September 2, 1897J 



NATURE 



419 



British Rainfall, 1896. By G. J. Symons, F.R.S., and 

 H. Sovverby Wallis. Pp. 221. (London: Edward 

 Stanford, 1897.) 

 Mr. Symons has now 3219 observers who send him 

 rainfall statistics from different parts of the British Isles. 

 On the average, there is one rainfall station in every 21 

 square miles in England, one in every 36 square miles in 

 Wales, one in 74 square miles in Scotland, and one in 

 179 square miles in Ireland. The task of editing the 

 records obtained at all these stations is thus a heavy one, 

 and it becomes heavier every year on account of the 

 increase in the number of observers. Unfortunately, 

 the tendency is for observers to increase in districts 

 already adequately supplied with rainfall stations, and to 

 decrease in districts where stations are badly needed. 

 In Scotland and in Ireland there are areas of several 

 hundred square miles without a single observer, and in 

 the county of Sutherland, which contains over two 

 thousand square miles, there are only six stations, three 

 of which are so close together that they may be regarded 

 as one. It is to be hoped that ne.xt year the editors of 

 " British Rainfall " will be able to report that Sutherland 

 is giving more assistance than it does now to a know- 

 ledge of the rainfall of the county. 



In addition to the usual discussion of the rainfall and 

 meteorological observations of 1896, and general tables 

 of total rainfall, the present volume contains short 

 anicles upon the rainfall in the vicinity of Seathwaite — 

 the most rainy part of England— evaporation experi- 

 ments, the Heberden family and meteorology, and a com- 

 parison of German and English rain gauges and of Mr. 

 Sidebottom's snow gauge. 



LETTERS TO THE EDITOR. 



{The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonytnous communications. ] 



The late Earthquake in India. 



Mr. R. D. Oldham, Director of the Geological Survey of 

 India, has written to me for particulars of the photographic 

 record of the Calcutta earthquake of June 12, 1897, as shown 

 by the horizontal pendulum of this observatory. As Mr. 

 Oldham is preparing a full report on this earthquake, he has 

 also asked me to let it be known that he would esteem it a 

 favour if copies of all records of its effects, wherever it has 

 left any traces, be sent to him at the " Geological Survey Office, 

 Calcutta." Ralph Copeland. 



Royal Observatory, Edinburgh, August 24. 



On Mimicry. 



In a letter on p. 197 of Nature, which I saw only a few 

 days ago, Mr. Walter F. H. Blandford, referring to my sugges- 

 tion as to the scarcity of individuals of mimetic species of Lepi- 

 doptera, rightly insists, that it has first to be shown that there is 

 correlation between the acquirement of mimetic resemblance 

 and the production of small numbers^of specimens, before my 

 suggestion becomes acceptable, and adds, that the advantage 

 which the imago state of Lepidoptera probably derives from the 

 resemblance to an immune model may possibly be counteracted 

 Ijy increased destruction in other stages. NIr. Blandford has 

 apparently not taken into account what I thought to be too well 

 known to need fuller explanation, and hence touched only by 

 stating that " so many mimetic species are scarce, in comparison 

 with the non-mimetic allies," namely, that the number of rare 

 forms amongst mimics is remarkably greater in proportion than 

 the number of rarities among their non-mimetic allies. This 

 excess of scarcity among mimics Mr. Blandford's assumption of 

 increasing destruction in the larval states does not meet, unless 

 we assume, further, that only rare species can become mimetic, 

 or that the excess of rarity among the forms which have become 

 mimetic is due to the acquirement of mimetic resemblance, i.e. 



NO. 1453, VOL. 56] 



that there is the kind of correlation which my suggestion (p. 153) 

 requires. In support of the latter alternative — the former does 

 not concern us here — I adduce the following statements, at 

 which I arrived by a comparison of the mimetic and non- 

 mimetic forms of those two groups of Eastern Papilios among 

 which mimicry occurs (Haase's subgenera Cosmodesmus and 

 Papilio, s. str. ). 



