546 Notices respecting New Books. 



or at right angles to the radius of curvature ; for as fast as velocity 

 along the radius is generated, so fast does the direction of the radius 

 change ; in the same sort of way that a promise for to-morrow need 

 never be fulfilled, because ' to-morrow never comes ' " (p. 23). To 

 give a puzzled student a hint like this is to " make his face to 

 shine." Once more, in the part on Hydrostatics the question of 

 the pressure on the base and sides of a vessel containing liquid is 

 discussed without algebra or calculation, yet with perfect precision, 

 and each of the student's difficulties is hit off and dissipated by a 

 happy phrase or analogy : then, when by a kind of experimental 

 induction he is led to see how all the cases are converging to a 

 common principle, the last step is taken almost by the student 

 himself — "in symbols, P=sAA. There is nothing more to explain. 

 This simple formula contains it all" (p. 159). How much more 

 truly educative is this method than the other that begins by raising 

 a dust of symbols, and forces a reluctant consent for the bothered 

 and unconvinced reader. 



There is a further excellence in Professor Lodge's method which 

 teachers will value. He every now and then reminds the student 

 that there are large and interesting parts of the subject which are 

 only touched on for the present ; and not content with stating this, 

 he gives him a glimpse of the directions in which these parts lie. 

 He opens up vistas of future interest which encourage the student 

 to persevere, in the hope that if he is faithful he will some day 

 reach wider pastures. Thus at p. 50 enough is hinted to let the 

 student guess " what Eigid Dynamics is about : " he is brought to 

 the point where he must feel that some larger calculus is necessary. 

 The mystery of gravitation is glanced at in pp. 15, 81, and glanced 

 at in the right way, not as hopeless, but as stimulating. The 

 Degradation of Energy is aptly illustrated at p. 84, and its Trans- 

 formation at p. 86 ; a bit of Graphical Statics is worked in at p. 110, 

 with a characteristic note that the bit is " an indication of quite a 

 large art .... which may well occupy the student's attention at a 

 later stage ; w the measures of stability are touched on at p. 130, 

 and meet halfway many perplexities of the inquiring student. 

 Lastly, at p. 164, after finding the vertical fluid pressure on an im- 

 mersed cube, we are told — " If we did not care for simplicity the 

 same might be shown by the symbols for a solid of any irregular 

 shape whatsoever, and a most important mathematical theorem it 

 would be. You may make its acquaintance hereafter in a more 

 general form under the name of Green's theorem.'' 



This, we repeat, is something entirely different from the method 

 of cramming a smattering of all things into a primer : no student 

 can by such allusions as these to advanced matters have his head 

 turned to the vain fancy that he knows all about them ; one and all 

 they come in as baits and lures to more earnest effort now and 

 higher achievement hereafter. 



We need say little here about the good and trustworthy appa- 

 ratus of exercises abundantly provided, or the clearness and patness 

 of the figures, or the terse Saxon of the writing. What we desire 



