240 



NATURE 



\yune 27, 1878 



that both actions ocair, but the latter seems to me the ti-ue 

 explanation ; for if the first was alone true, we should have a far 

 greater effect from metal powder, carbon, or some elastic con- 

 ductor as metallised silk, than from gold or other hard unoxidi- 

 sable matter ; but as the best results as regards the human voice 

 were obtained from two surfaces of solid gold, I am inclined to 

 view with more favour the idea that an infinite change of fresh 

 contacts brought into play by the molecular pressure affords the 

 true explanation. It has the advantage of being supported by 

 the numerous forms of microphone I have constructed, in all of 

 which I can fully trace this effect. 



I have been very much struck by the great mechanical force 

 exerted by this uprising of the molecules under sonorous vibra- 

 tions. With vibrations from a musical box two feet in length 

 I found that one ounce of lead was not sufficient on a surface of 

 contact one centim. square to maintain constant contact ; and 

 it was only by removing the musical box to a distance of 

 several feet that I was enabled to preserve continuity of 

 current with a moderate pressure. I have spoken to forty 

 microphones at once, and they all seemed to respond with equal 

 force. Of course there must be a loss of energy in the conver- 

 sion of molecular vibrations into electrical waves, but it is so 

 small that I have never been able to measure it with the simple 

 appliances at my disposal. I have examined every portion of 

 my room — wood, stone, metal, in fact all parts, and even a 

 piece of india-rubber — all were in molecular movement when- 

 ever I spoke. As yet I have found no such insulator for sound 

 as gutta-percha is for electricity. Caoutchouc seems the best ; 

 but I have never been able, by the use of any amount at my 

 disposal, to prevent the microphone reporting all it heard. 



The question of insulation has now become one of necessity, 

 as the microphone has opened to us a world of sounds, of the 

 existence of which we were unaware. If we can insulate the 

 instrument so as to direct its powers on any single object, as at 

 present I am able to do on a moving fly, it will be possible to 

 investigate that object undisturbed by the pandemonium of 

 sounds which at present the microphone reveals where we 

 thought complete silence prevailed. 



I have recently made the following curious observation : — 

 A microphone on a resonant board is placed in a battery- 

 circuit together with two telephones. When one of these is 

 placed on the resonant board a continuous sound will emanate 

 from the other. The sound is started by the vibration which 

 is imparted to the board when the telephone is placed on it ; 

 this impulse, passing through the microphone, sets both tele- 

 phone-discs in motion ; and the instrument on the board, re- 

 acting through the microphone, causes a continuous sound to be 

 produced, which is permanent so long as the independent 

 current of electricity is maintained through the microphone. It 

 follovvs that the question of providing a relay for the human 

 voice in telephony is thus solved. 



The transmission of sound through the microphone is per- 

 fectly duplex, for if two correspondents use microphones as 

 transmitters and telephones as receivers, each can hear the other, 

 but his own speech is inaudible ; and if each sing a different 

 note no chord is heard. The experiments on the deaf have 

 proved that they can be made to .hear the tick of a watch, but 

 not, as yet, human speech distinctly; and my results in this 

 direction point to the conclusion that we only hear ourselves 

 speak through the bones and not through the ears. 



However simple the microphone may appear at first glance, 

 it has taken me many months of unremitting labour and study 

 to bring to its present state through the numerous forms each 

 suitable for a special object. The field of usefulness for it 

 widens every day. Sir Henry Thompson has succeeded in 

 applying it to surgical operations of great delicacy, and by its 

 means splinters, bullets, in fact all foreign matter, can be at 

 once detected. Dr. Richardson and myself have been experi- 

 menting in_lung-and heart-diseases, and although" the apph- 

 cation by Sir H. Thompson is more successful, I do not doubt 

 but that we shall ultimately succeed. There is also hope that 

 deafness may be reheved, for telephony articulation has become 

 perfect and the loudness increased. Duplex and multiplex 

 telegraphy will profit by its use, and there is hardly a science 

 where vibrations have any direct or indirect relation which will 

 iK)t be benefited. And I feel happy in being able to present this 

 paper on the results obtained by a purely physical action to such 

 an appropriate and appreciative body as the Physical Society. 



