complete abrupt “break” of the circuit, except under unusually strong vibrations. In fact, if the speaker talks too loudly when speaking into Berliner’s transmitter, he will cause abrupt breaks to occur instead of partial interruptions; and a rattling noise comes in to confuse the speech at the receiving end of the line. But this is precisely what occurs in a Reis’s transmitter if one talks too loudly to it. It is obvious that if Berliner’s transmitter is a “make-and-break” instrument, so is Reis’s, because the principle of action is identical: and it is also obvious that if Berliner’s instrument is capable of varying the resistance at the contact-points by interrupting the current in a