• ^4 



NA TURE 



[September 27, 1S94 



deprived of pro'.eids in the ima^o stage it l.\ys no ej^s. Of the 

 anatomical condition of the reprodactive or4ani in thj fliei 

 experimentally reared no evidence is vouchsafed. 

 Plymouth, September 15. J. T. Cu.n.\i\31IAM. 



"Darwinism is not Evolution." 



I WAS very much struck — having heard the aimir.ible reply 

 which Prof. Huxley gave to Lord Salisbury on the evening of 

 Augusts — 10 find a passage in " Darwin's Life and Letters " 

 (vol. iii. p. 13 which is tho exact counterpart of the chief point in 

 Huxley's retort. Darwin write-; to Lyell (March 12, 1S63) : "I 

 must feel convinced that at times . . . you have as completely 

 i;iven up b?lief in immutability of specific forms as I have 

 done. . . . I'he more I work the more satisfied 1 become 

 with variaiion and natural selection, but that part of the case I 

 look at as less important, though more interesting to me 

 personally." 



It was whispered in Oxford that Huxley had spoken of 

 r>arwinism lather lightly in crmparison with evolution. The 

 above-quoied passage shows that even in this respect Darwin 

 himself had >et the example. 



I have reason to believe that these illustrious examples will 

 not be very cenerally followed. A. A. \V. H. 



Utrecht, September 11. 



E xtraordinaiy Phenomenon. 



Having recently had before me your number of the 6lli insl.' 

 I feel very desirous to brinp under your notice, for insertion in 

 your journal, the description of a most extraordinary and 

 singular phenomenon as was observed by me at Llanberis, 

 N. Wales, on Sunday, August 26 last, about 10.30 p.m. ; 

 especially as I perceive that the time of my observation 

 coincides precisely with the lime recorded in that number by 

 John \V. Earle, at Gloucester, describing his observation of a 

 remarkable meteor which he discoveied. 



I was outside the hotel in Llanberis at 10.30 p.m. admiring 

 the lustre of the stars — for it was a cloudless night — when, 

 gazing upwards into the region of Cassiopeia, I was startleil by 

 a sudden llish from a brilliant effulgence of white light situated 

 proximately to the two stars of greatest magnitude in that con- 

 stellation, which immediately resolved itself into a clearly de- 

 fined disc, ab)ul three limes the diameter of Jupiter. After a 

 brief interval I observed a body of brilliant orange colour dis- 

 charged from the disc, which was projected directly towards 

 Perseus. This body assumed a form reseml)ling an elongated 

 flatfish, but terminating in a point, the disc forming a nucleus 

 to the appiiition, which was marvellous to behold ; but its 

 visibility provtil to be only of short duration, for the white 

 disc, or nucleus, suddenly disappeared, leaving the orange- 

 coloured mass 'juiescent for about half a minute, and then 1 saw 

 it fade away gradually, and it vanished out of my sight. 



The appear.incc of this strange body did not occupy more 

 than five minutes of time ; its dimensions in length 1 esiimated 

 was about fifteen degrees of arc. I likewise noticed an 

 important fact — that it evidenced no motion in space. 



During my]irofessional career, including Arctic and Equatorial 

 services, a great part was spent in nightly walchings, in which 

 all sorts o( meteoric phenojiiena came under my notice, yet I 

 never beheld one which manifoled such marked singularity and 

 dittinctivencss combined. I could only regret that no one was 

 at hand to affirm what I saw. 



With refciencc to the meteor observed by John W. Earle in 

 Ursi .Maj'>r, I wish to mention that a building excluded that 

 coDStellaiion from my sight, thcrcfoie it establishes a very 

 interesting and important (act that these two extraordinary 

 pbenoiuena, one In Ursa Maj ir, the other in Cassiopeia, were 

 KO distinctly notified by two observers so remote Irom each 

 other at the very same moment. 



Erasmus Ommannkv, Admiral. 



29 Connaught Square, \V., September 24. 



" Aurelia aurita" 



At the Plymouth Laboratory, in July last, I cxaniine.l 3S3 

 adult spccimcni of Aiirtlia aurita, and founri eight specimens 

 <2'o8 per cent. ) showing a numerical variation in the generative 

 sacs and buccal arms. 



