NATURE 



[Fed. 8, 1872 



whole face of this department of entomological science 

 has undergone a wonderful change in the last twenty 

 years. 



Under these circunastances many an entomologist has 

 no doubt often \/ished thit a new " Genera of Diurnal 

 Lepidoptera " would make its appearance ; but such works 

 arc not to be lightly undertaken, and it may be long before 

 we can hope to see a good, general, systematic treatise 

 upon this group of insects. In the meanwhile we welcome 

 Mr. Kirby's catalogue as a most important aid to the study 

 of the Diurnal Lepidoptera. It is a complete catalogue 

 of the described species of the group, amounting, as an 

 estimat'',to about 9,600 in number, and gives the synonyms 

 boih of the genera and species in a clear and easily- 

 intelligible form. With the assistance thus offered to him 

 by Mr. Kirby, the intomologi^t may easily ascertain what 

 has been dune by former writers in this departmen- of hi=. 

 science, and it "ill be his o vn fault if he does not keep 

 himself rt« courant with its future progress. 



Crit cism upon a work of this nature would be out of 

 place here, and we can only cordially re:omm-nd the 

 risults of Mr. Kirbv's most conscientious labours to the 

 attention of all entomologists. 



A Class-book of Inorganic Chemistry, with Tables of 

 Chemi al Analysis, and Directions for thrir Use. By 

 D. Morris, B.A. (London: G. Phillip and Son, pp. 157.) 



This work has been compiled for the use of students pre- 

 paring for the O.x'orJ and Cambridge Mitldle Class 

 F.xaminai.ins, and the Matriculation E.xamination of the 

 Uriiversity of London ; it lays cami to no originality if 

 treatni-nt, and professes to be simply a collfction of 

 " enlarged notes," ..." ongnally culled from the 

 best modern books." Under these cir umstances we are 

 somewhat surprised that the author should have ventured 

 to publish it; we are quite unable to detect any special 

 merit in the book, and it is disfigured by many pa^sagt-s 

 which show great want of exactness. Thus, we find 

 "nitric acid, or nitric anhydride, N^O;;" "sulphate of 

 potassium or dipotassic sulphate;" the fumula of phos- 

 phate of calcium is written 3Ca3PO^, of chloiide of lime 

 CaOCf.O. We are told that ''ammonium and sodium 

 are distinguished by the smell of ammonia on the addi- 

 tion of caustic potash." " Pure water has no action upon 

 the metal (lead), but water charged with air corrodes it, 

 and the t'xide of lead thus formed dissolves in the water." 

 Among the redeeming qualities of the book may be men- 

 tioned the questions which are selected from various 

 University examination papers, and the examoles given 

 worked out in the text ; but with errors of the nature of 

 those given above it is impossible to recommend the book 

 to the student, or to regard it as a reliable source of in- 

 formation. 



Tlie Elements of Plane Geometry for the Use of Schools 

 and Colleges. By Richard P. Wright, Teacher of 

 Mathematics in University College .School, London, 

 formerly of Oueenwood College, Hampshire. With a 

 Preface by T. Archer Hirst, F.R.S., &c., late Professor 

 of Mathematics in University College, London. Second 

 Edition. (Longmans, 1 871.) 



This work would have been more correctly described as 

 being "by Eugene Rouche and Ch. de Comberousse, 

 translated and edited by Richard P. Wright," &c. But 

 although Mr Wright can lay small claim to originality, he 

 has shown judgment in the selection of an eminently 

 logical and masterly treatise on geomt-try, and he has 

 rendered it into clear and forcible English. The arr nge- 

 ment is excellent, and many of the conclusions f )r which 

 Euclid found it necessary to reason geometrically on each 

 particular case are treated generally by pur.'-ly logical 

 considerations. Many of the demonstrations, notably 

 that of the pons asinorum, are far more simple and con- 



vincing than those in Euclid. The difficulty of the twelfth 

 axiom is met by the easy axiom that through a point 

 ivithout a line only one parallel can be drawn to that line. 

 In some points there seems to be an unnecessary alteration 

 of the language of Euclid, as in the definition of a figure, 

 '■ Surfaces and Lines or combinations of them." 1 his 

 definition seems to have been introduced to enable the 

 authors to describe a locus as a figure ; but it having been 

 pointed out that a locus is not a figure, Mr. Wright has 

 described it as a line, but has not restored the word figure 

 to its ordinary acceptation. At the same time it is not 

 quite coriect to define a locus as a line, excluding such 

 loci as a pair of parallel lines, the circumference of a 

 circle with its centre, &c. Again, the word chcumference 

 is substituted for the word cncle whenever the circum- 

 ference only is intended. It is true that 'he word circle 

 in Euclid is used in two different senses, but this leads to 

 no ainb'guiry of ideas ; while the use of the word circum- 

 ferei ce lor the circumference of a circle only ex':ludes its 

 ■ip lication to an ellipse or other closed curve. The word 

 angle is not defined when first introduced, but we are told 

 afierwards that it "may be reg.irded as the quantity of 

 turning of a definite character around the veitex, which a 

 movable line must receive in p.X'rsing (rnm the direction of 

 one side to that of the other.' We fail to see the force of 

 the words " of a definite character,' amd would suggest 

 the following definition : " When a straight line moves 

 about a fixed point in its^-lf so as to occupy anew prvsiiion, 

 the quantity of turning it has undergone is called the 

 angle between the two positions." The exercises are 

 in_ enious and instructive, but those of the etrlier chapters 

 are much to > difficult for mere beginners. The treatment 

 of pioporiion is goo's, and the work as a whole is an 

 admirable introduction to the higher mathemaiics, and a 

 great help to independent investigation. We especially 

 recommend it to students who have found themselves 

 discouraged by the cumbrous form and imt a\ d'lticuiti. s 

 of Euclid. The second edition contains the alteratons 

 su!ji;ested by a la e eminent mathematician in the 

 -ithcnieiim on the appearance of the first edition, with the 

 additon of the substance of the second book of Euclid, 

 and in a lew cases the demonstrations of Euclid have 

 been restored. H. A. N. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinion r expressed 

 by his correspondents. iVo notice is taken of anonymous 

 communications. ] 



The Aurora Borealis of Feb. 4th 



After a rather long absence of auroral displays, a brilliant 

 and many coloured example was seen hfre last night, February 

 4, not quite so vivid as that of Oclober 1870, but coming next 

 to it so far as my own experience go- s. 



At about 8 P. i\l., when the maximum development was reached, 

 all the heavens were more or less covered with pink ascending 

 streamers, except towards the north, whi:h was characreris ically 

 dark and grey, first by mcan.s of a long low arch ul blackncSJ 

 transparent to lar^e stars, and then by the streamers which shot 

 up from that and along its whole length, for they were green or 

 grey only for several degrets of their height, and only became 

 pink as they neared ihe zenith, the region wkere the more 

 precise phenomena occurred, as thus : — 



1. The focus of the vertical streamers coming up from all 

 azimuths was very constant among the t-tars, but was not in the 

 zenith itself, being nearly 18° .south and 5° east thereof. 



2. The red streamers vried from orange to rose-pink, red- 

 rose, and demask-rose, or from strontium a, thrtaigh calcium a, 

 liihiUm a, and on to and be)ond po'a=siuni a, that is, tliey did 

 so to the naked eve, but the spectroscope knew no vmety of 

 reds amongst them ; and I, having a very goad referring spec- 

 trum in the lower part of the field of view, giving potassium a, 

 lithium «, sodium a, citron acetylene and green acetylene, be- 



