April 2% 1876] 



NATURE 



511 



"wonders of the deep," in the shape of a square wooden box 

 with a glass bottom, which on being set on the water and looked 

 through, obviated the surface ripple, and permitted a clear view 

 into the coral caverns, some of which, by the way, were of great 

 beauty, natural aquarium tanks, hoary wth mosses and sea- 

 blooms, floored with coral sand and shells, and tenanted by 

 curious fishes of the most brilliant and varied hues. 



The huge rounded bosses of green growing coral among which 

 the surf-breaks resembled much the moss-covered granite- 

 boulders of a boggy Scotch glen. Here we found banks and 

 beds of the coral sand where it is formed at our very hands. 



The scales and half scales were here in a most perfect state, and 

 seemed to make up almost the entire mass of sand. It was easy 

 now to see the principal source of coral sand — at least at Santa 

 Cruz — and that what is seen on the beach is merely what is 

 found out here in a more finely divided state. 



Over all the reef about us, growing plentifully, was the living 

 weed which supplies these scales — the vegetable tissue covering 

 the calcareous interior beine of a dull-green like the living coral 

 itself. I procured a specimen of the growing weed, and also of 

 the sand from these beds where it is first formed and from the 

 beach ; but unfortunately I have lost these. I can only send you 

 seme of the dried skeleton, and append a rough sketch of it for 

 the benefit of readers. John Munro 



West Croydon 



Floating Radiometers 



In Mr. Crookes' paper reported in Naturk, vol. xiiL p. 489, 



occur the following words : " The envelope turned very slowly 

 a few degiees in one direction, then stopped and turned a few 

 degrees the opposite way." Assuming that this is rightly re- 

 ported, it is inexplicable to me how Mr. Crookes could have 

 written it. For, as the lawyers say, it is "void from ambiguity." 

 The whole question between Mr. Crookes and Dr. Schuster 

 appears to me to turn on the one point ignored by the former. 

 When the rotation of the envelope began, in which direction 

 was the first oscillation ? To say that the envelope first turned 

 in one direction and then in the other is simply to say that 

 it oscillated, which, while it is a shorter mode of expressing 

 the same thing, is an equally useless expression. The very nerve 

 of the problem lies in the point omitted. If the first oscillation 

 of the envelope was in the direction opposite to that of the mill, 

 it is surely incontestable that the kick, which caused it, could 

 not be ihe effect of any external force acting on the discs only. 

 Valentines, Ilford C. M. Ingleby 



Freece and Sivewright's "Telegraphy" 



It is neither usual nor becoming for authors to question the 

 judgment of a reviewer in dealing with thfir works, and although 

 I think that in your number (vol. xiii. p. 441) you have treated 

 the little work by Mr. Preece and myself with some severity, I 

 do not propose to depart from this wholesome rule. Neverthe- 

 less, I think it but right to point out that the reason why the 

 scientific part of the subject was so far left out was because this 

 had been already dealt with in another work of the same series. 

 Prof. Fleemingjenkin's text- book on "Electricity and Magnetism" 

 had appeared before that on "Telegraphy " was undertaken. In 

 the former " the part of science " had been so ably treated that 

 it became unnecessary and would have been out of place to go 

 over the same ground in a practical text-book which was to 

 appear in the same series. J. Sivewright 



On the Nature of Musical Pipes having a Propulsive 

 Mode of Action 



In the concluding paragraph of my last paper (Nature, vol. 

 xii. , p. 146), I brought under notice the remarkable difference in 

 the effect of increased diameter upon the two great classes of 

 pipes, regarded by me as referable to the fact of the mass of air 

 in the pipe being in the one class (thai of pipes with reeds of 

 wood or metal) under the influence of a propulsive current, and 

 in the other class (that of pipes with reeds of air, or flue-pipes), 

 under the influence of an abstracting ciurrent ; the distinction 

 thus manifested on the mode of action will, if clearly appre- 

 hended, enable us to reconcile many apparent anomalies in the 

 behaviour of pipes perplexing to inquirers. 



Considering a current simply as flowing, that is to say without 

 the energy which the word propulsive implies, the nature of a tube 

 or conduit is to cause fiiction between the walls of" the tube and 

 the particles of the substance flowing through the tube whether of 

 air or of water. The friction of air upon air is also a calculable 

 effect In organ-pipes of the class now in question we have to 

 recognise that we are dealing primarily with a current, with a 

 true transport of air through a tube, a current propelled, abruptly 

 arrested, and in a secondary stage converted into vibration ; 

 therefore all the conclusions arrived at concerning the propa- 

 gation of waves of vibration in tubes are suggestively appUcable 

 here, and in practice we find these conclusions verified. 



As regards ordinary tubes or conduits, Seebeck, following 

 Regnault and Kundt, has shown (Nature, voL i. p. 456) that 

 the effect of friction in retarding the velocity of a wave in 

 propagation is not so insignificant as might be supposed ; it is 

 greatest upon those of tones of highest pitch, and it increases 

 according as the diameters of the tubes are less. In musical pipes 

 of the propulsive class exactly the same relations are preserved, 

 and if two pipes of different diameters give the same pitch-note, 

 then the pipe of larger diameter' will prove to be of greater 

 length, in fact the opposite of the law obtaining in pipes of the 

 abstracting class. In a narrow pipe the friction is in excess, with 

 an increased diameter the current gains greater freedom, and coin- 

 cidently, that inner motion vibration is less impeded. Pipes of 

 this class, for brevity here called propulsive in action, the 

 tiumpets, posaunes, bassoons, oboes, have this characteristic that 

 the whole of the wind used passes through the body of the pipe 

 and makes its exit at the upper orifice. In flue-pipes on the 

 contrary the amount of wind actually passing up the interior of 

 the pipe is scarcely noticeable. The form of trumpets and the 

 like is conical, but the oboe has a special feature, its tube is very 

 slender, slightly enlarging upward, until at the top it suddenly 

 expands into a terminal shape called a bell. An actual com- 

 parison will afford the clearest illustration of the effect of form. 



Two pipes of the standard pitch 256 vibrations per second : — 



Trumpet. 

 Sounding Mid C. 



Diameter at root of reed | in. 



Diameter at upper orifice 3 „ 



Length from tip of reed 23! „ 



Obob. 

 Sounding iSIid C. 



Diameter at root of reed fin. 



Diameter at upper orifice \ „ 



Length from tip of reed 2\\ „ 



(including bell) 



The oboe bell is not ordinarily reckoned in the effective length, 

 yet it is not altogether to be disregarded ; from its juncture at 

 the tube and up to the rim 3 inches, with diameter expanding 

 from J to 1 4 inches. The influence of narrow bore will be best 

 exhibited by comparing with these the orchestral oboe where the 

 bore commences at -^^ and the note C is given by that portion 

 without the bell, and which will measure from the finger hole to 

 the tip of the reed only 194 inches. In the Chinese organ, or 

 "Little Shang," which, when in proper condition is most perfect 

 in relation of tube to pitch, the pipe sounding C octave above 

 oboe measures 9| in length, including the beak, and the bore 

 of the tube is barely \ inch, being cylindrical, not conical. The 

 reed tongue is so very small that a larger bore would be dispro- 

 portionate, the column of air seems well suited to the strength of 

 the reed, the pitch does not quite accord with our organ or our 

 concert pitch, but that will not affect the argument. What I 

 am anxious to point out is that these varying relations of pipes 

 result from a natural standard, which underlies all empirical 

 changes. The true standard for all instruments of the propulsive 



