September 20, 1894J 



NA TURE 



497 



ihered to throughout. Sometimes centimetres are 



:iiployed, and sometimes millimetres. This is of no 



insequence, except so far as it tends to keep alive and 



propagate the state of confusion from which the C.G.S. 



\ stem might hive been expected to deliver the scientific 



. irld. 



The first part of the book deals with the mechanics of 

 Milids, liquids, and gases. The usual methods of measur- 

 .; lengths, &c., are described, and an account is 

 en of experiments on the balance, on the laws of the 

 pendulum, on elasticity, and on acoustics. The greater 

 portion of the space is devoted to experiments with liquids 

 ■ l gases. The full account which is given of the 

 ■ihods of making measurements of a mechanical nature 

 in matter in these two states, should be very useful to 

 le students for which the book is designed. 

 The second division, which is devoted to heat, is 

 :ellent. A large number of experiments are described, 

 )st of them of great importance to the modern chemist. 

 In this connection may be mentioned specially th>; sec- 

 tions dealing with melting points, the effect of dissolved 

 substances on the freezing and boiling points of liquids, 

 and the amount of heat evolved in solution and chemical 

 oinbination. .A. section is devoted to the determination 

 "f the mechanical equivalent of heat by the aid of what 

 - practically a model of Joule's apparatus. 



Optical measurements and observations occupy the 



next portion. Some simple experiments with rerlecting 



j surfaces, lenses, and prisms are given, so as to form an 



I introduction to the subject. A few simple experiments 



with combinations of lenses with lenses or mirrors would 



!i ne been of much use here, for students generally find 



iculty with such experiments, and require some little 



jierience before they can deal practically with the real 



11 virtual images which are seen in mid-space, and not 



u n the tube of a telescope. .\ large part of the section 



devoted to spectrum analysis, and there are some 



client plates of emission and absorption spectral. A 



Tt account of the phenomena of polarisation leads up 



to a chapter on the rotation of the plane of polarisation 



bv various substances, and the use of this property for 



charimetry and other purposes. 



The last division of the book, which is devoted to 

 electricity and magnetism, is somewhat abbreviated, 

 only those parts of the subject being included which are 

 supposed to be of interest to the chemist. Voltaic elec- 

 tricity practically tikes up the whole of the space. The 

 same omission of definitions, which has been already 

 noticed, shows itself strongly here, no definition being 

 given of either the ampere, the volt, or the ohm, while 

 the enunciation of Ohm's Law is just what a schoolboy 

 might be expected to put down. Although a tangent 

 galvanometer is described, no hint is given that it is 

 possible to calculate its " reduction factor " if the value 

 of " H " is known, and, in fact, the electromagnetic defini- 

 tions of the units seem quite kept out of sight. From a 

 physical point of view, this division compares C[uite un- 

 favourably with the three other divisions. 



The volume is brought to a conclusion by a useful 

 collection of numerical tables, physical and mathe- 

 matical. 



In spite of the defectswhich have seemed to call for 

 notice, the book is undoubtedly a useful one, the defects 



NO 12Q9, VOL. 50 



I 



being such as the teacher can very easily remove. 

 \{ a third edition is called for, it is to be hoped that the 

 authors may see their way themselves to remove them. 



The book will often be of service to those teachers 

 who are engaged in the task of conducting classes in 

 practical physics, for it will often suggest fresh experi- 

 ments to be added to those forming the regular course 

 of the laboratory. But it must be remembered that 

 although a demonstrator in the course of a few years 

 may acquire a knowledge of a large number of experi- 

 mental methods, yet the students who come under his 

 care for a year or so have only time to acquire a very 

 limited acquaintance with the subject, so that if a new 

 experiment is added to the course, it practically dis- 

 places some old one. The course of experiments which 

 is most suitable for students of a particular type working 

 for a particular end, very soon settles itself by a process 

 of selection, and then must remain practically unchanged, 

 although there may be a gradual evolution in the em- 

 ployment of improved methods. 



G. F. C. Searle. 



OUR BOOK SHELF. 



Object Lessons in Elenuntary Science. By Vincent T. 

 Murche. Three volumes. (London : Macmillan and 

 Co., 1S94.) 



When a child is shown any object, he usually asks 

 '•What is it.'" and then "What does it do.'" If these 

 questions are sensibly answered the child learns much 

 about the properties of common things while he is very 

 young, and, what is more, his faculty of observation is 

 developed. Evidently, then, an excellent grounding for 

 a scientific education can be obtained from object lessons. 

 Simple objects are brought under the children's notice, 

 and their peculiarities observed. For instance, liquids 

 such as water, oil, wine, milk, and quicksilver are taken 

 and used to show that they flow, break up into drop?, 

 have no shape of their own, and keep a level surface. 

 Physical properties of solids can then be treated ; btt 

 whatever the subject of the object lesson, the aim of the 

 teacher must be to let the class come to their own con- 

 clusions upon the points illustrated. This principle of 

 sound instruction is well exemplified by the lesson on 

 hard and soft bodies in the first of the three volumes 

 before us. The aim of the lesson is to enable a child to 

 express clearly (i) what he understands by " hard ' and 

 " soft " ; (2) that hardness and softness are merely rela- 

 tive terms ; (3) how to test the hardness of a body. Such 

 objects as an apple, a turnip, a potato, cork, chalk, wood, 

 lead, iron,llint, steel and glass are taken, and children 

 are asked to scratch them with the finger-nail. It is then 

 found that some of the objects can be scratched easily, 

 ethers not so easily ; a third class can only be scratched 

 with difficulty, and a fourth cannot be marked at all with 

 the finger-nail. The experiments are afterwards repeated 

 with a knife, and then the objects are rubbed against one 

 another, and the results noticed. By these means the 

 pupils learn that there are many degrees of hardness, 

 some bodies which are commonly called hard being 

 really soft when compared with others; t-.i,' lead is hard 

 when compared with wood, but soft when compared with 

 iron, and so on. To our minds, this method of teaching 

 elementary science is admirable. It inust not be supposed 

 however, that Mr. Murchc only deals with physical con- 

 ditions. His excellent little volumes are also concerned 

 with the chemistry of common things, with the mechanics 

 of every-day life, with zoology, botany, and physiology, 

 and with various arts and manufactures. The volumes 

 loUow a scheme of object teaching in elementary science 



