172 



NA rURE 



[December 26, 1895 



wishing to study any of the subjects dealt with in this 

 " Encyclopaedia of Technical Education." The treatment 

 is thorough, the illustrations numerous, and the printing 

 good. N. J. L. 



OUR BOOK SHELF. 

 A Laboratory Course in Experitnental Physics. By 

 W. J. Loudon, B.A., Demonstrator in Physics in the 

 University of Toronto, and J. C. McLennan, B.A., 

 Assistant Demonstrator in Physics in the University 

 of Toronto. Pp. vi + 302. (New York and London : 

 Macmillan and Co., 1895.) 

 This book, the authors tell us in the preface, is the out- 

 come of their own experience, and is intended, in the 

 first instance, to be used by the students at the University 

 of Toronto, and the hope is expressed that it will be 

 appreciated by those engaged in teaching experimental 

 physics elsewhere. 



The book is divided into two parts. Part i. is devoted 

 to the description of elementary apparatus and elementary 

 methods of performing simple experiments in mechanics, 

 light, photometry, and heat. In this part students are only 

 expected to be acquainted with the elements of algebra 

 and trigonometry. On p. 55 is given a very neat element- 

 ary proof of the fact that the deviation of a ray of light 

 passing through a prism is a minimum when its direction 

 is symmetrical with respect to the refracting surfaces. 

 We think that, considering how elementary this part is, 

 the explanations might at times be simpler. It is not 

 wise to indulge too frequently in such expressions as 

 " it can be readily seen," even in matter intended for 

 advanced students ; and teachers cannot be too lucid 

 when dealing with beginners. 



Part ii. is intended for advanced students, and contains 

 directions for experiments in acoustics, heat, electricity, 

 and magnetism, with an appendix on the determination 

 of gravity and on the torsion pendulum. The theory of 

 the various experiments is given, and demands a wider 

 mathematical knowledge, e.g. the laws of the transverse 

 vibrations of strings are deduced from the equations of 

 motion. A striking omission in this part is the little 

 attention which is given to the corrections which have 

 to be applied when making most accurate physical 

 measurements. 



The choice of experiments is good, the theory and 

 descriptions of the apparatus are accurate, and the 

 illustrations are clear. The division into elementary and 

 advanced is not apt, as many of the experiments in 

 Part ii. would be more suitably placed in Part i. This, 

 however, is not a serious defect, as teachers using the 

 book can arrange the order of the experiments to suit 

 themselves. We certainly think that students of physics 

 should become acquainted with the simpler electrical 

 experiments as early as possible. 



The book is well got up, and its value is greatly en- 

 hanced by the tables of physical constants at the end. 

 We heartily recommend the work to teachers of practical 

 physics as containing very good matter, and being accurate 

 and free from misprints. W. G. Rhodes. 



The Natural History of ''^ Eristalis tenax" or the Drone- 

 fly. By G. B. Buckton, F.R.S. Pp. iv + 92. With 

 illustrations. (London : Macmillan and Co., 1895.) 

 The author's solid contributions to more than one branch 

 of science may well protect him from criticism of extreme 

 severity, but it is our duty to remark that this is not an 

 adequate account of the drone-fly. The subject is a 

 particularly good one. The drone-fly is very common, 

 large for a dipterous insect, and distinguished by many 

 interesting peculiarities of structure and habit. But the 

 author has not realised how much work goes to the pro- 

 duction of an exact and thorough monograph. Such a 

 monograph demands minute investigation of the anatomy 



NO. 1365, VOL. 53I 



of every stage, comparison with some few allies at leasts 

 and much patient observation of the living insect. Mr. 

 Buckton has not worked out the anatomy of the drone- 

 fly in any stage, as the vague figures testify. Some im- 

 portant and very peculiar features of the larva are passed 

 over without mention. There is no effective comparison 

 with other insects. The habits of the larva and the fly 

 have been attended to, and the account of the mode of 

 life of the fly contains the only valuable facts in the book. 

 There is much matter concerning insects in general, but 

 this is not always either trustworthy or pertinent. Some- 

 times facts and theories are cited, not from the original 

 memoirs, but from any author who happened to be at 

 hand. Weismann on Corethra is quoted from Balfour,. 

 Johnston on Culex from Riley, Miiller on mosaic vision 

 from Mallock. The danger of this practice is illustrated 

 by the last case, where Mr. Buckton shows that he is 

 not fully possessed of the theory of mosaic vision. It 

 may be useful to remark that the larvie and egg-chains 

 mentioned on page 19 probably belong to the very 

 familiar Chironomus. The drone-fly has been studied 

 by our author as a hobby, and he has no doubt got much 

 pleasure out of it ; but a more serious attack should be 

 made upon it before long. L. C. M. 



Working Models for Engineering Students. Engine Slide- 

 Valves. Designed by Messrs. T. Jones, M.I.Mech.E.,. 

 and T. G. Jones, B.Sc. Second edition. (Manchester : 

 John Heywood, 1895.) 

 To obtain a thorough insight into the movements of 

 slide-valves, and to completely understand the distribu- 

 tion of steam, is generally a difficult matter to first-year 

 students and engineering apprentices. These models,, 

 however, should greatly assist all who study the subject :. 

 they are neatly printed on cardboard, the important parts 

 are sectioned and tinted, and the valves are movable so- 

 as to show their positions when the piston is at any part 

 of the stroke. The relative positions of crank-pins and 

 eccentrics are clearly shown, as well as the valves and 

 steam-ports. The models are of a convenient size, being 

 six inches long by four inches wide, and they represent 

 eight different kinds of slide-valves. As such models 

 must be absolutely accurate from a mechanical point of 

 view to be of use to technical students, we must point 

 out that No. I is said to represent a slide-valve common 

 in locomotive practice ; but the valve spindle is shown 

 passing through the valve, whereas valve buckles are 

 always used. No. 2 is a single-acting piston valve for a 

 steam hammer. If it is considered necessary in this case 

 to show the piston and rod, why not do it accurately ? 

 The parts shown do not represent a steam-hammer piston 

 and part of the rod. 



Model No. 5 represents a partly-balanced ordinary 

 slide-valve. The authors omit to say that the space 

 inside the relief ring must be open to the exhaust cavity 

 to allow any steam leaking past the ring to escape, other- 

 wise'it would be of no good. This type of valve is now- 

 being largely used for locomotive purposes. The same 

 defect is to be found in model No. 7. 



Taken as a whole, the models are very useful for the 

 purpose of illustration ; they will be of much value to 

 students and others interested in the subject. 

 Macmillan's Geography Readers. Book vii. Pp. 240.. 



(London : Macmillan and Co., 1895). 

 In this little Reader for elementary schools, instructive 

 descriptions are given of the chief places and objects 

 of interest to be seen in a journey through the United 

 States ; and the main historical facts concerning the 

 New World are woven into the lessons, to give them 

 additional brightness. The book also contains sections 

 on ocean currents and tides, and is well illustrated ; while 

 the numerous extracts from the writings of travellers, 

 give a good idea of the conditions and characteristics of 

 American people. 



