Sept. 1st, 1887.] 



SCIENTIFIC NEVS^S. 



157 



Fig. 5. Tympanic Membrane of Human Ear. 



moment, and therefore the electrical resistance of the con- 

 tacts varied with the variations of air-pressure due to the 

 sound waves. It is interesting to know that Reis copied 

 very closely the actual form of the human ear in his first 

 transmitters, even carving the mouthpieces into rough 

 copies of the external ear. 



The transmitter shown in Fig. 6 is chosen for its clear 

 representation of the various essential parts of Reis's trans- 

 mitters. It was neither the earliest nor the latest of the 

 many patterns he made, but has the characteristic features 

 of all his designs. 



Fig. 6. The Hollow-cube Transmitter. 



Figure 6 shows a sectional view of the " hollow cube" 

 form of transmitter. The rectangular wooden block (a) has 

 a conical hole (b) bored through it from end to end, forming 

 the mouthpiece. Across the smaller end of this hole is 

 tightly stretched a diaphragm made of the intestine of a pig 

 (probably a piece of sausage skin), and marked c in the 

 figure. Two brass terminals, or binding screws, are fixed 

 into the block at d and c, and two strips of thin springy 

 brass start from each terminal and meet outside the centre 

 of the diaphragm at /. The one from the upper terminal 

 rests lightly upon the diaphragm, and carries a little button 

 of platinum. The strip from the lower terminal carries a 

 little spike of platinum resting on the platinum button, thus 

 forming a spring contact, the pressure on which is under 

 the control of the diaphragm. The lower brass strip has a 

 screw (h) passing through, and this serves to adjust its 

 tension. To the terminals d and e wires are attached, 

 putting the instrument in circuit with a battery and a tele- 

 phone receiver. When the diaphragm is put into vibration 



by sound waves, it will vary the pressure between the 

 contact point in a way corresponding to the pressure acting 

 on it, and if the tension of the strips is well adjusted to the 

 loudness of the sound, the contact will not be broken, their 

 springiness allowing them to follow the diaphragm in its 

 excursions. As already explained, the current in the circuit 

 will vary with the varying pressures on the contacts, and 

 the sound waves will be reproduced in the receiver, which 

 may be a Bell telephone, or one of Reis's own designs. 

 The principal features in which Reis's transmitter resembles 

 those most used at present are — i, The employment of 

 a diaphragm to gather the sound waves, and concentrate 

 them upon the "loose contact" ; 2, Mounting the contacts 

 on springs, so that they may follow the vibrations of the 

 diaphragm without breaking contact. The chief feature of 

 difference is in the use of metallic contacts, most trans- 

 mitters in commercial use employing carbon contacts. It 

 has been found, however, that some metallic contacts act 

 very well, the chief objections to them being their liability 

 to fusion, and oxidation, and the extremely fine adjustment 

 necessary, owing probably to the small compressibility of 

 the small points forming the surfaces. Reis used the 

 most infusible metal, one which does not oxidise when an 

 electric spark passes between the two points, and is 

 therefore one of the best metals that can be used. The in- 

 fusibility of carbon and its higher specific resistance, 

 enabling a larger surface of contact to be used, with a more 

 gradual variation of contact resistance, and less necessity 

 for extremely delicate adjustment, are the advantages which 

 have determined the all but universal use of carbon con- 

 tacts for variable resistance transmitters. 



With regard to the second point Reis always speaks of 

 " making and breaking" the circuit in a way corresponding 

 to the sound waves, and it has been argued that he had no 

 idea of the necessity for avoiding complete breaks, and 

 making the current strength vary in a wavelike or undulating 

 manner. The construction of his instrument, his written 

 explanations and diagrams of sound waves, scarcely bear 

 out this contention, and as there is no doubt that his instru- 

 ments transmitted and received speech (perhaps not very 

 perfectly), Reis must in fairness be credited with the inven- 

 tion of the speaking telephone. We must just look for a 

 few moments at Reis's receiver, as it is original and ingeni- 

 ous in conception, though superseded by the Bell now. 



In 1837 Page discovered that an electro-magnet gave out 

 a click whenever the magnetising current was either started 

 or stopped ; and it was found on investigation that the 

 iron of an electro-magnet was lengthened to a very slight 

 extent upon magnetisation, and attained its original length 

 on the stoppage of the mangetising current. The change 

 of length is no doubt the cause of the click. Reis took 

 advantage of this effect. His receiver shown in Figs. 7 and 

 8 consisted of a coil of insulated wire a, a thin wire of iron 

 or steel, forming the core of the electro-magnet l>, resting 

 on wooden supports something like two violin bridges, glued 

 to the top of a shallow box made of thin wood. This box 

 strengthens the vibrations of the iron in the same way as 

 the body of a violin reinforces the string vibrations. In 

 fact Reis in his earliest instruments used a violin body, 

 first sticking one end of the iron wire into one of they holes 

 of the violin, and afterwards attaching one end to the bridge 

 of the violin. The way in which this instrument converts 

 En undulatory current into sound waves is obvious, the 

 lengthening and shortening of the iron throwing the 

 box into vibration, so that in this instrument the flat top 

 of the box played the part of the diaphragm in the Bell 

 receiver. It is a litile curious that Reis should never 

 have tried a diaphragm in his receivers, but such seems to 

 have been the case. The only form of receiver he seems 



