NA TURE 



[September 13, 1906 



inter se, and the association of some of these differ- 

 ences with differing seasons and climates. Many- 

 large additions exhibiting striking variations of these 

 kinds are recorded in the descriptions given of collec- 

 tions of butterflies received from South Africa, so 

 wonderfully rich in these varied forms, as well as from 

 New Zealand, the islands of the Indian Ocean, and 

 elsewhere. 



Special arrangements made at the museum for the 

 study and illustration of mimicry in various orders 

 of insects are described. All the orders receive atten- 

 tion and study there, and with such an affluence of 

 contributors from all parts of the world, with the 

 aid of the numerous willing and capable helpers to 

 whom Prof. Poulton heartily acknowledges the 

 obligations that science owes them, and with the 

 enthusiastic and intelligent interest in the subjects 

 that manifestly prevails in every department of the 

 institution, the Hope Museum is plainly pursuing 

 a career that is rendering it of great and increasing 

 scientific value. F. M. 



OUR BOOK SHELF. 

 Insect Pests of the Farm and Garden. By F. Martin- 

 Duncan. Pp. vii+143; illustrated. (Lxjndon : 

 Swan Sonnenschein and Co., Ltd.) Price 2s. bd. 

 net. 

 This little book appears in the Naturalists' Library 

 Series. It deals with a number of common insects 

 that are destructive in the field and garden, and at 

 least one rare one. The printing and illustrations are 

 good on the whole, and it is clearly and interestingly 

 written. There are, of course, printer's errors, such 

 as Brachus for Bruchus, Centorhynchus for Ceuto- 

 rhynchus, ovae for ova, &c. A few illustrations are 

 scarcely recognisable, such as that of the codling 

 moth (Fig. 38), the currant gall mite, and the goose- 

 berry red spider (the currant mite, evidently copied 

 from the Board of Agriculture leaflet, being par- 

 ticularly poor, and quite unlike the actual acarus). 



When one reads the part dealing with treatment 

 the impression is at once formed that the author is 

 not only not practically acquainted with the subject, 

 but is not au fait with any up-to-date work. No 

 mention is made of the most important insecticides, 

 &c., such as arsenate of lead, which is superseding 

 Paris green, caustic alkali wash, bisulphide of carbon, 

 &c., whilst many of the receipts given are quite out 

 of date. 



Such advice as picking up maggotty apples, the 

 cleaning of hop poles, and burning the bine, &c., will 

 scarcely meet with the approval of farmers, and is 

 certainly not necessary. One does not now see many 

 hop-poles about to clean. Nothing up to date is given 

 concerning wireworm, whilst, on the other hand, 

 people are cautioned against having animals and 

 fowls in orchards sprayed with Paris green ; the author 

 evidently knows nothing of the experiments carried 

 out which show that we can safely keep stock of all 

 kinds in the orchards even when they are actually 

 being sprayed. 



Some of the scientific names used are wrong ; that 

 of the celery fly is not Tephritis onopordinis ; the 

 names of the diamond-back moth and the red spider 

 of hops are also wrong. 



The work has evidently not been compiled from 

 sufficientlv up-to-date material to recommend it to the 

 notice of practical men, and there is nothing new in 

 it of scientific value. 



Elementary Electrical Engineering in Theory and 

 Practice. By J. H. Alexander. Pp. xii-l-208. 

 (London : Crosby Lockwood and Son, 1906.) 



It is difficult to find much in this book to recommend. 

 It is evidently not intended for the higher classes of 

 students or engineers, but this fact is scarcely 

 sufficient to warrant an entire absence of logical 

 sequence or method in the arrangement of the 

 material. The scope of the book is far too wide, 

 taking in as it does fundamental principles, measur- 

 ing instruments, electrical machinery, batteries, cables, 

 transmission, and generating stations. 



Such a wide range compressed into two hundred 

 pages must inevitably lead to a superficial grasp of 

 the subject. For instance, what can be the utility of 

 such a paragraph as the following? 



" Storage cells are always fi.xed up in a separate 

 room. Brickwork or stone, laid in cement and con- 

 crete, are used for the foundations for the machinery. 

 The coal bunkers should allow of a store of coal 

 supply for three or four weeks." 



The author would be well advised to concentrate 

 his attention on one of the sections mentioned above 

 instead of attempting to include in a single volume so 

 much that cannot adequately be treated in so small a 

 space. 



Immanuel Kants Griindlegnng zur Metaphysik der 

 Sitten. Dritte Auflage. Edited by Karl Vorlander. 

 Pp. XXX -I- 102. (Leipzig: Verlag der Diirr'schen 

 Buchhandlung, 1906.) Price 1.40 marks. 



This is the third edition of one of Kant's best-known 

 works in the excellent series of the Philosophische 

 Bibliothek. The introduction contains a well-informed 

 account of Kant's occupation with ethical subjects 

 between the years 1764 and 1785, and of the interest 

 excited by the publication of the " Grundlegung. " 

 The text is based on the best authorities, and variant 

 readings are added in the footnotes. A full index of 

 names and subjects completes the volume. 



NO. 1924, VOL. 74] 



LETTERS TO THE EDITOR. 



[The 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.] 



The Mixed Transformation of Lagrange's Equations. 



Returning to Padua after a month's absence, I read in 

 Nature of August 2 (p. 317) a letter by Mr. A. B. Basset 

 on " The Mixed Transformation of Lagrange's Equa- 

 tions." 



The letter begins : — " I should fancy from the review 

 by ' G. H. B.' in Nature of July 19 (p. 265) that the 

 papers of Prof. Levi-Civita relate largely to the mixed 

 transformation of Lagrange's equations, the complete 

 theory (Proc. Camb. Phil. Soc, vol. vi., p. 117; ' Hydro- 

 dynamics,' vol. i., p. 171) of which was first given by 

 myself so far back as 1887"; it is then shown that the 

 mixed form of Lagrange's equations may be obtained in 

 the most simple way through an elegant artifice of 

 elimination. 



The words here quoted give the impression that my 

 papers deal principally with the announced theory, and 

 that they may be little more than the reproduction of 

 some previous papers by Mr. Basset. I wish, however, the 

 readers of Nature to know — and Mr. Basset will be the 

 first to recognise the fact — that the case is quite different. 

 The papers in question (as it appears from the general 

 title, " Sur la Recherche de Solutions particulijres des 

 .Svstfemes diff^renliels et sur les Mouvements stationnaires," 

 and as it seems to me to result also from the review by 



