i6o 



NATURE 



yjan. I, 1874 



alluding to one or two of the reports of European officials, 

 which will show that, however weighty their evidence 

 may be as regards the practical side of the question, their 

 opinions in scientific matters are open to criticism. Mr. 

 Day had drawn attention to the destruction of fish by 

 various kinds of crocodiles, very properly recommending 

 that rewards should be paid for their eggs. To this one 

 of the officials rephes : — " Waging war against such fish- 

 destroying animals as crocodiles appears to me absurd. 

 I have no doubt at all but that a general destruction of 

 crocodiles would directly frustrate the end hoped for by 

 their destruction. Their very presence in numbers, it 

 being given that they live on fish, shows that the supply 

 of fish is abundant, which is all that anyone requires, and 

 nature in these matters, if left alone, keeps the balance 

 even, and resents interference." This is exactly the same 

 view as that held by the modern advocates of a general 

 preservation of birds, who would preserve even such as 

 the sparrow-hawk and cormorant, and who forget that 

 nature itself, in distributing animal life, does not always 

 consult the convenience of man. In India, the presence 

 of tigers, poisonous snakes and crocodiles, would appear 

 to prevent this doctrine from being generally adopted by 

 the European community. Another official refers to a 

 "very e.\haustive and carefully drawn up report" from a 

 Civil Surgeon in his district ; this report is accompanied 

 by a list of the freshwater fishes, in which occur some 

 species with Buchanan-flamilton designations, others 

 with Latin terms derived from a dictionary, a cod-fish, a 

 John dory, and " a very common fish, the scientific name 

 of which is supposed to be Lacerta scincus .'" Can anyone 

 doubt after this that a comprehensive and well-illustrated 

 hand-book of Indian Freshwater Fishes with an intioduc- 

 tory treatise on the elements of Ichthyology is called for? 

 Albert Gunther 



KOHLRAUSCH'S ''PHYSICAL MEASURE- 

 MENTS" 

 An Introduction to Physical Measurements, with Appen- 

 dices on Absolute Electrical Measurement, &c. By 

 Ur. F. Kohlrausch. Translated from the Second Ger- 

 man Edition by T. H. Waller, B.A., B.Sc, and H. R 

 Procter, F.C.S. (London : J. and A. Churchill, New 

 Burlington Street, 1873.) 



MESSRS. T. H. WALLER and H. R. Procter have 

 furnished us with a translation of the second 

 edition of Dr. Ko'..'rausch's "Physical Measurements," to 

 which they have a:'ded several useful Appendices and 

 Tables. 



Their work is intv iided to serve as a text-book for 

 students in experimen; 1 physics, and consists mainly of a 

 collection of the formula; used in correcting and applying 

 the results of the simpler experiments in weighing and 

 measuring, heat, light, electricity, and magnetism, accom- 

 panied in each case by such an account of the method of 

 observation employed as may suffice to render them intel- 

 ligible. 



The limits which the author assigned to himself are 

 very clearly laid down in the Translators' preface, in which 

 we are informed that " descriptions of apparatus are but 

 rarely given, as students mostly have instruments provided 

 for them," and also that " the mathematical knowledge 



required is but very elementary, as the proofs of the 

 formulae are only given when they present no complex 

 arguments," but it should perhaps have been added that, 

 even in cases where the apparatus is simple, outlines of 

 the mode of performing an experiment arc generally 

 alone supplied, the teacher being left to explain to his 

 pupils the niceties of arrangement and manipulation. 



Regarded as a syllabus of a course of physics, the book 

 is incomplete, no account, for instance, being given of 

 Favre and Silberman's Calorimeter, or, with the exception 

 of saccharimetry, of experiments on polarised light ; and 

 if the author's plan be thought to justify the exclusion of 

 these, the same reason can hardly account for the omis- 

 sion of methods for determining melting points, or the 

 specific gravity of substances whose constitution is altered 

 by exposure to the atmosphere, or the ratio of the in- 

 tensities of the illuminations produced by two sources of 

 light, or of all experiments relating to the capillary ele- 

 vation of liquids in fine tubes. 



It is, however, as a collection of formute that " Physical 

 Measurements " is likely to prove most useful, and from 

 this point of view the " Introduction " seems to us one of 

 the best parts of the book. It contains the rules for 

 finding the mean and probable errors of a set of observa- 

 tions, and for determining empirical constants by the 

 method of least squares, together with hints as to how to 

 shorten the labour often wasted in the calculation of cor- 

 rections ; points on which a short practical treatise like 

 that here provided will afford great assistance to those 

 who are not mathematicians. 



The sections devoted to weighing and measuring are 

 full and good, especially those which relate to the use of 

 the balance, but heat and light are not treated of in an 

 equally satisfactory manner. 



The experiments on these subjects which are described 

 are not numerous enough to satisfy the requirements of 

 large laboratories. Moreover, sufficient attention seems 

 scarcely to have been paid to the fact that students should 

 be encouraged to apply corrections to the results of experi- 

 ments which they perform, not so much on account of 

 the more accurate numerical values thereby obtained, as 

 for the sake of the excellent practice the necessary obser- 

 vations often afford, and the insight gained into the 

 theoretical principles on which they are founded. A case 

 in point is the omission in the article on the Deter- 

 mination of Specific Heats by the Method of Mixtures of 

 any account of the correction employed by Regnault for 

 the loss of heat by radiation. 



We miss all mention of the optical bank, and the 

 mathematical expressions for results involving the deter- 

 mination of distance in terms of differential measures on 

 that instrument. In the article on the spheromcter, which 

 is in other respects incomplete, we see no instructions for 

 finding the radius of a spherical surface too small to per- 

 mit the instrument to be placed upon it ; and omissions 

 are made in the pages devoted to the spectrometer, the 

 goniometer, and elsewhere, which combine to render the 

 section on Light very imperfect. 



Nearly one half of the book is given up to Electricity 

 and Magnetism, subjects in the study of which assistance 

 can be more readily rendered by the method of treatment 

 here adopted than in those we have been discussing, as 

 numerous mathematical formula? are required which are 



