270 



NA TURE 



\Jucy 19, 1883 



variety, and when such interference takes place the tone is 

 always meagre, as described by Dr. Hnggins. 



But it will naturally occur that there must be one note in the 

 scale of the instrument which will coincide in its vibrations with 

 those of the belly when in this un upported condition, and that 

 this note ought to be exceptionally loud. It is so in fact, but 

 not to the extent that might at first be supposed. This is 

 because in reality, as I shall try to explain, the injurious effect 

 of interference does not include the whole question. When a 

 tuning-fork is struck and held out of contact with a resonant 

 body, it gives out a very feeble sound. The cause of this, as is 

 well known, is that each half-wave is compensated and pirtly 

 annulled by the succeeding half taking place in the opposite 

 direction. A string stretched between two non-resonant sup- 

 ports does the same when plucked or bowed in the middle. In 

 like manner, the belly of a fiddle, when unsupported by a sound- 

 post, is under conditions which are very similar to those of the 

 string. The most yielding part is immediately beneath the 

 bridge, under the impulses of which every point of every longi- 

 tudinal fibre moves up and down in the same pha<e, and every 

 half-vibration cancels the effect of the half immediately pre- 

 ceding. The sound is correspondingly feeble. The wave, in 

 fact, is not a true one. It is a to-and-fro, self-compensating 

 motion all along the line. If the bridge were placed near one 

 end of the instrument, the ca e would be different. Its near- 

 ness to a support or fulcrum on one side would cause the free 

 part on the other side to break into a wave of progression, which 

 is the true dynamic sound-giving wave. The office of the sound- 

 post is precisely this. It forms a node at a particular part under 

 the influence of which the wave is converted into one of contrary 

 phases all over the surface. Such a wave travels in wood at 

 amazing rapidity, and the consequence is that every half vibration 

 reaches its limit and strikes the air almost before the other half 

 has commenced its career, and therefore before it has hail time to 

 interfere with its dynamic effect. The best position of the node 

 is found to be just behind the E string, because the higher the 

 note the greater is the firmness required. The G siring is 

 further removed from the support, because the lower notes 

 require greater freedom of motion, but it still partakes of its 

 advantages. 



I have never met with a satisfactory explanation of the cause 

 of resonance in sound-boards. It cannot be due to extended 

 surface in the sense that there are more extended vibrations or 

 more numerous ones, because tbe greater the quantity of matter 

 put in motion the more is the motion diluted. The investigation 

 is practically a difficult one, owing to the extreme minuteness of 

 the oscillations which have to be traced, but so far as the experi- 

 ments indicate which I have been able to devise, the true cause 

 does seem to be what I have been endeavouring to explain. A 

 resonant wave is a travelling wave — the crest is alwavs in 

 advance of the depression, and expends itself dynamically before 

 the latter has time to neutralise it. On the other hand, the 

 depression succeeds in due order and produces a similar effect. 

 It is in this sense only that an extended surface is useful and 

 necessary. 



If we need confirmation of the principle thus advanced, we 

 have it in every wind instrument without exception. The type 

 of all such instruments is the reed, the only difference being that 

 in some it is aerial, and in others substantial. Take therefore 

 an ordinary harmonium reed, and vibrate it with the finger. 

 However elastic it may be, the sound is of the feeblest character. 

 The d iul)le vibration is a compensated one — but let a current of 

 air traverse the point of disturbance, the reed then speaks, or 

 rather the current of air speaks. The half vibration has pro- 

 ceeded so far from its origin that it expends its dynamic force 

 before the succeeding half is able to reach and neutralise it — the 

 crest of the wave, as it were, has smitten the shore, before the 

 depression has had time to overtake it. The depression then 

 succeeds and does its own work. R. HoWSON 



Middlesbrough 



Waking Impressions 



The accompanying experience may be of interest to some of 

 your readers ; and that it may be the more genuine in the re- 

 counting of it, I copy the little entry I made in my notebook 

 some few hours only after the occurrence, as it was so distinctly 

 impressed on my mind that I could not but be struck by it as 

 being worth taking note of. 



