Sept. 



la] 



NA TURE 



517 



very handy, pretty, and convenient form. He utilises a principle 

 which he calls " surrexcitation. " A thick ring of soft iron is 

 inserted between the earpiece and the diaphragm, and this is 

 said to increa-e the attractive power of the little horse-shoe 

 magnet upon the vibrating iron diaphragm. A simple experi- 

 mental apparatus of M. Adder's shows that there is some founda- 

 ton for this fact : when a thin steel -pring is adjusted close to 

 the poles of a magnet without being attracted by them, the 

 near approach of a mass of iron to the spring will can 

 attracted by the magnet 



D'Arsonval has also modified the Bell receiver. He has 

 placed the coil in a powerful magnetic field of annular form, and 

 has thereby concentrated the lines of force upon the induced coil. 

 lie brings the whole coil within the influence of the field. The 

 effects are said to \ic magnified, and the increased loudness is 

 not accompanied by the usual loss of articulation. Speech is 

 reproduced w ithout any change of timbre. 



Telephone receivers of the Bell type are all based upon the 

 magnetic effects of currents of electricity flowing around magnets 

 or bars of soft iron. 



The rapid and rhythmic magnetisation and demagnetisation of 

 a bar of iron or the increment and decrement of the magnetism 

 of a magnet, w ill produce molecular disturbances, in it own 

 mass and in the matter about it, that lead to the oscillatory 

 if the whole which produce sonorous vibrations that 

 can be made manifest by various devices, and particularly by 

 that patented by Graham Bell. 



Other principles of electricity have also been utilised for 

 telephonic receivers. 



tance, Mr. Edison used the electro-chemical effect. 

 The decomposition of a chemical solution in paper or on chalk 

 by the passage of currents through it, produces a modification 

 of the friction of two moving surfaces, which can reproduce 

 sonorous vibrations, and the result is a very loud-sounding 

 apparatus. I myself had the pleasure, in 1880, of submitting 

 to the koyal Society a receiver based on the electro-thermal 

 effects of the current. The passage of a current through wires 

 always heats them and therefore produces expansion. If the 

 wire be made fine enough, the heat is generated and dissipated 

 so rapidly, the expansion and contraction are so rjuick, that 

 sonorous vibrations are the result. Although I was able to 

 speak through it very clearly, I have not as yet developed this 

 instrument into a practical form. Pr o n ato r Oolbear has recently 

 utilised the electro-static effects of currents. His receiver is 

 even more simple than that of Bell. Two flat circular discs of 

 metal are rigidly fixed very close to each other in an insulated 

 case of ebonite. When one disc is electrified positively by a 

 charge of electricity, the other is electrified negatively by induc- 

 ite states produce attractions varying in 

 force with the strength of the signals sent, and the result is that, 

 when telephonic currents are transmitted, we obtain sonorous 

 vibrations, and, consequently, the reproduction of speech. 



Many other forms of telephone receivers have been devised 

 and exhibited, in fact I have recently seen quite a crop of them ; 

 but as they involve no new principle, and introduce no particular 

 improvement, having been brought out chiefly to try to avoid 

 existing patents, I pas them over, and proceed to the next 

 branch of my subject. 



Our present Patent Law Is, unfortunately, in so disorganised 

 and chaotic a condition, that evasion is often possible, and hence 

 the questionable morality of doing a thing in another way, in 

 order to avoid the incidence of a royalty, is practically encouraged. 

 The possession of a patent is now no guarantee of property : 

 it i.s granted without any discrimination, and cannot be upheld 

 without tedious litigation and wasteful expenditure before a non- 

 technical and scientifically incompetent tribunal. We therefore 

 cannot hope for any virtue in Englih inventors or security for 

 real improvements until our law is thoroughly revised. The 

 question is before the House of Commons, and, when wordy 

 agitators have fully exhausted the patience of our legislators, we 

 may hope for some attention to so real and pressing a want. 



