Al'RIL 23, I9O3J 



NA TURE 



5^3 



it without learning something new about the history 

 of the series of inventions and discoveries which have 

 culminated in Transatlantic Marconigraphy. 



Catalogue of the Collection of Palaearctic Butterflies 

 Formed by the late John Henry Leech. By Richard 

 South, F.E.S. Pp. vi + 229; portrait and two 

 coloured plates. (London : Printed by Order of the 

 Trustees of the British Museum, 1902.) 



It is very gratifying to notice how frequently, at the 

 present day, large private collections of objects of 

 natural history, when of real importance, find their 

 final resting-place in the British Museum, or in some 

 other great public collection, where their treasures 

 are available for ever, instead of being dispersed on the 

 death of the owner, and by such dispersion alone, 

 losing a large part of their scientific value, besides the 

 probability of a considerable portion being neglected, 

 and sooner or later lost or destroyed. 



Especially is this the case with great special collec- 

 tions, like that brought together by Mr. Leech, at 

 great expense, and with untiring energy and perse- 

 verance, from Lapland to Marocco and Algeria, and 

 from thence to Cashmir, and from Cashmir to Japan, 

 including the materials used in the preparation of his 

 great work on the " Butterflies of China, Japan, and 

 Corea," which is likely long to remain the standard 

 authority on the subject. A great part of these collec- 

 tions was formed by Mr. Leech himself in his 

 numerous entomological journeys, while others were 

 procured for him by enterprising collectors like Mr. 

 A. E. Pratt, in almost unknown and unexplored parts 

 of Western China and Thibet. Besides these, Mr. 

 Leech's collection includes (by purchase) the bulk of 

 the collection formed by the late Mr. Henry Pryer, 

 himself the author of the first important separate work 

 published on the butterflies of Japan, which is also 

 noticeable as having been issued in two languages, 

 English and Japanese. On the other hand, there are 

 comparatively few species and specimens from North 

 Africa and Western Siberia. 



Mr. Leech also interested himself specially in the 

 variation of species, and purchased a large selection of 

 varieties of European Lepidoptera from the collection of 

 the late Herr Miitzell, of Berlin, as well as from other 

 sources ; and as the types of new species in Mr. Leech's 

 collection have already been fully illustrated in th<- 

 works and papers published by Mr. Leech himself 

 during his lifetime, the two plates which illustrate the 

 present memorial volume are devoted to figures of some 

 of the most interesting varieties, chiefly European. 

 Every specimen in the collection is carefully enumer- 

 ated in the volume before us, the sex and exact locality 

 being carefully indicated, and all types marked. 



Entomologists owe a deep debt of gratitude to Mr. 

 Leech himself, to the liberality of his mother, and to the 

 careful work of his friend and coadjutor, Mr. South, 

 in ensuring the permanent value of this unique col- 

 lection. 



Bacteria in Daily Life. By Mrs. Percy Frankland. 

 Pp. 216. (London : Longmans, Green and Co., 

 1903.) Price 5s. net. 



Mrs. Frankland has compiled an interesting, instruc- 

 tive, and accurate account of the modern developments 

 of bacteriology. Such subjects as sewage disposal, 

 the prevention of tuberculosis, micro-organisms in 

 milk, air, and foods, which are of public importance, 

 are fully dealt with, and the modern ideas regarding 

 toxins and antitoxins are briefly discussed. No one 

 nowadays laying claim to a liberal education can dis- 

 pense with a slight knowledge, at least, of microbes 

 and their actions, and for such this work will prove 

 an adequate text-book. R. T. Hewlett. 



NO. 1747, VOL. 67] 



LETTERS TO THE EDITOR. 



[Tin' Editor does not hold himself responsible for opinions 

 expressed 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 anonymous communications.] 



A New Theory of the Tides of Terrestrial Oceans. 



In Nature of September 4, 1902 (vol. lxvi. pp. 444-445), 

 Prof. G. H. Darwin makes some criticisms upon a paper 

 of mine to which I should like to reply. 



Upon referring to pp. 537 and 624 of the paper criticised, 

 it will be seen that it aims at "rude approximations to the 

 cases found in nature," and at a " partial explanation of 

 the tides." In fact, it bears the title, " Manual of Tides, 

 Part ivA., Outlines of Tidal Theory." If, therefore, the 

 paper establishes, even in a few cases, the principal causes 

 of the tides, connecting the latter with the known tidal 

 forces, it can hardly be regarded as a " failure, " even though 

 the approximations are rather rough ; for I believe this 

 object has not been heretofore attained for any ocean tide, 

 although statements have elsewhere been made by our critic 

 which might, perhaps, lead some people to think other- 

 wise. 1 



Again, granting for the moment that the theory involved 

 in the paper is erroneous, I should still say that if observed 

 facts can be conveniently grouped by aid of it, a useful pur- 

 pose will have been subserved. In fact, the mere collection 

 of tidal data which a test of any theory implies is here, as 

 elsewhere, not without value. For instance, if our critic 

 could have had this paper before him while preparing his 

 book on tides, he would not have overlooked Berghaus's 

 invaluable cotidal chart and written " No more recent 

 attempt (than Airy's) has been made to construct such a 

 map." 2 



Prof. Darwin's principal criticisms are three in number : — 



(1) He sees no use for the equation of virtual work in 

 ascertaining the times of high water. 



(2) He thinks that the deflecting force of the earth's rota- 

 tion cannot be generally disregarded in a first approxima- 

 tion, which is all that my paper aims at. 



(3) He does not believe that ocean basins exist the free 

 periods of which are sufficiently near the tidal period to 

 account for the tides. 



(1) Concerning my application of the principle of virtual 

 work, Prof. Darwin is mistaken when he says " Mr. Harris 

 takes the displacements as proportional to the actual dis- 

 placements per unit time." What is really done is this: — 

 The magnitude of the virtual displacement (Sx, say) at any 

 given point of the system is taken to be the same for any 

 given time or hour, but varies from point to point. Since 

 the law of the oscillation of the particles is known, viz. 

 it is simply harmonic in time, and the particles throughout 

 the body are at a given instant in like or opposite phases, 

 the virtual displacement at any given point may always be 

 represented by the maximum value of the actual total dis- 

 placement at the point (cf. rule quoted in criticism). In 

 other words, if we choose to consider the small virtual dis- 

 placement as identical with a small actual displacement 

 corresponding to a time variation, the implied St will not 

 be constant for all hours. Hence the virtual displacements 

 at different hours are not simply proportional to the actual 

 displacements per unit time. He is evidently mistaken 

 when he says, " Thus all sustaining forces vanish at the 

 instant when the displacement is a maximum." Why 

 should they? Surely they generally vary in magnitude and 

 phase for the various parts of an extended oscillating body. 

 Probably the use of the rule quoted in the criticism and 

 founded upon the principle of virtual work can be most 

 readily seen when it is applied to a binodal canal-like area 

 of uniform cross section, selecting for simplicity, say, the 

 nodes as the points of application of the sustaining forces 

 ( c f- § 63). The process implied in the rule seems to be 

 correct, and, so far as I see, about as simple as it could 



1 " The Tides," p. 177, lines 2- 10. [P. 160. lines 16-23, English ed it. [ 

 thought that the passage referred to would be understood to refer to the 

 ideal case there under consideration. — G. H. D. ] 



r 2 "The Tides," p. 189, lines 10-12. [P. i7r, lines 19-21, English edit. 

 This was an oversight ; a reference to Rerghaus will be found in the forth- 

 coming article on the tides for the German ''Encyclopaedia of Mathe- 

 matics."— G. H. DJ 



