Chemistry and Physics. 661 



impact with the ground. This explosion, in our opinion, can be 

 explained very readily in the manner outlined above. It arises 

 from the claquement impressed upon the air by the falling metal, 

 and is just so much the stronger as the velocity and dimensions 

 of the object are greater. — Comptes Rendus, vol. 160, No. 23, 

 June 1915. h. s. u. 



8. Fluorescence and Resonance of Sodium Vapor. — In 

 attempting to extend the brilliant investigations of R. W. Wood 

 on sodium vapor R. J. Strutt has recently obtained the follow- 

 ing important results : 



(a) When sodium vapor is illuminated by the second line of 

 the principal series, at A 3303, it emits the D lines as fluorescent 

 light. 



(b) Illumination by ultra-violet light of other wave-lengths is 

 not accompanied by emission of the D lines. 



(c) If one component only of the ultra-violet doublet (3303) is 

 stimulated, not one alone, but both of the D lines are radiated 

 with approximately equal intensities. " This is an unexpected 

 result, in view of the work of Wood and Dunoyer, who found 

 that stimulation by D 2 light was unable to excite D, light." 



(d) Excitation at A 3303 was found to give rise neither to any 

 observable resonance radiation of the same wave-length, nor to 

 any sensible emission of the lines of the subordinate series. — 

 Proc. Roy. Soc, vol. xci (A), p. 511, August 1915. h. s. it. 



9. Elementary Lessons in Electricity and, Magnetism ; by 

 Silvanus P. Thompson. Seventh edition. Pp. xv, 706, with 377 

 figures. New York, 1915 (The Macmillan Co.). — " For the pur- 

 pose of the present edition the entire work has been completely 

 revised, and in many parts rewritten." A careful comparison of 

 the latest edition with the preceding text, which was reprinted in 

 1914, shows that the first five chapters are practically identical, 

 the only alterations consisting in minor omissions and additions. 

 Lesson XXXV of chapter VI marks the beginning of the rearrange- 

 ment of the subject matter. Not only has the sequence of topics 

 been changed but a great deal of new and important material has 

 been incorporated. To enable those who have accessible a copy 

 of the earlier edition to see at a glance the nature and extent of 

 the revision the titles of the last eleven chapters will now be 

 quoted. They are: "VII Electric Production of Heat; VIII 

 Electric Light ; IX Inductance ; X Dynamos, Alternators, and 

 Transformers; XI Transmission and Distribution of Power ; XII 

 Electric Traction ; XIII Electro-Chemistry ; XIV Telegraphy ; 

 XV Electric Waves; XVI Wireless Telegraphy"; and "XVII 

 Electron Theory of Electricity." The last two chapters are 

 entirely new. 



The seventh edition also possesses the following advantages 

 over the earlier prints. ^ The paper is better, the type larger, and 

 the spacing of the lines* wider. Whenever appropriate the text- 

 figure is accompanied by a legend or brief description of its sig- 

 nificance. The symbols for current, capacity, number in series, 



