March 6, 1884] 



NATURE 



439 



well F. Varley. Both of those eminent men desired to investi- 

 gate the phenomena of mesmerism, which had been called 

 animal magnetism ; and they very earnestly set to work to make 

 a real physical experiment. They asked themselves, Is it con- 

 ceivable that, if a piece of copper can scarcely move through 

 the air between the poles of an electromagnet, a human bein;^ 

 or other living creature placed there would experience no effect? 

 Lord Lindsay got an enormrius electromagnet made, so large 

 that the head of any person wishing to try the experiment conld 

 get well between the pnles, in a region of excessively pnwerful 

 magnetic force. What was the result of the experiment? If I 

 were to f:iy iiolhing ! I should do it scant justice. The result 

 was marvellous, and the marvel is that nothing was perceived. 

 Your head, in a space through which a piece of copper falls as 

 if through mud, perceives nothing. I say this is a very great 

 wonder ; but I do not admit, I d > not feel, that the investii^ation 

 of the subject is completed. I canno' think that the quality of 

 matter in space which produces such a prodigious effect upon a 

 piece of metal can be absolutely w ithout any — it is certainly not 

 without any — effect whatever on the matter of a living body ; 

 and that it can be abiiolutely without Any perceptible effect what- 

 ever on the matter of a living body placed there seems to me 

 not proved even yet, although nothing has been found. It is so 

 marvellous that there should be no effect at all, that I do believe 

 and feel that the experiment is worth repeating ; and that it is 

 worth examining, whether or not an exceedingly powerful mag- 

 netic force has any perceptible effect upon a living vegetable or 

 animal bcdy. I spoke then of a seventh sense. I think it just 

 possible that there may be a magnetic sense. I think it pos-ible 

 that an exceeding powerful magnetic effect may produce a 

 sensation that we cannot compare with heat or force or any other 

 sensation. 



Another question that often occurs is, " Is there an electric 

 sense?" Has any human being a perception of electricity in 

 the air ? Well, somew hat similar proposals for experiment 

 might, perhaps, be made with reference to electricity ; but there 

 are certain reasons, that would take too long for me to explain, 

 that prevent me from placing the electric force at all in the same 

 category with magnetic force. There would be a surface action 

 that would annul practically the force in the interior, there would 

 be a definite sensation which we could distinctly trace to the 

 sense of touch. Any one putting his hand, or his face, or his 

 hair, in the neightiourhood of an electric machine perceives a 

 sensation, and on examining it he finds that there is a current of 

 air blowing, and his hair is attracted ; and if he puts his hand 

 too near he finds that there are sparks passing between his hand 

 or face and the machine ; so that, before we come to any subtle 

 question of a pos-ible sense of electric force, we have distinct 

 mechanical agencies which give ri-e to senses of temperature 

 and force ; but that this mysterious, wonderful, magnetic force, 

 due, as we know, to rotations of the molecules, could be abso- 

 lutely without effect — without perceptible effect — on animal eco- 

 nomy, seems a very wonderful result, and at all events it is a 

 -subject deservmg careful investigation. I hope no one will think 

 I am favouring the superstition of mesmerism in what I have 

 said. 



I intend to explain a little more fully our perceptions in 

 connection with the double sense of touch — the sense of tem- 

 perature and the sense of force — should tmie permit before I 

 conclude. But I must first say something of the other senses, 

 because if I speak too much about the senses of force and heat 

 no time will be left for any of the others. Well, now, let us 

 think what it is we perceive in the .sense of hearing. Acoustics 

 is one of the studies of the Birmingham and Midland In-titute, 

 of which we have heard many times this evening. Acoustics is 

 the science of hearing. And what is hearing ? Hearing is per- 

 ceiving someihing with the ear. What is it we perceive « ith 

 the ear ? It is something we can also perceive without the ear ; 

 something that the greatest master of sound, in the poetic and 

 artistic sense of the word at all events, that ever lived — Beet- 

 hoven — for a great part of his life could not perceive with his 

 ear at all. He was deaf for a great part of his life, and during 

 that period were composed some of his grandest musical com- 

 positions, and without the possibility of his ever hearins; them 

 by ear himself ; for his hearing by ear was gone from him for 

 ever. But he used to stand with a stick pressed against the 

 piano and touchmg his teeth, and thus he could hear the sounds 

 that he called forth from the instrument. Hence, besides the 

 Ear Gate of John Bunyan, there is another gate or access for the 

 sense of he.iring. 