In conclusion, allow me to state that throughout the whole 

 of my investigations I have used Prof. BeU's wonderfully sen- 



sitive telephone instrument as a receiver, and that it is thanks to 

 the discovery of so admirable an appliance, that I have been 

 enabled to commence and follow up my researches in microphony. 



LABORATORY NOTES 



TOURING the daily routine of life in a laboratory many 

 observations are made of an isolated character, perhaps 

 having no direct bearing on the subject in hand, but which, 

 nevertheless, may be eminently suggestive to other minds. The 

 record of such observations are often lost ; they are not com- 

 municated unless they find a place in a larger research, and 

 they go to form the capital which every v/orker is accumulating 

 till his death, much of which, unfortunately, perishes with him. 

 I therefore cordially approve of the suggestion of the Editor 

 that workers in the various departments of experimental science 

 should occasionally write a few notes containing a brief account 

 of any observations recently made, and I shall be glad to con- 

 tribute my quota. 



I. Carl Zeiss' Neiv Oil Immersion Z<f;«.— This is a |th-objec- 

 tive, on the immersion system, in which the fluid used is oil of 

 cedar-wood. For amount of light, clearness of definition, re- 

 solving power, and flatness of field, it is superior to any lens I 

 have worked with. For use in histological observation, it does 

 not require any special arrangement of light. In examining 

 such objects as blood-corpuscles or salivary cells with very high 

 powers it is of great advantage to be able to use cover-glasses of 

 ordinary thickness, and to have a serviceably -working distance. 

 This is secured by Zeiss' lens. I have found that, with ordinary 

 Nos. 6 and 7 Hartnack-objectives, more light is obtained by 

 using them as immersion-lenses with a drop of equal parts of 

 oil of cedar-wood and olive oil. The method of using fluids of 

 high refractive index, on the immersion principle, seems to me 

 likely to lead to valuable results. With oblique light, cutting 

 off light from the mirror, the performance of Zeiss' lens is 

 remarkably good. 



2. The Phonograph as a Transtniiter, — By placing Hughes' 

 microphone on the disc of the phonograph the latter will 

 transmit the sounds recorded on the tinfoil to a telephone at a 

 distance. Thus we have a combination of microphone, phono- 

 graph, and telephone, which promises to be of use. It is very 

 suggestive to hear the phonograph speaking in one room and to 

 know that some one else in another room, or at a long distance 

 off, is also hearing a repetition of the sound. I have no doubt 

 that arrangements might be made by which the sound might be 

 reproduced in a dozen different places at once. 



3. The Working of the Phonograph. — After a good deal of 

 experience I have come to the conclusion that a thin and slightly 

 elastic membrane is the most suitable for loudness, whilst 

 a rigid non-elastic membrane is most adapted for distinct- 

 ness. From a consideration of the histological structure of the 

 drum of the ear this is what one would expect. After the im- 

 pressions have been made on the tinfoil, distinct speech, in a 

 feeble voice, of most peculiar quality, like what one would imagine 

 to be the tones of the fairies of old, can be heard from one of 

 Marey's tambours, by bringing the pDint of the lever on the 

 surface of the phonographic cylinder. With this method there 

 is almost no friction, and consequently the marks on the tin-foil 

 are not qmckly rubbed out. By connecting a tube with the 

 tambour and carrying it from the tambour to the ear, sounds 

 may be heard, even as speech, after the marks have been so 

 erased from the tinfoil as to be scarcely perceptible to the eye. 

 Thus the tambour, when so used, may be said to be a micro- 

 phone. 



4. The Microphone. — I have tried many experiments with the 

 ingenious arrangement of Mr. Hughes, and have been much 

 impressed with its extreme sensitiveness. It may be used to 

 make and break at pleasure the primary coil of the induction 

 machine. When fixed to the box of a monochord the slightest 

 touch of the wire with a camel-hair pencil sounds loudly in the 

 distant telephone. When placed on the sounding-board of a 

 piano, I have heard distinctly a complicated piece of music 

 eighty yards away ; when attached to the throat by an india- 

 rubber band, the faintest trill or whisper is audible; and it 

 transmits the muscular sound from a powerful biceps. 



5. A Lecture Experiment. — Place the heart of a frog on the 

 electrodes of Du Bois-Reymond in connection with a sensitive 

 reflecting galvanometer. The rhythm of the pulsations may 

 then be observed by the swinging to and fro of the spot of light 

 on a transparent screen. This has often been observed^ by 



