196 



NATURE 



[June 28, 1894 



ing the anatomy and temperament, the author considers 

 it to be essentially a stupid animal, and incapable of 

 looking after itself, though a model of patience under 

 most trying conditions. 



In mentioning the principal breeds of African camels, 

 the Maazee tribe north of Kena is omitted, also the 

 Howetat. who, though now poor and few in numbers 

 near Cairo since the railway has robbed them of the 

 carrying trade between Cairo and Suez, are still a large 

 and important tribe in the Sinai peninsula. The Kab- 

 babish tribe from the neighbourhood of Dongola, men- 

 tioned as a powerful and wealthy tribe, has, since the 

 beginning of the Mahdist movement, been practically 

 wiped out. 



The author strongly advocates the establishment of 

 stud farms to improve the breeds, as has been done by 

 the French in .-Mgeria, and then goes on to the important 

 subject of watering, strongly combating the common 

 belief that a camel does best on a small supply of water, 

 and that before a desert march they should be watered 

 at intervals, so as to train them, and to make them drink 

 the more before starting. Doubtless many errors on 

 this subject and that of feeding have sprung from infor- 

 mation obtained from Arabs, who, though skilled in 

 management, cannot always be depended on for their 

 explanations, as in the case of a Sheikh whom we heard 

 say that " a camel required less food on a hard desert 

 march than when in camp, because the stomach shrunk 

 when in work.'' Without doubt they should always start 

 on such marches in the best possible condition, and not 

 weakened by previous fasting, while, as the author points 

 out, a main reason of the .Arabs' success with their camels 

 on long and arduous marches is that they do not hurry 

 them, and afterwards graze them for da> s and even 

 weeks to recruit, a thing impracticable on service, where 

 work is at high pressure, and a large reserve of baggage 

 camels is rarely available. 



The importance of careful loading and suitable 

 saddlery is strongly insisted on, and this latter point might 

 with advantage have been gone into more fully with 

 figures of the various riding and baggage saddles in use, 

 since we have not yet got a satisfactory service pattern 

 saddle. A diagram of the camel's skeleton might also 

 have been added to the chapter on loading and march- 

 ing. Chapter iii., setting forth the author's views on 

 the instinct and intelligence of various animals, might 

 have been omitted or greatly curtailed, seeing how little 

 of it relates to the camel. 



The subject is of great importance, and, as a practical 

 work, the result of much experience, this book meets a 

 want, though reference would have been greatly facili- 

 tated by an index. 



Modern Plane Geometry. IJy G. Richardson, M.A.,and 

 A. S. Ramsey, M.A. (London : Macmillan and Co., 

 1894.) 



A CLOSK examination of this small treatise shows at 

 a glance that the usual method of treatment has under- 

 gone considerable alteration. The proofs contained 

 therein are of those theorems in the syllabus of modern 

 plane geometry which was issued by the Association for 

 the Improvement of Geometrical Teaching. The range 

 of the subject treated may be gathered to a certain extent 

 from the statement that the work is intended to serve as 

 a sequel to Euclid, or to the "Treatise on Klementary 

 Plane (geometry" issued by the above-mentioned Asso- 

 ciation, and, as the authors state, as a systematic means 

 of procedure from Euclidean geometry to the higher 

 descriptive geometry of conies and of imaginary 

 points. The chapters treat of the geometry of the 

 triangle, quadrangle and circle, harmonic ratio, geo- 

 metrical maxima and minima, that relating to the first 

 being fully considered and containing an introduction 

 to more recent work on special points connected with 



NO. 12S7, VOL. 50] 



the triangle. Other chapters deal with cross ratios, 

 involution and reciprocal polars, and projection. The 

 authors inform us that there has been practically no 

 departure from the syllabus referred to above, with' the 

 exception of a few additions and the interpolated 

 examples and problems. The theorems are for the most 

 part accompanied by clearly drawn figures which 

 considerably facilit.ite the rendering of the text. 



A little familiarity with this treatise will commend it 

 to many of our readers, for the authors are clear and 

 concise in their treatment of the theorems with which 

 they have dealt. 



Chemistry Demonstration Sheets. (London: Blackieand 

 Son, 1894.) 



In our opinion, the series of diagrammatic sketches of 

 chemical apparatus just published by Messrs. Blackie 

 may be put to extremely harmful use. " The sheets have 

 been designed,'' say the publishers, " as a lecture-room 

 aid in the teaching of chemistry. They present, drawn 

 in bold outline, the apparatus used in the experiments of 

 a first course, and underneath each diagram is set down 

 the chemical formula of the experiment. The diagrams 

 are drawn in elevation, and are just what a student re- 

 quires to sketch in the examination room, while the 

 formuUtt, being constantly before the eye along with the 

 diagrams, will become indelibly imprinted on the 

 memory." If the sheets are merely used to describe the 

 arrangement of apparatus for experiments actually per- 

 formed, no one will, of course, object to them. Hut il 

 (and this is more likely) the sheets are employed to im- 

 press upon the student's memory chemical reactions and 

 apparatus never seen in reality, they could not be con- 

 demned too strongly. Teachers are often too glad to 

 avoid experimentation and to refer their classes to text- j 

 books for descriptions of chemical changes brought about 

 by various means. Messrs. lilackie's wall sheets will 

 facilitate such a shirking of responsibility. 



LETTERS TO THE EDITOR. 



[ 1 he Editor dots not hoid himselj responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertaii 

 to return, or to correspond ••uith the writers of, rejected 

 manuscripts intended for this or any other part <?/ NATURE. 

 No notice is taken ol anonymous communications.] 



Panmixia and Natural Selection. 



Mr. Wkldon's letter on this subject, in Nature of May j, 

 calls, I think, fora few further observ.itions. He tirst criticises 

 the statement that "the survival-mean must, on cessntion of 

 selection, fall to the birth-mean," by showing that there are 

 probably cases in nature in which the surviv.il and birllime.ins 

 may coincide, owing to the removal by selection of all in- 

 dividuals ahove and iielow the mean, they being approximately 

 equal in number. This is, no doubt, the c.ise with certain 

 characters of a species, but probably never with all or even with 

 most characters. Darwin states that in France and Ciermany 

 while pigeons are killed off by kites, and that on the coast of 

 Ireland black fowls are also killed off by sea-eagles. These 

 and other analogous facts render it probable that in many 

 species of animals colour is kept to the inconspicuous and pro- 

 tective mean tint by the elimination of all individuals which 

 vary much on cither side of it, and thus, as regards colour, the 

 birlhmean and the survival mean may be almost identical, liul 

 with many other characters this is not the case. In sbccp, 

 cattle, and horses it has been observed that when the larger low- 

 land breeds are taken to bleak mountain regions they gradually 

 dwindle in size, only the smaller and hardier of each gencialion 

 surviving the severe winter and spring climate and the compara- 

 tively innutritious food. Here the elimination is clearly in one 

 main direction ; and the absence of this selection due to the 

 transference of the whole body of such reduced individuals to a 

 milder climale and belter pastures, would no doubt lead to a 

 slight increase of average size, indicating that the birth-mean had 

 been above the survival-mean. .So also in the case of the half- 



