2 lO 



NATURE 



[August 17, 1911 



sits in a Hying machine which makes its way through 

 the air ' fly '? If so, the swift and the merlin and 

 eagle have an action for which we should find an- 

 other name. One thing such acts have in common — 

 progress. They have little else." 



Mr. Dewar says truly that though no date in a 

 calendar can end or begin winter, yet there are some 

 natural events — small touches, but sure — that end one 

 season and begin another. One of them is the nest — 

 with the eggs — of the earliest song-thrush. "The 

 nest may be set in a winter hedge, and a return of 

 iron days and nights kill the work and prevent other 

 thrushes starting on their nests for weeks to come. 

 It does not signify. The first thrush nest found in 

 March in the thorn or ivy, the clay dried, the eggs 

 laid, ended winter." But he does not do the fly- 

 catcher justice when he says it can squeak, and has 

 besides a fretful monosyllable or so, and there is his 

 music. It is true that the fly-catcher very rarelv sings, 

 and that many people have apparently never heard 

 the song ; but it does really sing occasionally for all 

 that. How one wrong letter will alter the look of 

 a sentence, and even puzzle the reader for a moment ! 

 We notice "swallow" written for "sallow" in one 

 place, and "root" for "rook" in another. 



TEXT-BOOKS OF PHYSICS. 



(1) Mechanics and Heat : a Text-book for Colleges and 

 Technical Schools. By W. S. Franklin and Barry 

 Macnutt. Pp. x + 409. (New York : The Macmillan 

 Co.; London: Macmillan and Co., Ltd., 1910.) 

 Price ~s. 6d. 



(2) ,1 Text-book of Physics. By H. E, Hurst and 

 R. T. Lattey. Pp. x + 638. (London: Constable 

 and Co., Ltd., 1910.) Price 8s. 6d. net. 



(1) \1 HTHIN the last half-century much experi- 

 » * ence has been gained as to the methods 

 which can be used most profitably in the teaching 

 of science ; nevertheless, there is still much diversity 

 of opinion as to the best method to be used. Fol- 

 lowers of the heuristic school maintain that a student 

 should build up his knowledge of science by his own 

 unaided exertions, the function of a teacher being to 

 guide the student's mind insidiously toward the cor- 

 rect path. Has anj teacher ever attempted to proceed 

 severely on these lines? It may be doubted. So far 

 as the teaching of physics is concerned, such an 

 attempt would be so ridiculously futile that no one 

 could have made it seriously. Ideas such as those 

 connoted by the words "energy," "potential," " en- 

 ' tropy." and a host of similar expressions could scarcely 

 be derived by any student, even if he were of the 

 type that might develop subsequently into a Kelvin or 

 a Rayleigh. Quite apart, however, from the question 

 of possibility, it may be argued that no student has 

 received a satisfactory training unless he has learned 

 to profit by the knowledge which has been accumu- 

 lated by others. Dismissing, then, the claims of the 

 heuristic system as enunciated by its most rigid ad- 

 herents, the question arises, To what extent is a 

 student necessarily dependent on personal observation, 

 and to what extent is it profitable for him to imbibe 

 ideas directly from his teacher? Xo general answer 

 2 1 8l, VOL. 87 1 



can be given to this question, since so much must 

 depend on the personalities of both the student and 

 the teacher; but if it be accepted that science is the 

 study oi real phenomena, it must follow that the 

 practical work done by the student must be sufficiently 

 extensive to give him a clear idea of the phenomena 

 which he investigates. Not only the nature of the 

 experiments, but the order in which they are per- 

 formed, is of importance. Most of the difficulty ex- 

 perienced by students in becoming acquainted with 

 tlie dynamical properties of solids and fluids is due 

 to the practice of studying the laws of statics ex- 

 haustively before the laws of motion have been mas- 

 tered ; much of the time now spent in the experimental 

 studv of statics might be devoted with advantage to 

 the performance of simple experiments designed to 

 illustrate the laws of dynamics. In a systematic 

 course of study an accurate and comprehensive know- 

 ledge of mechanical principles should be gained as 

 early as possible, for most of the exact sciences can- 

 not be mastered without such a knowledge. 



Messrs. Franklin and Macnutt have advisedly de- 

 voted the first 269 pages of their text-book to the 

 study of the mechanical properties of solids and fluids ; 

 such subjects as virtual work, the properties of 

 rotating bodies (including the gyrostat), the analysis 

 of the stresses called into play by straining an elastic 

 substance, and the fundamental laws of hydro- 

 dvnamics are dealt with in a simple but illuminating 

 manner. A few errors may be noticed. The action 

 of the Pitot tube cannot be deduced from the force 

 exerted by a jet of liquid impinging normally on a 

 plane. The velocity of stream, as measured by a Pitot 

 tube, should be equal to >j2gh, where h is the height 

 at which the liquid stands in the tube, instead of v gh, 

 as given on p. 260. The depression of the surface 

 of the water escaping from the central outlet of a 

 laboratory basin is not essentially due to rotation of 

 the water; even when the water approaches the outlet 

 radially its velocity must increase and its pressure 

 must diminish. In general, however, the treatment of 

 the subject is excellent, and the student is afforded an 

 opportunity of becoming acquainted with many in- 

 teresting phenomena connected with engineering prac- 

 tice, which are not generally mentioned in books de- 

 voted I" the theory of mechanics. 



The second part of the book is devoted to the study 

 ol heat. The first and second laws ol thermo- 

 dynamics are discussed fully, and the most interesting 

 properties ol solid liquids and gases are dealt with 

 in passing. The graph given on p. 4<>i exhibits 

 the rate of cooling of a teapot as compared with that 

 ol .1 Dewar's vacuum flask, and is interesting as 

 showing thai the rate at which the teapot loses heal 

 is scarcelj affected by radiation, being due almost 

 entirely to convection and, to a small extent, to con- 

 duction. How many teachers, it tn.i\ be wondered, 

 have explained thai a silver teapot loses heat more 

 slowly than a porcelain one, on account ol the high 

 reflecting and consequent low radiating qualities of 

 polished silvi 



(2) Messrs. Hurst and Lattey have written this book 

 for students preparing for the Preliminary examina- 



