482 Scientific Intelligence. 



results are expressed in the form V= Jen — V 0i where V is the 

 velocity measured in volts and n the frequency. Lapenburg's 

 law, that the velocity is proportional to the frequency, has been 

 shown to be incorrect. (3) The values of k and V„ have been 

 found directly for the elements Ca, Mg, Cd, Zn, Pb, Sb, Bi, and 

 As, and the values of V for Se and O a indirectly. (4) The values 

 of k and V for elements of the same valency change regularly 

 with the atomic volume. (5) The product of ~V~ n intoe, the charge 

 of an electron, has been identified with the work required to sep- 

 arate an electron from the molecule." Conclusion (2) is especially 

 worthy of note. — Phil. Trans. Hoy. Soc, London, Vol. 212, A, 

 p. 205. h. s. u. 



9. Magnetism and Electricity • by E. E. Brooks and A. W. 

 Poyser. Pp. viii, 633 ; 413 figures and 414 problems. London, 

 1912 (Longmans, Green & Co.). — This volume has been prepared 

 to replace Poyser's Advanced Magnetism and Electricity, which 

 was originally published in 1892. Nearly the whole of the 

 subject-matter has been rewritten on modern lines, so that, for 

 all practical purposes, the only feature of the old book which 

 remains is the experimental form. "The present work is intended 

 to afford such a range of general reading in the subject as is 

 desirable for the majority of students, before they begin to 

 specialize either in pure science or in the various branches of 

 electrical engineering." An elementary knowledge of algebra, 

 geometry, trigonometry, and mechanics is assumed. Nevertheless, 

 in many instances, the authors supplement the more elementary 

 analysis by short, alternative proofs in which the processes of the 

 differential and integral calculus are used. When the elementary 

 demonstrations would lack rigor or would be very cumbersome, the 

 calculus alone is used. The brevity and elegance of the latter 

 proofs should stimulate the student who is not acquainted with this 

 powerful branch of analysis to increase his mathematical attain- 

 ments. The chapters entitled " Introduction to the Theory of 

 Alternating Currents," " Measurement of Inductance," " Passage 

 of a Discharge through Gases," and "Effect of Inductance and 

 Capacity at Starting and Stopping a Current — Electric Oscilla- 

 tions — Radiation — Wireless Telegraphy and Telephony" are 

 starred to indicate that they may be omitted because of their 

 relatively greater degree of advancement. Of necessity, the 

 proofs in the last of these chapters involve a knowledge of 

 elementary differential equations. The usual symbols K and /x 

 have been retained in the formulae in order to keep the dimensions 

 of the equations correct. 



Throughout the volume, 245 practical exercises are suggested 

 in small print. Many of the qualitative experiments do not 

 require special laboratory apparatus, so that the student can 

 perform them at home with improvised material. The numerical 

 problems and questions are collected in groups at the ends of the 

 chapters, and the answers to the former are given just before the 

 index. Most of the figures are new and all of them are clear-cut 



