156 



SCIENTIFIC NENA/S. 



[Sept. 1st, i8 



idea of a telephone, and it was embodied in Reis's instru- 

 ments as early as 1861, and a Frenchman named Bourseul 

 in 1854 had the same notion, but went farther than 

 vaguely hinting at it. The idea is derived from the Morse 

 telegraph apparatus, which in its simplest form, that of the 

 " single current sounder," consists of a galvanic battery, a 

 key arranged to make or break the circuit of the battery, 

 and an electro-magnet placed in that circuit and arranged 

 to attract an iron amature, whenever excited by the current 

 from the battery. Part of the circuit consists of the line 

 wire. The battery and key are at one end of the line, and 

 the electro-magnet (which, with its armature and necessary 

 fittings, is called the " sounder ") at the other. The circuit 

 is completed through the earth. In any electric circuit a 

 current can only flow when the circuit is complete, that is, 

 when the conducting line from one pole of the battery to 

 the other is complete. The " key " gives the means of 

 completing or breaking the telegraph circuit, and in its 

 normal position the circuit is not complete. When the key 

 is pressed down the circuit is closed, a current flows through 

 it, including of course the sounder, the armature is attracted 

 and kept down as long as the key "makes contact" or 

 closes the circuit. The sending telegraphist is thus able to 

 send a succession of currents of various lengths, and to rap 

 out on the sounder " dots " and " dashes " which spell out 



Fig. 4. Morse Sounder Circuit. 



letters and words in the telegraphic alphabet. Figure 4 is 

 a diagram of a Morse Sounder Circuit as described. K is 

 the key, shown in its normal position, the spiral spring 

 holding it in the breaking contact position, L is the line wire, 

 B the battery, and S the sounder, with the armature held 

 away from the electro-magnet by the opposing spring. In 

 practice, there is a key, battery, and sounder at each end of 

 the line, and the back contact which the key lever rests on 

 is connected to the sounder, so that there is always an un- 

 broken circuit, but without a battery to produce a current 

 in it, until either key is depressed, when the sounder at that 

 end is thrown out, and the battery thrown into circuit. 



If we make the key, K, very light and attach it to the 

 centre of a diaphragm like that of a Bell telephone, then it 

 can be easily seen that sound vibrations striking the dia- 

 phragm with sufficient force will complete the circuit at a 

 rate corresponding to the number of vibrations character- 

 istic of the sound. This number of short currents will flow 

 through the circuit, and each magnetising the electro magnet 

 of the sounder will set up a vibration in the armature 

 which will produce a musical note of the same pitch as the 

 one actuating the key. It will be readily understood that 

 the key, or, as we may now call the combined key and dia- 

 phragm, the transmitter, must be so adjusted that with 



normal air-pressure on the diaphragm the circuit is broken, 

 and with certain higher pressure the circuit is closed, then 

 every time the pressure due to a sound wave rises above 

 that point contact will be made, and every time the pressure 

 falls below it contact will be broken. If, then, a complex 

 sound wave acts on the diaphragm, the current cannot 

 correspond to its complexities, only the crests and hollows 

 of the wave, so to speak, will be represented, and the 

 wavelets which give to sounds their various characters cannot 

 be transmitted by an instrument which makes and breaks 

 contact, though for simple musical sounds the instrument 

 may transmit fairly well. The receiver, to give audible 

 sounds, should be arranged so that the vibrations may be 

 imparted to a fairly large surface, and the best receiver is 

 the Bell in one of its many varieties. 



It will be seen that any battery power, and therefore 

 any current strength that will not injure the apparatus 

 can be employed, and that therefore the receiver can give 

 out much more audible sounds than if actuated by the 

 feeble current from a Bell transmitter. 



So far, however, we have only got a transmitter for 

 comparatively simple sounds, and one that will not trans- 

 mit the delicate gradations of current representing the 

 ripples and wavelets of articulate speech. It is like an 

 engine throttle valve, which can only be at the " shut off" 

 or " full open " position. The driver with such a valve 

 could only stop or go at full speed. It is evidently 

 necessary to have a transmitter that will do more than 

 make and break the circuit, it must be capable of making 

 a more or less complete contact, or, as an electrician 

 would put it, must introduce more or less " resistance " 

 into the circuit. This can easily be managed. It is found 

 that when an electrical circuit is made through the con- 

 tact of two conductors, the resistance offered by that con- 

 tact depends, other things being equal, upon the pressure 

 forcing them together. The greater that pressure, the 

 lower the resistance and the stronger the current flowing 

 across the contact. The exact reason for this is still a 

 matter of dispute among experts, probably a number of 

 actions are concerned, but it is easy to understand that the 

 number of points actually in contact, and therefore the 

 number of roads open to the current, must correspond to a 

 certain extent with the pressure between the two surfaces. 

 This action is probably the most important one concerned. 



To enable a diaphragm, when spoken to, to communicate 

 all the gradations of pressure on it to a pair of contacts, both 

 contacts should be elastically mounted. 



Philipp Reis saw this, and in his first transmitters acted 

 on the principle. He took the human ear as his model, 

 holding the opinion that as the outer ear certainly received 

 all audible sounds, and transmitted them to the nervous 

 system of the inner ear, the mechanical arrangements of the 

 ear formed a good model for an electrical ear. In the ear we 

 find a diaphragm (a) (the tympanic membrane) at the end of 

 a tube (b); connected with the centre of the diaphragm (a) is 

 a little bone (c), forming one of a chain of three, the other end 

 of which is connected with a membrane (d) stretched across 

 the opening of a canal (forming one of a system of canals in 

 the bone of the skull), filled with a thin liquid, which 

 bathes the nervous arrangements. The whole of this is 

 shown diagrammatically in Fig. 5, and it will be seen that 

 the transmission mechanism is all elastic, but cannot come 

 apart, or " break contact." 



Reis followed this plan in his transmitters by making 

 the contacts springy or mounting them on springs, by which 

 means, as the diaphragm moved inwards under pressure, 

 while it encountered no rigid resistance to its motion, the 

 pressure between the contacts increased or diminished in a 

 way which bore a definite relation to its position at any 



