146 



NA TURE 



[June 14, 1888 



There is one drawback in a work of this kind, and to 

 some extent it is perhaps unavoidable. Mr. Saunders, 

 following literally the scheme originally laid before him, 

 and disregarding the exceptions therein provided for, de- 

 votes two pages to each species of bird. Now it is evident 

 that this Procrustean plan cuts off many details of the 

 greatest interest from what might be said of some species, 

 and compels the story of comparatively uninteresting 

 species to be stretched out. Among these last must of 

 course be reckoned those which have only a few times 

 made their way to the British Islands, and have scarcely 

 a claim to be called " British " birds. In a work like this, 

 Mr. Saunders, with the justly-earned reputation he pos- 

 sesses, might well have taken a new departure ; but, 

 unfortunately, four out of the twenty species included in 

 his first part come under this condemnation. Their room, 

 where every line is precious, would have been better than 

 their company, and their introduction gives the beginner 

 a wholly mistaken notion of the British fau na. Figures 

 of the same absolute dimensions are often useful for 

 certain purposes of comparison ; but to treat the Rock- 

 Thrush and three exotic species of Wheatears on an equality 

 with our real denizens, that have inhabited these islands 

 longer probably than any human beings, is to present a 

 piece of distorted perspective. The practice was excus- 

 able in old days, and those that had to tread the ancient 

 tracks were compelled to follow it ; but here was an op- 

 portunity of striking out a fresh line. Of course there is 

 great difficulty in drawing that line, for it must be drawn 

 arbitrarily, but an arbitary line would be better than 

 none. On a wharf a post-and-rail fence, or a suspended 

 chain, may be placed almost at random, and people may 

 say that it should have been a few inches nearer to, or 

 further from, the brink, but if it saves them from falling 

 into the water, few persons will not recognize the service 

 it does. 



It is a pity that almost the first word in this excellent 

 book is one to which exception must be taken. Mr. 

 Saunders has brought back the vulgar name of " Missel- 

 Thrush," which some people fondly hoped had been for 

 ever abrogated — as being either a corrupt abbreviation or 

 wholly without meaning. Of course he can cite Willughby 

 and a long string of subsequent authorities in his favour ; but 

 the " auctorttm plurimorum" principle is directly opposed 

 to sound scientific sense ; and if Mr. Saunders will look 

 up Willughby's predecessors — Charleton and Merrett — he 

 will find that they do not admit the solecism. In a work of 

 this kind, which cannot fail to have a great effect upon 

 the rising generation of ornithologists, the least tendency 

 to return to exploded errors is to be deplored. So much 

 for criticism of the part which is now before me : I gladly 

 say of the whole book — Floreat. Alfred Newton. 



THEORY AND USE OF A PHYSICAL 

 BALANCE. 

 Theory and Use of a Physical Balance. By James Walker, 

 M.A., Demonstrator at the Clarendon Laboratory. 

 (Oxford : Clarendon Press, 1887.) 



THE author states that this publication was originally 

 intended as a chapter of a book on practical 

 physics for the use of students at the Clarendon Labora- 

 tory, but that he proposes to publish each chapter 



when ready, without waiting for the completion of the 

 work. This method certainly has some advantages 

 both from the author's and the student's points of view. 

 The practical study of physics, like that of all other 

 sciences, and perhaps even to a greater extent than any 

 other, is rapidly becoming specialized, with the necessary 

 consequences that while each subdivision is expanding 

 and becoming weighted with more details and technic- 

 alities, many diligent workers on one part of the subject 

 are indifferent to the methods and appliances used in 

 other branches. The numerous army of students in 

 electricity and magnetism may take, for example, but a 

 very superficial interest in the experimental side of 

 acoustics or optics. At the same time it may be open 

 to question whether it is advisable to break a work up 

 into comparatively small fragments, as appears to be 

 the intention in the present case. Like all other matter, 

 the subject may lose in cohesion by being presented in 

 too fine a state of division. 



The instalment now issued gives a detailed and precise 

 description of one of Oertling's balances used in the 

 Clarendon Laboratory. The very clear explanation of 

 the mechanism is assisted by three plates, one a photo- 

 graph showing a general view, and the others line 

 drawings of the various parts. Any want of clearness and 

 definition in the photograph, which is not a particularly 

 happy example of a collotype, is amply atoned for in the 

 sectional diagrams. 



Details are given of the methods adopted by the 

 manufacturers to insure the accurate adjustment of the 

 knife-edges, to test for their parallelism, for their being in 

 the same plane, for the equality of the lengths of the arms, 

 and of the masses of the pans, &c. The expression for 

 the sensibility of the balance is determined from the 

 general equations of equilibrium, and practical instruc- 

 tions are given with the necessary formulae for performing 

 some half-dozen of the usual physical operations with 

 the balance, such as the determination of density of 

 bodies heavier and lighter than water, of bodies in small 

 pieces, &c. 



In a thorough and somewhat elaborate investigation, 

 which seems hardly suitable for a work intended as a hand- 

 book for a student entering on a course of laboratory in- 

 struction, the writer discusses the equations of motion of a 

 balance, and shows that the method of determining the 

 position of equilibrium from the amplitude of the oscilla- 

 tions on either side of the zero is not rigidly correct, since 

 the beam with its adjuncts have not a simple definite 

 period of vibration like a pendulum. The reassuring 

 result is, however, arrived at, that the errors introduced 

 are of a vanishing order, if the masses in the pans remain 

 constant during a set of weighings. 



Borda's method of counterpoising to eliminate errors 

 of the instrument is recommended according to the usual 

 practice, a mass heavier than the substance to be weighed 

 being placed in the left-hand pan, while the substance 

 and known masses are placed in the right-hand pan to 

 bring the beam into an observed position of equilibrium. 

 This procedure has advantages over the more tedious 

 and less cleanly plan of exactly counterbalancing the 

 substance with shot and fine sand, &c. 



In allowing for the supporting force of the atmosphere, 

 the author assumes that the average amount of moisture in 



II 