Transmitters. — The great novelty and peculiarity of Bell's 

 telephone was that the receiver and transmitter were similar and 

 reversible. Sonorous vibrations of air impinging on an iron 

 di«c cau-ed it to vibrate in front of a magnet around one pole of 

 which a portion of an electric circuit was wound. These 

 vibrations of a magnetic substance in a magnetic field produced 

 current- of electricity in the coil of wire on the magnet, varying 

 in strength and direction with the sonorous vibrations, which, 

 proceeding along a wire to a distant station, there varied the 



magnetic strength of a similar magnet so as to vary its 

 attractive force on a similar disc, by which it reproduced the 

 I the first die, and thu-, reproducing the sonorous 

 vibrations of the air, repeated speech. The currents, however, 

 were very feeble ; much energy was lot en route, and the effeel 

 scarcely attained a practical standard. Mr. Edison showed how 

 to strengthen these currents. Taking advantage of a i<culiar 

 property of carbon which was supposed to vary in electrical 

 resistance with the amount of pressure brought to bear upon it, 

 he cau-ed the vibrating die which was spoken against to press 

 upon a button of carbon, and so to vary the strength of a current 

 of electricity passing through it. This varying current, 

 through the primary wire of an induction coil, set up in the 

 secondary rful currents than the Hell instrument 



produced, and caused louder and more marked effects at the 

 receiving station. Professor Hughes went a step further. He 

 found a combination of materials that v;at directly affected by 

 sonorous vibrations, which he called a "microphone," and he 

 proved that the effect of the carbon transmitter of Edison was 

 not due to any influence of varying prcs-urc on the mass of the 

 carbon, but was a phenomenon of loose contact. He found a 

 new fact in nature, and he startled the scientific world by intro- 

 ducing an instrument which did for minute sounds what the 

 microscope had already done for minute objects. By the light 

 thrown on the theory of the instrument by Hughes, Edison's 

 carbon transmitter has been so improved by Blake, Hunn.ngs, 

 Moseley, Anders, and others, that little apparently remains to 

 be done. The telephone as a speaking instrument is now well 

 nigh perfect. It is quite possible to swear to a friend's voice at 

 too miles distance. The difficulty of making the telephone a 

 practical instrument under all circumstances is not due to any 

 defects in the instrument itself, but 1 influences 



external to it, and consequent on its surroundings. The very 

 Defection and sensitiveness of the apparatus it-elf are it, chief 

 enemies. 



The true action of the microphone, or carbon-transmitter, is 

 very little understood : it introduces into a closed electric 

 circuit, through which a current is flowing, a rc-i-tancc which, 

 varying exactly with the sonorous vibrations impinging 11; on it, 

 cau-cs the current to undulate in a way exactly analog" 



mind waves. This effect is generally as-umed to be 

 due to a greater or less intimacy of electrical contact between 

 two semi-conducting surfaces abutting upon each other ; but 

 there is now little doubt that it is due to effects of heat generated 

 by the passage of electricity between two points in imperfect 

 contact, whose relative distance is variable. Carbon is the best 

 material for the purpose — first, because it i 



y, because it is a poor conductor; and, thirdly, 

 becau-e it has the remarable property of having its n 

 lowered when it is heated — the reverse of metals. This obser- 

 vation is due to Mr. Shelford Bidwell. 



The resistance of microphones is very variable : some give 

 10", while others give 25", and some even 125". The best 

 transmitters that I have worked with (Moseley 's) give an 

 average of 20". 



Attempts have been made to apply mathematical analysis to 

 the determination of the best form and arrangement of micro- 

 phone , but at present the microphone defies mathematics. 



Theory would lead to the conclusion that a carbon-transmitter 

 should have the lowest possible resistance, but practice does not 

 confirm that idea. 



Theory again asserts that the resistance of the secondary coil 

 of the induction coil should be equal to that of the line it works, 

 but practice proves the very reverse. On a line giving nearly 

 tance, the best effects w ere produced with a secondary 

 wire of only 30" resistance. The fact i, that the conditions 

 due to heat in the microphone, and to self-induction in the 

 induction coil, are very complicated, and are not yet sufficiently 

 d to bring the phenomena they affect within the region 

 of mathematical anal;. 



Accessories. — I do not intend to speak here of the bells, call-, 

 switches, etc., used in carrying out telephonic operations : there 

 has been nothing that is particularly novel introduced, or that 

 was not previously used in telegraphy. In fact, the whole 

 operations carried on in connection with the so-called " exchange" 

 working are simply telegraphic, and are still in a somewhat 

 tentative con'ir i 



Longdistance Speaking. — I have said that the difficulty in 

 speaking i-> chiefly due to the environment of the w ires employed. 

 Were we to erect a wire from Land's End to John o' Groats, 



