ABSTRACTS OF TECHNICAL ARTICLES 323 



that important steps have been made toward the analysis of metallic 

 structure. Rapid progress has been made in the last twenty years and 

 today there is available a vast fund of information in regard to the 

 nature of metals in relation to their properties. 



Two of the most important properties of a metal are its hardness and 

 strength. These properties are closely related and in general the 

 magnitude of one indicates the magnitude of the other. The develop- 

 ment of the relationship between the nature of a metal and the hard- 

 ness and strength constitutes one of the most interesting chapters in 

 the science of modern metallurgy. 



Noise Measurement}^ S. K. Wolf and G. T. Stanton. The instru- 

 mental measurement of noise presents difficulties that have in the past 

 generally defeated its successful accomplishment. While noise exists 

 in a physical state and certain of its quantities are susceptible to direct 

 measurement, the magnitude of a noise is evaluated through the inter- 

 pretation of the human ear. The ear is non-linear in its evaluation 

 of the various factors of noise. The degree and nature of the ear's 

 non-linearity to the principal factors is discussed, with respect to the 

 chief interpretative impression, that of loudness. 



Audiometric measurements approached a more proper evaluation of 

 noise, but in addition to dependency upon human judgment, were 

 only approximate, and represented comparisons of physiological effects 

 of noise rather than true noise values. 



An instrument is described that measures intensity expressed in 

 terms of loudness, evaluated for frequency and duration, and which 

 combines portions of a complex wave shape in a suitable manner. The 

 characteristics of the meter and the ear are compared. The readings 

 are in decibels above a zero reference point near the threshold of 

 audibility. The selection and meaning of this scale is explained. 

 Where it is desired to analyze the pitch or frequency of a noise, an 

 analyzer attachment permits either band or single-frequency analysis. 

 Some limitations in its use in making noise measurements are discussed. 



10 Jour. S. M. P. E., December, 1931. 