What is it that you perceive ordinarily by the ear — that a 

 healthy person, without the loss of any of his natural organs 

 of sense, perceives with his ear, but which can otherwise be 

 perceived, although not so satisfactorily or completely? It is 

 distinctly a sense of varying pressure. When the barometer 

 rises, the pressure on the ear increases ; when the barometer 

 falls, that is an indication that the pressure on the ear is dimin- 

 ishing. Well, if the pressure of air were suddenly to increase 

 and diminish, say in the course of a quarter of a minute— sup 

 pose in a quarter of a minute the barometer rose one-tenth of 

 an inch and fell again, would you perceive anything ? I doubt 

 it ; I do not think you would. If the barometer were to rise 

 two inches, or three inches, or four inches, in the course of half 

 a minute, most people would perceive it. I say this as a result 

 of observation, because people going down in a diving bell have 

 exactly the same .sensation as they would experience if from some 

 unknown cause the barometer quickly, in the course of half a 

 minute, were to rise five or six inches — far above the greatest 

 height it ever stands at in the open air. Well, now, we have a 

 sense of barometric pressui'e, but we have not a continued indi- 

 cation that allows us to j^erceive the difference between the high 

 and low barometer. People living at great altitudes — up several 

 thousand feet above the level of the sea, where the barometer 

 stands several inches lower than at sea-level — feel very much as 

 they w'ould do at the surface of the sea, so fir as any sensation 

 of pressure is concerned. Keen mountain air feels different 

 from air in lower places, partly because it is colder and drier, 

 but also because it is less dense, and you must breathe more of 

 it to get the same quantity of oxygen into your lungs to perform 

 those functions, which the students of the Institute who study 

 animal physiology — and I understand there are a large number 

 — will perfectly understand. The effect of the air in the lungs 

 — the function it performs — depends chiefly on the oxygen taken 

 in. If the air has only ihree-quarters of the density it has in our 

 ordinary atmosphere here, then one and one-third times as much 

 must be inhaled, to produce the same oxidising effect on the 

 blood, and the same general effect in the animal economy ; and 

 in that way undoubtedly mountain air has a very different effect 

 on living creatures from the air of the plains. This effect is 

 disiinctly perceptible in its relation to health. 



But I am wandering from my subject, which is the considera- 

 tion of the changes of pressure com|jarable with those that 

 produce sound. A diving bell allows us to perceive a sudden 

 increase of pressure, but not by the ordinary sense of touch. 

 The hand does not perceive the difference between 15 lbs. per 

 square inch pressing it all around, and 17 lbs., or 18 lbs., or 

 20 lbs., or even 30 lbs. per square inch, as is experienced when 

 you go down in a diving bell. If you go down five and a half 

 fathoms in a diving bell, your hand is pressed all round with a 

 force of 30 lbs. to the square inch ; but yet y.iu do not perceive 

 any difference in the sense of force, any perception of pressure. 

 What you do perceive is this : behind the tympanum, is a 

 certain cavity filled w ith air, and a greater pressure on one side 

 of the tympanum than on the other gives rise to a painful sen- 

 sation, and sometimes produces rupture of it in a person going 

 down in a diving bell suddenly. The remedy for the pamfal 

 sensation thus experienced, or rather I should say its prevention, 

 is to keep chewing a piece of hard biscuit, or making believe to 

 do so. If you are cheuing a hard biscuit, the opeiation keeps 

 open a certain passage, by which the air pressure gets access to 

 the inside of the tympanum, and balances the outside pressure 

 and thus prevents the painful effect. This painful effect on the 

 ear experienced by going down in a diving bell is simply because 

 a certain piece of tissue is being pressed more on one side than 

 on the other ; and when we get such a tremendous force on a 

 delicate thing like the tympanum, we m.ay experience a great deal 

 of pain, and it may be dangerous ; indeed it is dangerous, and 

 produces rupture or damage to the tympanum unless means be 

 adopted for obviating the difference in the pressures ; but the 

 simple means I have indicated are, I believe, with all ordinary 

 healthy persons, perfectly successful. 



I am afraid we are no nearer, however, to understanding 

 what it is we perceive when we hear. To be short it is simply 

 this : it is exceedingly sudden changes of pressure acting on the 

 tympanum of the ear, through such a short time and with such 

 moderate force as not to hurt it ; but to give rise to a very 

 distinct sensation, which is communicated through a train of 

 bones to the auditory nerve. I must merely pass over this ; the 

 details are full of interest, but they would occupy us far more 

 than an hour if I entered upon them at all. As soon as we get 



