JSbpthmiiku, liiOl.l 



KNOWLEDGE. 



193 



Founded by RICHARD A. PROCTOR. 



VoL.sxiv.] LONDON: SEPTEMBER, 1901. [No. 11)1. 



CO NTEN TS. 



On the Capricious Hearing of Certain Sounds at 

 Long Range. I'.y tlir Rev. .loiix M. I!ai ox, f.b.a.s. 

 (Illustrated) 



The Insects of the Sea.— V. Flies. hy Geo. IF. 

 C.lRrKNTF.K. i>.Br.(LOXD.) {Illustrated) ... 



Round Fain Head. liv Gbenvilie A. .1. C'oii:. m.k.i.a., 

 K.O.S ~ .. 



The Ringed Plains of the Mare Nubium. By E. Wai.tek 

 MaiM'KB. F.it.A.s. {Illustrated) " 



The Ringed Plains of the Mare Nubium. {Plate.) 

 The Great Southern Comet (1901 I ). By \V. F. 

 Dbnnixg, f.b.a.s. (Illustrated) 



Letters : 



Nova Persei. By A. Stanley Williams 

 DuiBiB Rainbow. Bt R. T. Lewis. Note li_v Eds. 



British Ornithological Notes. Couducted by Habht K. 



WiTHEKlli', K.Z.S., M.B.O.U. ... 



Notices of Books 



Books Received 



Obituary :— Eleaxoe A. Objiebod ; Sir Cutubert E. Peek, 



UABT. M A., F.S A., etc 



Notes 



Current Carcinology. By the Rev. Thoma.s H. K 



SiBBiiiyo, M.A., F.K.S., P.L.S., p.z.s. ( Illustrated J ... 

 Microscopy. Conducted by il. I. Cboss 



Notes on Comets and Meteors. By W. F. Denning, 

 F.B.A.S. 



The Face of the Sky for September. By A. Fowi.eb, 



F.B.AS. ... 



Chess Column. By C. D. Locock, b.a 



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 107 



207 

 20K 



2111) 



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21 \ 



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 215 



ON THE CAPRICIOUS HEARING OF CERTAIN 

 SOUNDS AT LONG RANGE. 



By the Rev. .Iohn M. Bach.n', f.r.a.s. 



The last has hardly yet been said a.s to the vagaries of 

 -.oiinds of long range. Dr. Davison has contributed to 

 Knowledge* a graphic record showing how at a great 

 manj' distant places the minute guns fired at Spithcad 

 on February 1st were distinctly audible; some of these 

 places, mainly lying to the N., being upwards of a 

 hundred miles away — while at the same time the sound 

 waves in the immediate neighbourhood of Spithead were 

 almost or quite imperceptible. Commenting on this. 

 Dr. Davison conceives that the sound waves were first 

 of all reflected by contrary winds over the heads of 

 observers, but were aftemvards brought down again by 

 favourable upper currents. The same authority states 

 that the report of guns, distant or otherwise, when 

 inaudible in Portsmouth or Winchester, may often be 

 distinctly heard from the more open or higher ground 

 outside these towns. 



* Khowlbbge, June, 1901. 



The bending upwards or downwards of sound waves, 

 which seems to have presented a problem to Sir .lohii 

 Ilorschell, has been explained by Sir G. Stokes a.s duo 

 to the general increase of the velocity of wind currents 

 with hcigiit above the ground. As a consequence of 

 this he maintains that the front of a sound wave moving 

 against the wind will be caused to lean backwards and 

 therefore its direction of nioliun to bo tilted ohli(|uely 

 upwards. Tyndall accepting this theoiy, and taking a. 

 hinged ladder out on to a common, satislicd himself liiat 

 a small bell which had been moved to leeward until its 

 sound was inaudible could be distinctly heard w-hcn he 

 climbed high enough to catch the sonorous waves that 

 were being deflected upwards. 



It is here that I would offer a few observations of my 

 own as mainly sup])ortiiig the above. On one occasion, 

 when making a balloon ascent from Newbury, I caused 

 I he leiior bell of Tliatcham Clnircli, weighing uinvards 

 (if a ti)ii, and distant scarcely three miles to windward, 

 (o Ijc set ringing as in peal. The wind was a lij^hl 

 breeze, and the balloon iiiaintaiiicd altitudes vaiyini; 

 hetwceii lOOO and tin- ISdDO feet, yet the bell wa.s in- 

 audible to each and all of the four observers in the car. 

 It is true '.hat for the liist few iiiinutes there was much 

 noise in the air occasioned by the shouting of the crowd, 

 but. afterwards we travelled only over quiet agrictdtural 

 country. Another noteworthy phenomenon, to prove 

 which there is abundant evidence, is that when fog- 

 signals arc being fired from the Bishop lighthouse these 

 will sometimes sound so loudlv in the lower part of 

 Hugh Town and Forth Cress.i at St. Mary's Island, 

 eight miles away, as actually to shake the houses, while 

 the reports may be scarcely audible from the high and 

 open ground above. Once again I may mention that the 

 guns which, as Dr. Davison states, were tinheard at 

 Newbury, forty-four miles away in low ground, were 

 also inaudible from my own grounds in the neighbour- 

 hood, which are nearly .500 feet above sea-level. In the 

 above cases due account, must of course be taken of 

 any local turmoil in the air which may have tended to 

 ma.sk the distant sounds. In proof of this I may give 

 a recent ex])criment. A powerful reed was blown at the 

 focus of a large paraboloidal shell, the open moutli of 

 which was directed towards distant clumps of trees in 

 full foliage, when echoes were returned lasting for as 

 much as seven seconds, there being an absence of wind 

 at the time and the summer night well advanced. 

 Other things being equal, however, the same echoes 

 were lost after fovu' or five seconds if there were but 

 faint sounds in the air such as those of bird or insect 

 life. This is tantamount to proving that a local dis- 

 turbance which is scarcely noticeable may reduce the 

 lange of a given sound by almost one-half. 



Further, it may be a question whether the natui-e of 

 the earth may not in some way affect long hearing. 

 Bearing on this. Lord Rayleigh makes' the suggestive 

 remark : " The propagation of earthquake disturbance,'' 

 he says, " ijs probably affected by the curvature of the 

 surface of the globe acting like a whispering gallery, 

 and perhaps even sonorous vibrations generated at the 

 surface of land or water do not entirely escape the same 

 kind of infiuence. ' 



Again, surrounding covintry may make a vast 

 difference in redoubling a sound at any given point or 

 else in allowing it to escape. A remarkable instance of 

 this came under my notice lately. For signalling 

 purposes I was firing gun-cotton fog-signals on the open 

 ground at Chcetham Hill, Manchester, between ten and 



