150 Notices respecting New Books. 



lines of force will get across the gaps without striking the 

 drum-ends, so that the magnetic field should be produced just 

 as if the drum-ends were not there at all. Thus the metal 

 tube round Rowland's astatic needle system was too far 

 away from the gaps between his sectors on the glass plates to 

 catch the lines of force, so that it could not prevent the field 

 being produced. 



The conclusions arrived at in this paper are : — 



(1) That in Cremieu's attempt to detect the electrostatic 



effect of a varying magnetic field, the effect of the steady 

 magnetic field on the charging currents was left out of 

 account, and that this ]atter effect is equal and opposite 

 to the former. 



(2) That, consequently; Cremieu's negative result constitutes- 

 an indirect proof of the existence of an electrostatic 

 effect of a varying magnetic field, of the amount usually 

 predicted theoretically. 



(3) That in Cremieu's attempt to repeat Rowland's experi- 



ment, his addition of a metallic screen placed close up to 

 the fixed sectors should cause a current to be produced 

 which should almost entirely compensate the desired 

 effect. 



(4) That Cremieu's partial failure without the additional 



screen, is quite possibly due to defective insulation of 



his sectors. 

 In conclusion I wish to say that my best thanks are due to- 

 Prof. J. J. Thomson and to Dr. Larmor for advice and 

 encouragement during the preparation of this paper. 



IX. Notices respecting New Books. 



Magnetic Induction in Iron and other Metals. By J. A. Ewifg, 



M.A., F.H.S., M.Inst.C.E. Third Edition, revised. London: 



'The Electrician' Printing and Publishing Company Limited, 

 1900. 



LITTLE need be said in praise of a book which has on all hands 

 been acknowledged to be the treatise in the English language 

 on the subject of magnetic induction, and the comparatively rapid 

 exhaustion of the first two editions of which is sufficient evidence 

 of the thoroughness with which its distinguished author has 

 accomplished his task. The additions to the original work which 

 appear in the present edition consist mainly of a chapter on 

 "Practical Magnetic Testing," and of references to the more 

 recent investigations, such as those of Dr. Morris on the effects 

 of temperature, and those of Mr. 8. E. Eoget on the "ageing * y 

 of iron by prolonged exposure to various temperatures. The only 

 criticism which we venture to offer is a suggestion that in future 



