﻿Bool' Notices. 193 



and geneially this distinction is ignored. On p. 10 for continual read 

 continuoits. The appeal to " experience" on p. 22, while discussing the 

 purely kinematical motion of a point, is confusing. The value of g is 

 stated on p. 20 for all parts of the earth without limitation. On p. 25 

 the figure is not drawn to the scale described in the text. A much 

 more serious error (p. 90) is the use of the meaningless phrases 

 " the unit of acceleration is one centimetre per second,'' " an accelera- 

 tion of a centimetres per second" several times over. An incline of 5 

 in 100 surely means in 100 along the incline, not along the horizontal, 

 as on p. 153. In the section on Heat (p. 290) "in proportion to" 

 is used in the popular and, in this case, inacclirate sense. On p. 390 

 the figure of the vibrating string is misleading, and at the foot of the 

 page the omission of " inversely"' makes the statement of the number 

 of vibrations give the opposite of the fact. c, at the foot of p. 417, is 

 a misprint for C, and there are misprints of numbers in lines 6 and 7 of 

 p. 418. On p. 436 we read " an electrified body brought near to any 

 other body of different potential will attract it." P. 474 should read 

 " The Grove and Bunsen cells also give ofif." We note on p. 481 "If 

 wires twice as thick are used, the resistance is one half as great," and 

 on p. 503, ' ' Why is dry air a good insulator ? Because it is a 

 non-conductor." Further data are required to solve Questions 2 and 6 

 on p. 369 ; and CD. (p. 431) is not drawn a horizontal through 

 the centre of the needle, as described. The sine of an angle should not 

 be defined as a line on p. 310, while the ordinary meaning of the 

 tangent is assumed on p. 493. 



Passing to more important matters, we think that a strict logical 

 order is too often departed from. Conservation of energy is doubtless 

 the principle by which the branches of Physics should be connected. 

 But surely it should be reached as a generalization after the nieaning 

 and methods of measuring energy have been carefully studied. Instead 

 of this we first have (p. 33) with no better definition than that "energy, 

 or the capacity of doing work, is possessed by matter in virtue of 

 its mass and velocity" (Capitals), a general statement of the conser- 

 vation, transformations, and availability of energy. It is not till p. 95 

 that the student learns how energy depends on velocity, and then only 

 from a definition of the energy as J MV-. Work having been indepen- 

 dently defined as measured by the prodvict of the force into the 

 distance, a numerical example is then taken of the energy acquired by 

 a falling body. Its velocity is calculated (p. 96) from the formula 

 V2 = 2gs. The energy and work done having been deduced from the 

 formulse E — ^MV- and W = FS, it is remarked that these results must 

 necessarily be the same, for the two formulae must, of course, be 

 equivalent. 



Again (on p. 362) in an explanation of polarization, we find, 

 "According to the accepted undtdatory theory of light," though 



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