CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORATORY, 



HARVARD UNIVERSITY. 



A SIMPLE METHOD OF MEASURING THE INTENSITY 



OF SOUND. 



By George W. Pierce. 



Presented January 8, 1908. Received January 4, 1908. 



I. Introduction. 



In the course of a series of experiments on Detectors for Electro- 

 magnetic waves the writer has found a number of solid substances 

 which, when supplied with contact electrodes and put into electric 

 circuits, serve as rectifiers for small electric oscillations. Some of 

 these substances used in connection with a galvanometer prove to be 

 extremely sensitive and constant in their action and permit the meas- 

 urement of the currents generated by the vibration of the diaphragm 

 of a magneto-telephone under the action of sound waves even when 

 the telephone is at a considerable distance from the source of sound. 



With the use of this device the relative intensity of sound at differ- 

 ent positions in a room may be measured, and many interesting results 

 as to the acoustic properties of an auditorium may be obtained. 



The study of the rectifiers themselves is the subject of a series of 

 papers by the writer, on " Crystal Rectifiers for Electric Currents and 

 Electric Oscillations." Part I of this series of papers appeared in the 

 Physical Review for July, 1907, Vol. XXV, pp. 31-60. The rectifier 

 there investigated is Carborundum. Several other crystal bodies, 

 some of which are in their action much more sensitive than car- 

 borundum, possess similar properties and are being experimentally 

 studied in detail with reference to their electrical characteristics and 

 with reference to their use in electric-wave telegraphy. 



The results of this study will constitute the subject matter of 

 succeeding parts of the Physical Review article. 



II. Molybdenite as a Rectifier for . Electric Oscillations. 



One of the most sensitive of the rectifiers thus far investigated is 

 Molybdenite. The present paper deals with the use of the molyb- 

 denite rectifier in the measurement of sound. 



