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LXVII. Notices respecting New Boohs. 



Maanetism and Electricity; an elementary Text-booh for Students. 

 By Richard Wobmell, D.Sc, M.A. London : Thomas Murby. 

 HIS book is one of a series — the High School Science series. 

 The author informs us that he has aimed at embodying two cha- 

 racteristic features — -first, to make the work progressive in several 

 respects from beginning to end, and, secondly, to introduce the 

 explanation of the latest discoveries and applications of electricity. 

 The latter feature will be commended by every one, but the former 

 will appear to many to be of doubtful utility. Probably it is on 

 that account that the book is thrown into the form of lectures. 

 But are not the functions of a test-book and of lectures different ? 

 A text-book ought to be clear in statement, exact in information, 

 and free from error. We cannot say that these conditions are 

 completely satisfied by Dr. Wormell's book. As regards the first 

 point, there is frequently an ambiguous use of the pronoun it, which 

 is not only inelegant, but causes the reader some pains to find out 

 what is meant. Eor example, " But after the pith-ball has been 

 in contact with the glass rod, it no longer comes towards it, but 

 flies away " (p. 75). " If we rub the glass with silk, then balance it 

 and present the finger to it, it is attracted " (p. 78). " On pre- 

 senting the knuckle to the cover A, after it is lifted off, a spark of 

 positive electricity passes to it, and the plate is discharged "' (p. 88). 

 " If a bar maguet is brought near this loop, it will be made to turn, 

 following the bar magnet, or being repelled from it" (p. 31). The 

 Carrier is described as follows : — " This consists of a metallic ball, 

 a wooden ball covered with tin-foil, a gold-leaf, or some similarly 

 conducting material, attached either to a glass handle or suspended 

 by a silk thread, in order to insulate it." A tyro in electricity is 

 not likely to discern the meaning of this description at first sight. 

 Owing, probably, to the progressive character of the book, many 

 of the statements are not exact enough. Is there any advantage 

 in making a science simpler than it really is ? For example, it is 

 said of the Carrier (loc. cit.) : — " The charge of electricity brought by 

 the carrier is of the same kind as that of the body to be tested, 

 and affects the electroscope exactly in the same way as if the 

 body itself were brought near it." At pp. 52 and 71 magnets 

 and magnetic poles are mixed up in a manner which will give the 

 student some trouble to unravel. "What is meant by " placing two 

 magnets at unit distance apart " ? We have the analogy between 

 potential and level carried a little further than usual, thus : — " The 

 electrical capacity of any body may be measured by the quantity 

 of electricity required to charge it to a given potential : just as the 

 capacity of a cistern for water may be measured by the quantity of 

 water required to fill it to a given level" (p. 111). 



As regards the third point, we have at p. 51 a contradiction 

 within the compass of a paragraph. " If we could increase the 

 weight of the bob without altering the amount of substance com- 

 posing it, we should lessen the number of oscillations per minute : " 



