Chemistry and Physics. 561 



refractive index of potassium bromide for wave-lengths of the 

 order 0-5 X lO -8 cm. is between 0-999,995 and 1-000,005.— Phil. 

 Mag., xxxi, p. 257, April, 1916. h. s. it. 



S. Long- Range AlphaParticles from Thorium. — In the 

 course of an examination of a strong source of the active deposit 

 of thorium by the scintillation method, Sir Ernest Rutherford 

 observed the presence of a small number of bright scintillations 

 caused by particles which were able to penetrate through a thick- 

 ness of matter corresponding to ll'3 cms of air at 76 cms pressure and 

 15° C. These scintillations were undoubtedly due to alpha-par- 

 ticles possessing a greater velocity than any previously observed ; 

 for, the swiftest alpha-particles hitherto known (namely, those 

 from thorium C) have a range in air of S'6 cms . The number of 

 long-range particles decreased exponentially with the time, falling 

 to half value in 10'G hours — the normal period of decay of the 

 active deposit of thorium. 



The experimental part of the problem was taken up by A. B. 

 Wood and the following conclusions were derived from the 

 observations. The atoms of thorium C can break up in three and 

 probably four distinct ways with the emission of four character- 

 istic groups of alpha-particles. The ranges of these particles in 

 air at 15° C. are, for thorium C, 4-95 cms , for thorium C 2 8-6 cms , 

 for thorium C 3 (new) 10'2 cm3 , and for thorium C 4 (new) ll-3 cms . 

 The respective velocities of the particles were found by calcula- 

 tion to be 1-71, 2-06, 2-18, and 2*26 times 10 9 cms. per sec. The 

 swifter particles appear to be divided into two homogeneous 

 groups amounting together to about 1/10,000 of the total num- 

 ber emitted by thorium C. Approximately two-thirds of the 

 swifter particles have the range ll*3 cm3 . — Phil. Mag., xxxi, p. 379, 

 April, 1916. h. s. u. 



9. The Science of Musical Sounds ; by Dayton Clarence 

 Miller. Pp. viii, 286, with 187 figures. New York, 1916 (The 

 Macmillan Co.). — This admirable book embodies the material pre- 

 sented in a series of eight lectures which were delivered by the 

 author at the Lowell Institute in January and February, 1914. 

 The titles of the lectures were: " I Sound VVaves, Simple Harmonic 

 Motion, Noise and Tone ; II Characteristics of Tones ; III Meth- 

 ods of Recording and Photographing Sound Waves ; IV Analy- 

 sis' and Synthesis of Harmonic Curves ; V Influence of Horn and 

 Diaphragm on Sound Waves, Correcting and Interpreting 

 Sound Analyses ; VI Tone Qualities of Musical Instruments ; 

 VII Physical Characteristics of the Vowels ; VIII Synthetic 

 Vowels and Words, Relations of the Art and Science of Music." 



Since the lectures were addressed to general but cultured audi- 

 ences, a large part of the material was necessarily elementary and 

 well known, and was selected and arranged to develop the prin- 

 cipal line of thought. Consequently there is very little mathe- 

 matical anatysis in the text. Nevertheless, the later chapters 

 involve the most recent progress of the science and give, first 

 hand and in a very dignified, modest manner, a very clear account 

 of the important investigations made in this field by the author. 