I have not unfrequently been on the point of noting down 



similar visual impressions between sleeping and waking time, but 

 have hitherto always found that tbey were really of so fugitive a 

 nature, or the mind so little sensitive as not to be retentive, that 

 the mere effort to recall them and put them into uttered words 

 (whether audibly or only mentally uttered) was quite sufficient 

 to dispel the impression totally ; though by a long directing of 

 the memory I could sometimes nearly recover it, not perfectly 

 enough, however, to feel confident that imagination had not 

 added somewhat to the picture. But the present case has been 

 so vividly impressed on my mind that it has been fairly caught, 

 to my own satisfaction at any rate, and I hope that it may be 

 not unworthy of a corner in your valuable paper. 



"Ungate, July 13 

 " This morning I woke up suddenly with the end of a dream and 

 found myself reading, as if from a printed book, only there was no 

 book, merely printed words, thus : ' So while hewas enjoying himself 

 at ... . she was in deep depression at Kay-ro.' The ' Kay-ro ' 

 looked quite right, and I quite naturally pronounced it Cairo, 

 and knew I meant that town. I was so struck by the clearness 

 of the visual impression that, for fear of losing it, as one gene- 

 rally does, I instantly recounted the thing to my husband ; but 

 in the uttering of it when wide awake I could not at the moment, 

 even so soon after the dream, recollect the name of the other 

 locality (marked here by ' . . . . ')> though I knew that it had 

 been printed and read by myself in the dream. But about four 

 minutes later, as we were talking it over, I said, ' It is so 

 strange, for I'm sure I've not been talking or thinking either of 

 Beloochistan or Cairo ! ' and at once it flashed upon me that 

 Beloochistan had been the other name, and I had then and there 

 reseen the impression after an interval of total oblivion of it. 



" There had been no idea of book or sheet to carry the printing, 

 nor, I fancy, even solidity of any kind in the letters ; but that 

 the whole phrase was conveyed to my mind through a printed 

 form and by a process of reading I am quite certain. We were 

 on a visit, and the night before had been greatly entertained by 

 the conversation of our host, who had been a great traveller, 

 and we had certainly talked much of India, Cashmere, and 

 Assam ; but as far as I can now, or could then, recollect, we had 

 most certainly not mentioned either Beloochistan or Cairo, nor 

 had I been reading a novel before going to sleep or during the 

 previous day." 



Collingwood, Hawkhurst, July 14 J. Maclear 



Tertiary Corals 



I shall be obliged if you or any of your readers would kindly 

 inform me the best authority to consult on the tertiary corals of 

 Piedmont and Lignria ; also the age of the beds in the lower 

 part of Val d'Andona. W, E. Balston 



Bearsted House, Maidstone, July 15 



Wild Fowl and Railways — Instinct and Intelligence 



I am happy to find that my experience of " ducks and rail- 

 ways " is confirmed by so high an authority as Mr. Goodsir from 

 observations made on the other side of the world. Agreeing so 

 far, we differ as to the cause by which the birds are influenced, 

 Mr. Goodsir attributing it to "quick and unerring instinct," 

 whilst I credit the ducks with "quick intelligence" or reasoning 

 powers. If caused by the "teaching" of instinct, the ducks 

 should show no alarm on the sudden and first appearance of a 

 smoking, roaring train in their midst. They certainly do at first 

 show alarm, but as they receive no injury, their intelligence 

 teaches them, after a brief experience, that there is no danger. 



I may perhaps be permitted to give one of many instances 

 known to me of the quickness of birds in acquiring a knowledge 

 of danger. Golden plover, when coming from their breeding- 

 places in high latitudes, visit the islands iv>rth of Scotland in 

 large numbers, and keep together in great packs. At first they 

 are easily approached, but after a very few shots being fired at 

 them, they become not only much more shy, but seem to 

 measure with great accuracy the distance at which they are safe 

 from harm ; the sportsman, however, not unfrequently takes an 

 unfair advantage of them by loading with a wire cartridge, 

 which adds twenty yards or so to the distance at which the gun 

 will kill when charged in the ordinary way. 



It would be easy to adduce many cases of what may be con- 

 sidered pure and true instinct, of which the following is perhaps 

 not a bad example, and not unworthy of mention, if it has not 

 already appeared in the columns of Nature or elsewhere : — 



