April I, 1875J 



NA TURE 



427 



3. Prof. Nipher, old series, right arm 2"oSo o'i26 



4- ), _ left arm 2-060 0-137 



5. ,, new series 2-560 0-194 



Alsojevons: a- 1-74 + A;T)b ; Nipher: a = 1-28 + 6-251'', 

 very nearly. 



To extend the law beyond the above physiological limits, 

 introduce the coefficient i>f restoration , r, and of paiu, p, in 



jV= (l + r -f]n (2) 



where both from theory and by above series of experiments, 



/ = ;# 



1 have no doubt that / is of the same form ; but none of the 

 above series have been continued far enough to sufficiently con- 

 firm this. It is evident that / vanishes for small values of w, 

 and r for large values of 10, 



These few remarks may be sufficient to show that the earlier 

 as well as the late experiments of Frof. Nipher constitute a very 

 valuable contribution to Animal Mechanics. 



Iowa State University, Feb. 22 GusTAVt;s HiNRiCHs 



The Height of Waves 



Your correspondent Capt. William W. Kiddle, in Nature, 

 vol. xi. p. 3S6, speaking of the height of waves, says : — "This 

 remarkable gale swept over a portion of the Atlantic which the 

 French call ' Le trou de diable.' . . . When the wind sets 

 strongly in this direction from the north-west, the sea rises in an 

 incredibly short space of time, and at the close of a long winter 

 gale it is a grand sight to watch the great waves," &c. The 

 question is then a^ked, why this remarkable phenomenon occurs 

 ■with a north-west gale, whilst with an equally strong south-west 

 or southerly gale the effect is insignificant ? 



I think an explanation may be given thus : — " Le trou de 

 diable " — whose position, roughly calculated, is 45° N. and 

 40° W. — is, roundly speaking, about the centre of the Clulf 

 Stream in that locality, and during a strong north-west gale the 

 wind meets the Gulf current at a good angle. The force of this 

 encounter h.as a tendency to drive the stream out of its course. 

 The velocity of the water-current and its mass are, however, so 

 great that it yields but slightly, if at all ; consequently, the force 

 of the wind exerts itself to a large extent in banking up the 

 ■water to the production of unusually high waves. 



From an analogous course of reasoning, it is apparent that a 

 south-w-est or southerly wind -tt-iU not have a similar effect ; for 

 both stream and wind are then travelling in the same, or nearly 

 the same, direction. The force of a gale from the south-west 

 or south has no counter water-force to oppose it ; hence its high 

 velocity tends simply to increase that of the Gulf Stream, as well 

 as to beat down its surface to the prevention of any extraordi- 

 nary waves. Arthur R. Granville 



Islington, March 22 



Thermometer Scales 



The thermometric scale referred to .by Mr. T. Southwell 

 (Nature, vol. xi. p. 2S6) was, I believe, one used and invented 

 by Fowler, in which o = 55° Fahr., 75 above = 102° Fahr., and 

 So below - -y l" Fahr. 



The above equivalents are only approximately given. Fcr 

 full desciiption, &c., see "Essays on Construction and Gradua- 

 tion of Thermometers," by Geo. Marline, M.D, 1772 : Edin- 

 burgh. 



I have failed so far in discovering the scale of Linnjeus alluded 

 to, and shall likewise feel irdebted to any of your readers who 

 will describe it. S. G. Denton 



34, Foreign Street, Brixton, March 23 



Accidental Importation of Molluscs and Insects 

 I OBSERVE in Nature (vol. xi. p. 394) a rote from the Saar 

 und Mosel Zeitiing on the introduction of a mollusc into the 

 Moselle near Ti eves. Though the name of the species is not 

 mtntloned, I presume that Drcisscna polyiiwrpha is the moUufc 

 in question, a species known to inhabit Britain since 1824, and 

 supposed to have been introduced wuh timber from Eastern or 

 Northern Europe. It is exceedingly prolific. An instance of 

 how this species may be introduced came under my notice a few 

 years ago. A friend showed me some shells that he had found 

 attached to logs of -n-ood lying on a railway truck. These proved 

 to be alive when put into a cup of water ; and if the logs in 



question had been deposited on the banks of the Tay within 

 reach of the tide, as is often the ca.e (I should have said that the 

 truck was on a sidmg near Perth Harbour), we would no doubt 

 have found Dreissena in abundance in the course of a few years 

 As this mollusc lives in brackish water as well as in fresh, it is no 

 doubt in a manner similar to what I have mentioned that it has 

 been introduced into and spread through Britain. Another shell 

 riaiiorUs lii/atatiis, a North American species, was found a few 

 years ago living in a canal near Manchester, and is supposed 

 to have been introduced with raw cotton. Recently another 

 case of importation of living shells came under my notice. 

