“In a cube of wood, _r s t u v w x_, there is a conical hole _a_, closed at one side by the membrane _b_ (made of the lesser intestine of the pig), upon the middle of which a little strip of platinum is cemented as a conductor [or electrode]. This is united with the binding screw _p_. From the binding screw _n_ there passes likewise a thin strip of metal over the middle of the membrane, and terminates here in a little platinum wire, which stands at right-angles to the length and breadth of the strip. From the binding-screw _p_ a conducting wire leads through the battery to a distant station.” The identical apparatus used by Reis was afterwards given by him to Professor Böttger, who later gave it to Hofrath Dr. Th. Stein, of Frankfort, from whose hands it has recently passed into the possession of the author of this work. It possesses one feature not shown in the original cut, viz. an adjusting screw, _h_, which, so far as the writer can learn, was put there by Reis himself. There appears no reason to doubt this, since there was an adjusting screw in Reis’s very earliest form of transmitter, the wooden ear. A section of the actual instrument is given in Fig. 10. [Illustration: Fig. 10.] _Fifth Form._--THE HOLLOW CUBE. Another form, a mere variety of the preceding, is described as follows by Professor Böttger in his “Polytechnisches Notizblatt” (see p. 61):-- “A little light box, a sort of hollow cube of wood, has a large opening at its front side and a small one at the back of the opposite side. The latter is closed with a very fine membrane (of pig’s smaller intestine) which is strained stiff. A narrow springy strip of platinum foil, fixed at its outer part to the wood, touches the membrane at its middle; a second platinum strip is fastened by one of its ends to the wood at another spot, and bears at its other end a fine horizontal spike, which touches the other little platinum strip where it lies upon the membrane.” _Sixth Form._--THE WOODEN CONE. [Illustration: Fig. 11.] Another transmitter, also a mere variety of the Fourth Form, has been described to me by Herr Peter, of Friedrichsdorf, who assisted Reis in his earlier experiments. Fig. 11 is prepared from a rough sketch furnished me by the kindness of Karl Reis. Herr Peter describes the apparatus as having been turned out of a block of wood by Reis upon his own lathe. The conical hole was identical with that of Fig. 9, but the surrounding portions of the wood were cut away, leaving a conical mouth-piece. _Seventh Form._--“HOCHSTIFT” FORM. [Illustration: Fig. 12.]