Notices respecting New Booh 



583 



and tbe magnetic declination by supporting it in a vertical 

 plane, in such a manner that it could be rotated about a 

 vertical axis, as shown in fig. 3. Its plane could be rotated 



Fi<r. 3. 



until no deflexion of the galvanometer was obtained when 

 mo vin s the slider. This would give the direction of H. It 

 could then be turned at right angles to this position, and the 

 magnitude of H determined in the same manner as has 

 already been described for Z. 



Our inductor was 100 cms. on a side. It could, however, 

 without any serious loss of efficiency be reduced in size to 

 50 cms. on a side or less. 



An advantage of this instrument, -when suitably constructed, 

 would be that it would be universal, as it could be used to 

 determine all the elements of the Earth's field. The method 

 is also very direct, involving only the determination of a 

 current, and the calculation of a self-inductance. 



University of Cincinnati, 

 June 19] 0. 



LXV. Notices respecting New Books. 



Physics. By C. Eiboeg Mank and G. Eansom Twiss. Eevised 

 Edition. Chicago and New York : Scott Foresinan & Companv. 

 Pp. 424. With Illustrations. 

 r PO say that this book will be received with very different feelings 

 -*■ by different readers is only to say that it possesses individuality . 

 It is an attempt to replace the usual elementary course of physics 

 by one in which the problems are more likely to be significant to 

 the average high-school boy or girl just beginning the study of 

 physics. Instead of the "Physics which every Physicist must 

 know" they give what they consider to be the " Physics every 

 child should know.'* The authors are to be commended on the 



