May 30, 1878] 



NATURE 



129 



THE MICROPHONE 



"IX /■£ have received the following communications on 

 '' • this subject : — 



At a discussion upon Mr. William Preece' s paper on 

 the microphone, which took place before the Society of 

 Telegraph Engineers on Thursday last, the Duke of 

 Argyll called attention to the important part which that 

 invention was Ukely to play in physiological research. As 

 chairman of the meeting I took occasion to refer to the 

 intimate connection between the microphone and its two 

 elder sisters, the telephone and the phonograph, in con- 

 junction with which it formed a discovery which would 

 probably be hereafter regarded as one of the greatest 

 achievements in natural science of the present century. 

 I ventured further to draw an anology between the action 

 of the phonograph and the action of the brain in the 

 exercise of memory, and with your permission I will 

 enlarge upon this speculation to the extent of making my 

 reasoning clear enough to submit the same to the critical 

 test. 



All impressions received by us from without, either 

 through the tympanum of the ear, the retina of the eye, 

 or through the sensitive nerves of the skin, are, it is 

 generally believed by physiologists, communicated to 

 corpuscular bodies in the brain, which lie embedded in a 

 grey substance, the nature and precise function of which 

 have not yet been fully explained. It would appear that 

 the corpuscular bodies in which the sensitive nerves ter- 

 minate are connected, through the medium of extremely 

 delicate filaments, with the nervous system of volition, 

 the reaction of the one system upon the other being 

 attributable to mental energy. It may be conceived 

 that any fresh impressions received on the ex- 

 tremely complex sensitive network of the brain may 

 give rise then and there to acts of volition ; but 

 how, it may be asked, can acts of volition arise from 

 impressions that were communicated through the sensi- 

 tive nerves yeai-s before, having been committed in the 

 meantime to what we term the memory ? But in order 

 that the mind can deal with an impression previously 

 received it seems necessary" that it must have the 

 power of reproducing the same from some material 

 record by which the impression has been rendered 

 permanent. Take the case of a tune that we have 

 heard in early youth and which may not have since 

 recurred to us. By some incident or other that tune and 

 the words connected with it become suddenly revivified 

 in the mind, If the tune had been sung into a phono- 

 graph it could have been reproduced at any time by 

 releasing a spring moving the barrel of the instrument ; 

 and it seems a fair question to ask whether the grey 

 substance of the brain may not, after all, be something 

 analogous to a storehouse of phonographic impressions 

 representing the accumulated treasure of our knowledge 

 and experience, to be called into requisition by the 

 directing power of the mind in turning on, as it were, one 

 barrel or another. 



Such a hypothesis might possibly serve also to explain 

 how in sleep, when the directing power of the mind is not 

 active, a local disturbance in the nervous system may 

 turn on one or more phonographic barrels at a time, and 

 thus produce the confused images of dreamland ! A 

 powerful mind would exercise a complete control over the 

 innumerable barrels constituting our store of knowledge, 

 whereas in a weak mind the impressions of the past would 

 be brought back into evidence in a confused and irregular 

 manner. Such a supposition might also account for the 

 more vivid recollection of impressions received in early 

 life, when the mechanical record stored up in the brain 

 may be supposed to have been more distinctly and 

 indelibly rendered. In speaking of these impressions as 

 phonographic it does not follow that they were origi- 

 nally conveyed through the tympanum of the ear. Mr. 



Willoughby Smith, at the meeting above referred to, 

 called attention to the fact that, by substituting crystal- 

 line selenium for carbon in the microphone, a ray of 

 sunlight directed upon the selenium produces a noise 

 comparable with that produced by a Nasmyth hammer; 

 and it is quite feasible that the impressions received 

 through the retina of the eye, and the nervous system 

 generally, would be equally susceptible of being recorded 

 in the cerebral storehouse. The record itself might be 

 supposed to be of a mechanical, or, more probably, of a 

 molecular character, the one thing important being that 

 it must be material. 



These observations are, no doubt, extremely crude, 

 but may serve possibly to direct the attention of physio- 

 logists to a point of interest to their science ; nor would 

 it be the first occasion on which a phenomenon of in- 

 animate nature had revealed the secrets of animate 

 organisation. 



C. William Siemens 



I HAVE been much interested in your account of the 

 microphone of Prof. Hughes, and I have made, as doubt- 

 less many of your readers have also done, the different 

 forms of instrument described by him. The action of the 

 instrument is there apparently attributed to the change of 

 conductivity of the charcoal or carbon or of the mercury 

 globules therein, under the influence of sonorous waves ; 

 and whether this is correct is a question worthy of consi- 

 deration in your columns, and I therefore write more for 

 the purpose of leading others into the inquiry than of 

 making assertions on the subject. My experiments point 

 to another cause, viz., the variation of conducting sec- 

 tional area of a bad conductor due to the increased or 

 diminished pressure on the point of contact. I am not, 

 of course, referring to the action of the instrument when 

 the vibration is sufficient to absolutely sever the contact, 

 which simply causes the telephone plate to vibrate either in 

 its own period, or some other than that due to the acting 

 sound, as is the case when a musical box is placed on the 

 same table with the instrument ; but to the forced or 

 articulate vibrations— the reproduction of the sound 

 acting on the microphone. 



Of the several forms of instrument described by Prof. 

 Hughes I have chiefly used that consisting of a rod of 

 charcoal pointed at both ends, supported in a vertical 

 position with its lower point resting in a hollow in a 

 similar piece of charcoal, while its upper end rests against 

 the sides of a similar hollow above. This form is extremely 

 sensitive, and it is difficult to prevent the circuit being 

 broken while having it sufficiently near the source of 

 sound to be reproduced; the sound of a musical box is 

 perfectly rendered, when so far away that there is an 

 absence of jarring from breaks in the circuit ; but in 

 talking to the instrument, any rise in the voice breaks 

 contact and produces the jarring sound in the telephone, 

 to the exclusion of all articulation. 



I find that any sort of charcoal or carbon will answer, 

 whether soaked with mercury or not ; I therefore con- 

 clude that the mercury has little or nothing to do with 

 the action. I have tried the effect of sound on rods of 

 carbon and charcoal both saturated with mercury and 

 not so saturated, so arranged that the vibrations could 

 not alter the area of contact, and have obtained no sound 

 whatever from the telephone in the circuit ; I therefore 

 conclude that the action takes place at the point or points 

 of contact, and is due to the change of conducting area. 

 To Prof. Hughes is due the credit of inventmg a 

 means of varying the electric current with extreme 

 rapidity and slight motion without absolutely breaking 

 the circuit, but I doubt whether a microphone is a proper 

 term for describing the instrument. In gently brushing 

 the stand of the instrument, sound is heard in the tele- 

 phone, but it does not at all follow that what we hear is 

 a magnified reproduction of the brushing sound ; for if 

 the rapidity of the vibrations or motion produced by 