One specimen with 3 generative sacs, 3 buccal arms, and 

 9 tentaculocysts. Three specimens with 3 generative sacs, 



NO. I 300, VOL. 50] 



3 buccal arms, and each one has traces of a fourth genera- 

 tive sac and a fourth arm. Two have S tentaculocysts. 

 and one has 10 tentaculocysts. One specimen with 

 5 generative sacs, 5 buccal arms, and S tentaculocysts. Three 

 specimens with 6 generative sacs, 6 buccal arms ; two have 

 II tentaculocysts, and one has 12 tentaculocysts. Si.y 

 specimens with the normal number of buccal arms and genera- 

 live sacs show a variation in the size and shape of the sacs. 

 There appears to exi-it a correlation between the generative 

 sacs and buccal arms, but the tentaculocysts vary inde- 

 pendently of the other organs. 



I found S7 specimens U2S percent.) showing a variation in 

 the number of tentaculocysts. Twenty specimens possess less 

 than the normal number, and the remainder show an excess. 

 The range of variation extends from 6 to 15 tentaculocysts. 



Edwaki) T. Browne. 



University College, London, September 15. 



Science in the Medical Schools. 



In the issue of Natike of September 20, I notice a 

 table of the scientific classes which are to be given in the 

 medical schools of Great Britain during the session 1S94-95. 

 In this table I find that the subject of ''biology or zoology " 

 is indicated by a cross ( x ) as being taught in all the 

 medical schools of Scotland with the exception of the 

 University of Aberdeen. Vou will, doubtless, allow me to | 

 point out that in this matter Aberdeen is in precisely the same 

 I'osition as Edinburgh and Glasgow. A course of zoology i- 

 delivered in the University of Aberdeen in the winter session. 

 and a second course in the summer session, and there is, in 

 addition, a course of practical zoology. 



University, Aberdeen. II. Alleyne Nicholson. ' 



ON THE DOCTRINE OF UISCONTINUITV OF 

 FLUID MOTION, IN CONNECTION WITH 

 THE RES/STANCE AGA/NST A SOLID 

 MOVING THROUGH A FLUID. 



§ I. ""p HE doctrine that " discontinuity," that is to say 

 -•- finite difference of velocity on two sides of a 

 surface in a tluid, would be produced if an inviscid in- 

 compressible fluid were caused to llow past a sharp edge 

 of a rigid solid ci'///; no 7'iicitiif sp^icC Muvcn fluid ami 

 st'/iif wm, I believe, first given by Stokes in 1S47.' 



It is inconsistent with the now well-known dynaiTiical 

 theorem that an incompressible inviscid lluid initially at 

 rest, and set in motion by pressure applied to its i 

 boundary, acquires ///(• unique distribution of motion 

 throughout its mass, of which the kinetic energy is less | 

 than that of any other motion of the lluid with the same 

 motion of its boundary. 1 



§ 2. The reason assigned for the formation of a surface I 

 of finite slip between lluid and lUiid was the infinitely | 

 great velocity of the lluid <// the edge, and the corre- ! 

 sponding negative-infinite pressure, implied by the ( 

 unique solution, un/i'ss the fluid is alliKi'cd to sfparate | 

 itself from contact 7(.'ith tlie solid. This an inviscid in- 

 compressible fluid certainly would do, unless the jjicssure 

 of the fluid were infinitely great everywhere except at the , 

 edge. In nature the tendency to very great negative ! 

 pressure arising from greatness of velocity of a fluid 

 flowing round a corner is always obviated by each one 

 of three defalcations from our ideal : — 



(I.) X'iscosiiy of the lluid, preventing the exceeding 

 greatness of the velocity. 



(11.) Compressibility of the fluid. 



(in.) Yielding-ness of the outer boundary of the fluid 



§ 3. Defalcation (I.) is in many practical cases largely 

 operative when air is the fluid ; but (II.) is also largely 

 operative in some veiy interesting cases, such as the 

 ',i.'histliiij^ of a strong wind blowing round a sharp corner 

 or through a chink ; the blowing against the sharp edge 

 in the emboucluire of an organ-pipe, and in the inouth- 



1 "Collected Papers," vol. i. pp. 310, 311. 