(i) According to a rough estimate the proportion of the 

 number of rare mimetic forms to the number of more common 

 mimetic forms of Eastern Papilios is approximately as I : 2, while 

 the proportion of the number of rare non-mimetic forms to the 

 number of more common non-mimetic forms is as i : 4 ; that is 

 to say, the number of rarities is among mimics about twice as 

 large proportionally as among their non-mimetic allies. These 

 numbers are, of course, not quite correct, as our knowledge of 

 the insects in question is far from being complete. I add, 

 incidentally, that the proportion of the rare to -the common 

 forms is as I : 2 in that group of Eastern Papilios which feed as 

 larvoe on Aristolochiacece, and partly serve as " models." 



(2) The mimetic species which are mimetic only in one sex, 

 or resemble the model only superficially, are generally common. 



(3) The mimetic species which are very variable are common, 

 at least commoner than their less variable allies. 



(4) The mimetic forms which agree very closely with the 

 model in both sexes are the rarest («/. Haase, "Mimicry," ii. 

 p. 116 : Stuttgart, 1893). 



These four points are decidedly in favour not only of there 

 being a connection between the acquirement of mimetic re- 

 semblance and the scarcity of individuals, but also of the excess 

 of scarcity among the mimics being a consequence of the 

 development of the mimetic characters. It does not seem to 

 me to be far-fetched to say — as others have said before me — 

 that rigorous adjustment of a species in one special direction 

 (by Neo-Darwinian and Neo-Lamarckian factors) tends to lessen 

 the adjustability of the species to changed conditions of life. 

 The factor which has brought about mimetic resemblance is, 

 according to the theory of mimicry, selection ; as it was in my 

 letter on p. 153 not my intention to bring forth new facts, but 

 to show that one of the arguments against the theory of mimicry 

 was invalid, I had to accept selection as the factor, and accord- 

 ingly explained the excess of rarity amongst mimetic species by 

 assuming that rigorous one-sided selection makes the species 

 physiologically onesided, i.e. less fit to meet new conditions of 

 life equally well as the non-mimetic, more variable, allied 

 species, the result of which would be proportionally greater 

 scarcity of individuals or even extinction. Karl Jordan. 



Zoological Museum, Tring, August 25. 



INTERNATIONAL CONGRESS FOR THE 

 UNIFICATION OF METHODS OF TESTING. 



T N 1884 the late Prof. Bauschinger, of Munich, con- 

 ■*- ceived the idea of bringing professional men engaged 

 in testing materials into personal contact, with a view to 

 initiating researches into the physical and chemical 

 behaviour of structural materials. Congresses were held 

 at Munich, Dresden, Berlin, Vienna, and Ziirich ; and at 

 the last-named Congress it was decided to form a per- 

 manent International Association, which now numbers 

 1200 members ; and under its auspices the sixth Inter- 

 national Congress was held at Stockholm on August 23, 

 24 and 25. Prof Tetmajer, of Ziirich, presided, and 452 

 delegates from all parts of the world were present. One 

 member of each nationality represented was elected an 

 honorary president, the coinplete list being as follows : 

 Mr. .Ast (Austria), Mr. Greiner (Belgium), Prof Han- 

 nover (Denmark), Mr. Peters (Germany), Mr. Bennett 

 Brough (Great Britain), Mr. Baucke (Holland), Mr. 

 Banowitz (Hungary), Mr. Fadda (Italy), Mr. Krag 

 (Norway), Prof Belelubsky (Russia), Mr. Nyberg (Fin- 

 land), Mr. Akerman (Sweden), Mr. Schraft (Switzerland), 

 Colonel Mayandia (Spain), and Mr. C. G. Henning 

 (United States). 



The list of papers presented comprised an account of 

 the development of the iron, brick and cement industries 

 of Sweden, by Mr. A. Wahlberg ; a description of micro- 

 metallography considered as a method of testing, by Mr. 



