196 



NA TURE 



[December 29, i8q8 



the present day. As examples we would point especially 

 to his master!)' accounts of Ptypdactylus hassctqtiislii 

 and Chahides ocellatus, which may be recom iiended for 

 study to any who should still doubt the derivation of 

 what are called species, or who, unable to devote them- 

 selves to original investigation of this kind, and in- 

 fluenced by statements of ignorant or prejudiced writers, 

 persist in looking upon species as definite units in nature. 

 In these examples we see how forms that are so different 

 in their extremes, in size, scaling, and coloration com- 

 bined, that one would unreservedly refer them to distinct 

 species, are connected by such insensible gradations 

 that it is with the greatest difficulty, and only by drawing 

 arbitrary limits, that we are able to break up the series 

 into a number of varieties ; and how these chains of 

 varieties correspond with the direction of definite lines 

 of geographical distribution. In order to render the 

 degree of individual variations more readily intelligible, 

 long lists of measurements and tabulations of details of 

 lepidosis are appended ; these tables will prove of lasting 

 value, from the care and completeness with which they 

 have been drawn up. 



It is only to be regretted that this exhaustive treatment 

 of variations outside the limited range of Egypt has not 

 been carried out through the whole work, as it would 

 have yielded highly interesting results in the case of 

 Latastia longicaudata, Eumeces schncideri, Mabiiia 

 quinquetaeniata^ Naia nigricollis, and Bufo regularis. 

 In fact, a little inconsistency in the general plan — some 

 families being characterised whilst others are not — to- 

 gether with the omission of anatomical details which an 

 author so well qualified to deal with these matters might 

 have been expected to furnish, are among the few defects 

 we notice in this admirable work. 



The coloured plates, forty in number, mostly the work 

 of Mr. P. J. Smit, equal, if some do not even surpass, 

 the best that have ever been published of a group of 

 animals particularly difficult to depict in life-like attitudes. 

 We would specially commend, as high examples of 

 artistic skill combined with scrupulous attention to 

 details, pis. xiv. {Uromastix aegyp/ius), xxix. {Chaiuaeleon 

 vulgaris), and xxxviii. {Zamenis diademd). Numerous 

 black plates and figures in the text, drawn by Messrs. J. 

 Green, Smit, and Groenvold, complete the illustrations, 

 one specimen at least of every species known from the 

 area dealt with being represented. 



The introduction, dealing with the physical features of 

 the region, is illustrated by a series of exceedingly beau- 

 tiful photographs in electrotype, as well as by a map 

 showing all the localities whence the specimens described 

 were obtained. 



Appearing at the moment when the whole nation is 

 rejoicing over the re-establishment of Anglo-Egyptian 

 rule beyond the limits of Egypt proper, this first instal- 

 ment of a work on a fauna too much neglected since the 

 days of the famous French expedition, will be especially 

 welcome. It is therefore to be regretted, in view of the 

 increased interest which will no doubt henceforth be 

 taken in the natural history of Egypt, that the small 

 number of the issue — loo copies only — will render the 

 circulation of the book more limited than it deserves. 

 G. A. BOULENGER. 

 NO. 1522, VOL. 59] 



A BOOK WITH TWO NAMES. 

 Quick and Easy Methods of Calculating. A Simph 

 E.vplanation of the Theory and Use of the Slide-Rule 

 Logarithms, S^c. With numerous Examples workec 

 out by Robert Gordon Blaine, M.E , Assoc. M. Inst. C.E. 

 &c. (London : E. and F.N. Spon, Ltd. New York 

 Spon and Chamberlain, i8g8.) 



THE author makes his title, " Quick and Easy Methods 

 of Calculating" — at least, that is all that is in large 

 print on the title-page ; but the binder calls it, on the out- 

 side of the book, " The Slide-Rule." The binder is right. 

 The author gives a very short account of some methods 

 of shortened arithmetic, in which he points out that it is 

 unnecessary to work out the results of an observation witli 

 very great or unlimited accuracy when the observatior> 

 itself is subject to well-known possible errors. He 

 might have traced the connection between the desired 

 accuracy of the arithmetic and the probable accuracy 

 of the observation as dependant on its form, but 

 he has not. There is a simple non-algebraical and 

 very clear explanation of logarithms : then the real 

 object of the book, an explanation of the sliderule> 

 follows. As in all explanations of the slide-rule that 

 are published, however clear and obvious they may be 

 to the user of the slide-rule, there is, of necessity per 

 haps, such an amount of detail and of rule as to possibh 

 scare any would-be user of this invaluable instrument 

 with the fear that he could not hope to remember it all 

 The writer of this notice has always felt that this difficult) 

 can only be overcome by half an hour's personal explan- 

 ation, in which case a book becomes unnecessary ; how-l 

 ever, for those who cannot meet with this personall 

 assistance, the little book before us is clear, logical and' 

 accurate. A great number of examples, mainly derived 

 from the engineering laboratory, are given, which serve 

 both to show the great scope of the slide-rule and as 

 exercises in its use. 



By way of criticism, the writer would point out that 

 to find cube roots it is preferable to use the slide in- 

 verted to set I on C against the cube on A, and find at 

 what part of U and D identical readings face each other. 

 Any reading except 1 can be found twice on A, and three 

 places on 51 and I) can be found for the cube roots of n 

 10// and ICO//. The rule that the writer has always given 

 in order to know where to read is as follows : if the cube 

 has I (4, 7, Sec.) digits the cube root will be found on D to 

 the left of the left possible setting on A. If it has 2 (s, 

 8, &c.) digits the cube root will be found on D between 

 the possible settings on A, and if 3 (6, 9, &c.) it will be 

 found on I) to the right of the right setting on A. This 

 very simjilL- rule has the advantage of never failing. Un- 

 fortunately the rule, as given by the author for the less 

 convenient method with the slide not inverted, does not 

 answer, except by chance, for the example he himself 

 gives to illustrate it ; for, according to this rule, v'f'3S 

 = 8'6 + (as given without the + by the author) or = 1855, 

 but this is really = ^i'^'jS. 



The writer has always felt that though rules for the 

 number of digits may be worth formulating, they are not 

 worth using or remembering ; also that the memory is 

 needlessly taxed by any system of instruction such as is 



