April 12, 1900] 



NATURE 



559 



less continues, in accordance with foreign usage, to quote 

 the law Boyle discovered as " Mariotte's." He also gives 

 a fig^ue illustrating Cavendish's method of demonstrating 

 tlie law of the inverse square in electrostatics, but the 

 name of Cavendish is not mentioned, and the figure is 

 labelled " Coulomb's Law." 



It is probable that the historical motive is to be held 

 responsible for the retention of many old experiments and 

 figures of archaic apparatus. This is in many cases most 

 desirable and instructive, provided always that the later 

 developments are explained and illustrated so as to point 

 the contrast. The experiments of Wheatstone (1834) on 

 the "velocity of electricity" are of the highest interest 

 and educational value, but it is not fair to leave the 

 student with the conclusion, " Both electricities pass, then, 

 simultaneously from the coatings of the jar, and meet 

 midway between them. The velocity of propagation in 

 a copper wire was found 'to be 430,000 km. By a different 

 method .Siemens (1876) found for the velocity in an iron 

 wire 240,000 km." Again, it is certainly instructive to give 

 a figure of the early type of German mirror galvanometer 

 with a massive four-inch bar magnet inside a rectangular 

 coil, but it is a mistake to ignore the essential improve- 

 ments introduced by Thomson (Lord Kelvin), and to 

 leave the student with the impression that the instrument 

 figured is the type of a modern sensitive galvanometer. 

 Similarly, in the section on the liquefaction of gases, we 

 have an illustration of Pictet's historical apparatus (1877), 

 and we are informed that " Hydrogen was liquefied at a 

 pressure of 650 atmospheres and a temperature of- 140^ 

 On opening the tap an opaque stream of liquid of steel- 

 blue colour escaped, at the same time the solidified 

 hydrogen upon the floor produced a rattling sound as of 

 falling shot." It is stated on the previous page that the 

 critical temperature of hydrogen is - 174°. No later experi- 

 ments are mentioned. Such omissions as these can 

 hardly be justified even in the most elementary work, and 

 cannot fail to produce the impression that the book is not 

 sufficiently up to date to satisfy the requirements of 

 modern scientific education. 



In endeavouring to explain a new term, it is often con- 

 sidered necessary in elementary text-books to put the 

 idea into somewhat vague and general language, rather 

 than in the form of a precise definition, because the more 

 exact statement may fail toconvey the idea intended. We 

 are inclined to doubt the wisdom of this course, which 

 appears to be carried too far by the author. The following 

 are a few samples of the kind of statement to which we 

 refer. 



P. 24. " Work. — When a force acting on a mass sets it in 

 motion, the force is said to do work, and the result of its 

 action is called work." " In transforming forces into work 

 the question is not alone whether work is done, but also 

 in what time it is accomplished. The work done in one 

 second is called the ' effect ' of the force." 



P. 289. ^'"Equilibrium in Conductors. — When a con- 

 ductor has attained a condition of electrical equilibrium, 

 the electrical forces, and accordingly also the electrical 

 potential, are everywhere o. This merely says that in a 

 position of equilibrium, every point in and upon a con- 

 ductor has the same potential." 



P. 372. " IVheats tone's Bridge. — If the branches amb 

 SO. 1589, VOL. 61] 



and anb of the current are connected by a cross wire mn, 

 called a 'bridge,' two currents flow in opposite directions 

 in the bridge. If these currents have equal strength they 

 neutralise each other and no current passes through the 

 bridge. . ." 



P- 377-— "Edison's (1879) incandescent lamp depends 

 upon the heating action of the current. A charged filament 

 of hemp, or cotton, of high resistance {e.g. 140 ohms) and 

 bent into the form of a horseshoe, is enclosed in an ex- 

 hausted glass globe to protect the filament from burning, 

 while a current of about 100 volts passing through it 

 heats the filament to incandescence, giving it an intensity 

 of approximately fifteen candles." (Nothing more is said 

 on the subject of incandescent lamps.) 



The paragraphs " in fine print " contain the majority of 

 the formuhe, and are intended to meet the needs of 

 higher schools and colleges. They appear, however, to 

 be of too disconnected and occasional a character for the 

 purpose. A good deal of small print, e.g. three pages on 

 thunder and lightning, is of very elementary and purely 

 descriptive character. On the other hand, some rather 

 difficult points are discussed in the " coarse print," e.g. 

 the " Second proposition of the Mechanical Theory of 

 Heat. Entropy. Kinetic theory of gases." In discussing , 

 the Second Law of Thermodynamics and the Dissipation 

 of Energy, no allusion is made to reversible cycles, and 

 the information imparted is necessarily so incomplete 

 that no application could be made of it. Mayer's calcu- 

 lation of the mechanical equivalent is given, but Joule's 

 experimental verification of the assumption upon which 

 it rests is entirely ignored. It may be questioned whether 

 there is any profit in introducing such points if they cannot 

 be adequately discussed. It is not very easy to follow the 

 principle upon which the selection or omission of subjects 

 for discussion is based. The book as a whole does not 

 appear to be sufficiently definite and practical to be suited 

 for class or examination work according to English 

 standards. It is possible that it may be more suited to 

 the methods in vogue in Germany or America. 



Hugh L. Callendar. 



TWO NEW ZOOLOGICAL HANDBOOKS. 

 A Manual of Zoology. By the late Prof. T. J. Parker 



and Prof. W. A. Has well. Pp. xv -V 550. (London : 



Macmillan and Co., Ltd., 1899.) 

 An Elementary Course of Practical Zoology. By the 



late Prof. T. J. Parker and Prof. W. N. Parker. Pp. 



xii -i- 608, with 156 Illustrations. (London : Macmillan 



and Co., Ltd., 1900.) 



PROFS. PARKER AND HAS WELL have embarked 

 upon a difficult and somewhat ambitious undertaking. 

 To compress an account of practically the whole animal 

 kingdom, with 300 illustrations, into a handbook of 550 

 pages, intended for beginners, is certainly no light task at 

 the present day. Such manuals were quite possible so long 

 as it was considered sufficient for a book of this kind to 

 deal with the exteriors and the habits of animals, and to 

 consist for the greater part of illustrations of monkeys, 

 beasts and birds, while about one-fifth or less was taken 

 up by reptiles, fishes and insects, with perhaps a figure or 

 two of zoophytes or diatoms from Barbados earth. But 



