430 BELL SYSTEM TECHNICAL JOURNAL 



quently, copious references to the experimental results of other 

 workers have been included. The material is grouped under four 

 headings: (1) Speech, (2) Music and Noise, (3) Hearing, and (4) 

 Perception of Speech and Hearing. 



The first part is concerned with the mechanism of speaking, the 

 classification of the fundamental English speech sounds, and with the 

 wave forms of such sounds. It includes a description of various 

 types of apparatus which can be used for making permanent records 

 of speech waves and gives a large number of accurate wave pictures 

 of the speech sounds together with the power contained in such waves. 



In the second part similar data are given for musical sounds and 

 noise. 



The third part begins with a discussion of a theory of hearing which 

 is proposed to explain the experimental facts of audition. This is 

 followed by a discussion of the known facts of audition such as the 

 limits of audition, the minimum perceptible differences in sound, 

 masking effects, binaural effects, methods of testing the acuity of 

 hearing, etc. Along with this discussion is given a description of the 

 apparatus and experimental methods used for determining these facts. 



The fourth part is concerned with those phases of the subject that 

 involve personal judgment, that is, the psychological element. A 

 scale for measuring the loudness and the pitch of complex sounds is 

 defined. Experimental data are given which show how these two 

 subjective quantities depend upon external physical quantities. 

 Methods of measuring the recognition of speech sounds are described 

 and experimental results using such methods are given to show the 

 effect of various types of distortion upon the ability of persons to 

 recognize such distorted sounds. 



Elementary Differential Equations.^ Thornton C. Fry. In this 

 book Dr. Fry has covered the field of differential equations as usually 

 offered in elementary courses in universities and technical schools. 

 The mathematical ideas are first presented as mathematical entities 

 in themselves and not as the symbolic formulation of physical concepts. 

 With this accomplished, these ideas are broadened and illustrated by 

 live scientific examples and problems, which are drawn from a wide 

 variety of fields. The inclusion of such technical material does not 

 presuppose a wider knowledge of technical subjects than the reader 

 can reasonably be expected to possess, nor does it interfere with the 

 clarity of the mathematical presentation. 



* D. Van Nostrand Company, Inc., New York, 1929. 



