300 Notices respecting New Books. 



Erzbach*, who has done much to extend our knowledge of 

 the connection between stability of compounds on the one 

 hand, and, on the other, the volume and thermal changes 

 attending their formation. 



XXXII. Notices respecting New Books. 



Textbook of Practical Physics. By E. T. G-lazebkqok, M.A., F.B.S., 

 and W. N. Shaw, M.A. London : Longmans, Green, and Co. 

 (482 pp.). 

 r |^HE development of practical work as a necessary part of the 

 -*- teaching of science in its various branches is a very healthy 

 sign of the times, and promises well for the advantages we may 

 expect from the increased study of science which has marked the 

 last twenty years. Formerly such things as laboratories for the 

 practical study of Biology, Physics, &c. were almost unknown in 

 England, except in a few of the more advanced educational insti- 

 tutions, and Chemistry was apparently the only science thought 

 worthy of being studied practically. Now there are numerous 

 well-equipped laboratories for the practical study of Physics ; and it 

 is for the use of teachers and students in such that this book is 

 intended, and it will be welcomed by all teachers of the subject as 

 supplying a much felt want. The Authors, in marking out the 

 limits of their work, had to decide between attempting to give 

 instructions equally applicable to all the different forms of instru- 

 ments to be met with in different laboratories, which must of 

 necessity have been very vague, and adhering to the descriptions of 

 the precise instruments in use in their own laboratory ; and have 

 decided, we think very wisely, in adopting the latter course, trust- 

 ing that the necessity for adaptation to corresponding instruments 

 used elsewhere w 7 ill not seriously impair the usefulness of the book. 

 Their general aim has been to place before the reader a description 

 of a course of experiments which shah not only enable him to 

 obtain a practical acquaintance with methods of measurement, but 

 also, as far as possible, illustrate the more important principles of 

 the various subjects. There are two valuable introductory chap- 

 ters — one on the units employed and their dimensions, the other 

 on the arithmetic of numbers expressing approximate measure- 

 ments. We may quote, as an example, the application of the 

 principles of this chapter to find the effect on the value of a current, 

 as deduced from observations with the tangent-galvanometer, of an 

 error of a quarter of a degree in the reading. 

 The formula of reduction is 



C=fctaafl. 

 Suppose an error S has been made in the reading of ft, so that the 

 observed value is 



C'=& tan (0+2). 

 It is shown that when $ is less than a certain small value, this is 



* Pogg. Ann., Bcrichtc, Wied. Ann., Lieb. Ann., 1870-85. Sum- 

 marized in Meyer, Mod. Theor. d. Chan. p. 445. 