 When looking at some hales of Typ/ia from the Nile, imported 

 into Aberdeenshire as a material for paper manufacture, I 

 observed some shells sticking in the dry mud adhering to the 

 roots of the Trp/ia. On putting some of these into water they 

 were found to be alive, though a good many months had elapsed 

 since the Tyffia had been gathered. The shells appear to belong 

 to Bythinia, but I have not yet determined the species. It is, per- 

 haps, not very likely that if these shells had found their way into 

 the Aberdeenshire rivers they would have survived. 



Land molluscs are sometimes introduced, and several European 

 species have in this manner become naturalised, in North 

 America. 



Apropos of the fears that have been expressed that the Colo- 

 rado Potato Beetle (Doryphora d.cemlincala) may be introduced 

 into Europe and prove destructive, the Entomological Society of 

 Belgium has been recently discussing the matter, .and has ar- 

 rived at the conclusion that the fears regarding this insect are 

 much exaggerated. M. Oswald de Kerchove, of Denterghem, 

 has just published a very complete memoir upon this beetle. He 

 thinks that it is very improbable that the Dorvpliora will be in- 

 troduced, and at any rate that the prohibition of the importation 

 of American potatoes is unnecessary, as it lives upon many other 

 plants than Solaiiacca: M. de Kerchove further deprecates the 

 use of the arsenite of copper (Scheele's green), so much em- 

 ployed by the Americans tor the destruction oi the beetle, as 

 such a dangerous substance ought not to be made common. 



Is not the " Blood Louse," so destructive to apple-trees, men- 

 tioned by,lhe Koltiische Zaliiii^ (Nature, I.e.), the homopterous 

 Eriosoma lanigera, the so-called American Bug, already too well 

 known in this country ? 



Perth F. Buchanan White 



Fall of a Meteor [at Orleans 



In the " Notes " of March 18 (vol. xi. p. 396) it is stated that 

 a meteor fell in a street at Orleans on the gtn inst. The time of 

 the fall is not mentioned, but it would be interesting to know if 

 the meteor were the same that was observed from here on the 

 evening of that day about eight o'clock. It was very brUliant, 

 as bright as Sirius, and moved slowly from a position a few 

 degrees to the east of Sirius, in a south-easterly direction, the 

 path making with the horizon an angle of about 60°. 



Cooper's Hill, March 27 Herbert M'Leod 



Proposed Aquarium in Edinburgh 

 I am happy to be able to inform you that the suggestion 

 originally made in Nature, that a large aquarium should be 

 formed in Edinburgh, is likely soon to be adopted. A company 

 named the "Edinburgh Winter-Garden, Theatre, and Aquarium 

 Company (Limited) " proposes to provide at the west end of 

 Edinburgh a large and well-stocked aquarium on a scale not 

 inferior to those of Brighton and the Crystal Palace. 

 Edinburgh, March 26 Ralph Richardson 



Acherontia Atropos 



Can any of your readers throw any light on the raison d'etre 

 of the dimorphism of the larva of the Death's-head Moth 

 (AcJieivntia atropos) ? Some years ago I found five larvir of this 

 insect on a bush of jasmine. They were all probably offspring 

 of one female. Two of them ^^ere of the dark chocolate- 

 coloured variety so strikingly dissimilar to the normal orcommoner 

 type. The imago 01 rne ol the dark-coloured larvre differed in no 

 respect that I could perceive from the ordinary form. It has 

 occurred to me that the dark variety may be due to its simulating 

 the dead, withered, blighted, or diseased shoots of the potato, as 

 its commoner brother does the healthy leaves and st.alks. 



Taunton ^ , Fred. P. Johnson 



