Chemistry and Physics. 393 



was first used and in which the great utility and preeminent 

 importance of this function was first made plain. Few, if any, 

 improvements in the presentation of the general theory have 

 been made in the seventy-five years since its publication, and it 

 has. all the advantage of being the original work of a great 

 genius and of showing in a measure the processes by which he 

 reached his results. That such a work should have been pro- 

 duced by a young man without any mathematical training except 

 what he could gain for himself is one of the most interesting 

 chapters in the natural history of genius. Some of the other 

 papers are of less direct interest at the present day ; that on the 

 propagation of light in crystallized media, however, is still the 

 foundation of the theory of the elasticity of seolotropic solids 

 and cannot be neglected by the student who desires a compre- 

 hensive knowledge of the history of this important subject. 



H. A. B. 



14. Electric and Magnetic Circuits; by Ellis H. C rapper. 

 xi -1-379 pp. New York, 1903 (Longmans, Green and Co.). — The 

 plan of this elementary text-book for students of electrical engi- 

 neering is not unlike that of the school arithmetics in which a 

 large number of numerical examples are propounded for solution 

 by the student, each collection of problems bring prefaced by a 

 brief statement of the "rules" necessary for solving them, and by 

 two or three worked-out examples. The explanatory portions 

 leave much to be desired especially in the more elementary 

 sections. The definitions are often inaccurate and sometimes 

 quite meaningless, as on p. 3 where the ampere is defined as " the 

 time rate of change of the coulomb 'per second." The expla- 

 nations often give entirely wrong ideas of the relations between 

 electrical quantities and of the laws which express them, as in the 

 discussion of E.M.F. and P.D. on pp. 34 and 35 and the curious 

 statement on p. 39 that the constant ratio of the E.M.F. to the 

 current "was discovered hj Ohm to be equal in all cases to the 

 total resistance of the circuit". Most of the formulae used for 

 solving the problems are introduced as depending directly upon 

 experiment with no indication that they might easily be deduced 

 from preceding ones ; it is hard to believe that there is any very 

 large number of students of electricity so deficient in logical 

 memory as to find this method easier and more "practical" than 

 an orderly and logical presentation. A still more serious defect, 

 in a book primarily intended to teach engineers to calculate, is 

 that no attention is paid to the limits of accuracy in data and 

 results. In the illustrative examples, currents and resistances are 

 calculated to six or seven significant figures, the cost of incan- 

 descent lights per candle-hour is determined to the ten-millionth 

 of a penny, and in one case (p. 306) the torque exerted by a 

 motor is calculated to eleven figures from data given to four figures. 

 Such calculations cannot be regarded as good models for imitation 

 by future engineers. h. a. b. 



