Chemistry and Physics. 465 



discussion of valence. Friedel and Craft's reaction, Grignard's 

 reaction, the reactions of olefins, as well as reactions of oxidation 

 and reduction are extensively discussed. The book is to be 

 recommended to those who are interested in the recent theories 

 in regard to molecular structure. h. l. w. 



6. Experiments with Mechanically -Played Violins. — In con- 

 tinuation of his earlier work (see 48, 74, 1919) C. V. Raman 

 has recently designed, constructed, and experimented with a 

 new form of mechanical violin-player. He says : ' ' The principal 

 feature in the player which is worthy of notice is that the condi- 

 tions obtaining in ordinary musical practice are imitated with 

 all the fidelity possible in mechanical playing, and the results 

 obtained with it may therefore be confidently regarded as 

 applicable under the ordinary conditions of manual playing. 



The most important results recorded in the present paper may 

 be summarized as follows : 



(1) If the speed of the bow is not too low, the bowing 

 pressure necessary within the ordinary musical range of bowing 

 varies inversely as the square of the distance of the bow from 

 the bridge. 



(2) For very small bowing speeds, the bowing pressure 

 necessary tends to a finite minimum value, and the increase of 

 bowing pressure with speed is at first rather slow, but later it 

 becomes more rapid. 



(3) The graph for the bowing pressure for different 

 frequencies shows a series of maxima which approximately 

 coincide in position with the frequencies of resonance of the 

 instrument. 



(4) The mute produces profound alterations in the form of 

 the graph. The bowing pressure necessary is increased in the 

 lower parts of the scale and decreased in the higher parts of the 

 scale. The peaks in the graph shift toward the lower frequencies 

 in consequence of the alteration in the natural frequencies of 

 resonance of the violin produced by the loading, and the change 

 in form of the graph is closely analogous to the change of the 

 intensity of the fundamental tone of the instrument produced 

 by the muting. — Proc. Indian Assoc. Cult. Sci., 6, 19, 1920. 



h. s. u. 



7. Relativity; by Albert Einstein. Translated by Robert 

 W. Lawson. Pp. xiii, 168. New York, 1920 (Henry Holt and 

 Co.). — The present book is intended, as far as possible, to give 

 an exact insight into the theory of relativity to those readers who, 

 from a general scientific and philosophical point of view, are 

 interested in the theory, but who are not conversant with the 

 mathematical apparatus of theoretical physics. The text is 

 divided into three parts which deal respectively with the special 

 theory of relativity, with the general theory of relativity, and 

 with considerations on the universe as a whole. 



The attractiveness and value of the English edition are 



