“Figure 348[33] exhibits Reis’s interrupting apparatus. In the lid of a hollow cube of wood A, a circular opening is made, which is closed by an elastic membrane (pig’s lesser intestine) strained over it. Upon the centre of this membrane is glued a little plate of platinum, which stands in conductive communication with the clamping-screw _a_ by means of a quite thin little strip of metal _f_ (distinctly visible in Fig. 349) [Fig. 31]. “Upon the middle of the little platinum plate, rests a short little platinum pencil, which is fastened at _g_ to the under-side of the strip of tin-plate _h g i_, one end of which, _h_, rests upon the little metal pillar _l_, while a little platinum spike fastened upon its under-side at _i_, dips into the hollow of the little metal pillar _k_, containing some quicksilver. The clamping-screw _b_, is put into conductive communication with the little metal pillar _k_. “From one pole of the battery there goes a conducting-wire to the clamping-screw _a_ of the interrupting apparatus Fig. 348 [Fig. 30], from the other pole of the same there goes a wire to the clamping-screw _d_ of the reproducing apparatus, Fig. 350 [Fig. 32], which is to be presently described. The clamping-screw _c_, of this apparatus, is connected by a wire with _b_, Fig. 348 [Fig. 30]. The clamping-screws _c_ and _d_ are connected with the ends of the wire of the small magnetising spiral M, Fig. 350 [Fig. 32]; with the connexion described above, the current of the current-generator (battery) goes, therefore, through the spiral M. “As soon now as the sound-waves of an adequately powerful tone enter through the mouth-piece S into the hollow cube A, the elastic membrane which closes this at the top is set into vibrations. Each wave of condensation on entering lifts the little platinum plate together with the little spike which sits upon it; but if the membrane swings downwards, the tin-piece _h g i_, with the little spike at _i_, cannot follow it quick enough; there therefore occurs here, at each vibration of the membrane, an interruption of the current which lets itself be recognised by a little spark appearing at the place of interruption. [Illustration: Fig. 30.] [Illustration: Fig. 31.] [Illustration: Fig. 32.] “Now in the spiral M is stuck a knitting-needle, which, as the figure shows, is fastened into a sounding-board. A lid provided with second sounding-board may be clapped over the spiral, and the tone be thereby greatly strengthened. “If now, tones are produced before the mouth-piece S, whilst one sings into the same or whilst one blows organ-pipes, one at once hears at the reproducing apparatus a peculiar creaking noise which is independent of the pitch of the tones produced at the interrupting apparatus, _but, beside this, those tones are themselves reproduced by the steel wire distinctly perceptibly_, and indeed Reis found that this is the case for all tones between F and _f''_.