596 BELL SYSTEM TECHNICAL JOURNAL 



It has been shown that lead is corroded by contact with moist inert 

 sands in the presence of air, and that the rate of attack is increased by 

 increasing within certain Hmits the particle size of the sand, the mois- 

 ture content of the sand, and the oxygen content of the atmosphere. 



Corrosion is caused by oxygen concentration cells which are set up 

 as a result of the partial or complete exclusion of oxygen at the points 

 of contact of metal and soil. 



Soil particle size influences the rate of corrosion by determining the 

 extent of the electrode areas, and therefore the degree of cathodic 

 polarization, of these oxygen concentration cells. 



Reverberatioji Time in "Dead'' Rooms} Carl F. Eyring. 

 With the advent of radio broadcasting and sound pictures very "dead " 

 rooms have been built, and the significant problem of just how much 

 reverberation should be used in broadcasting and recording presents 

 itself. The direct measurement of reverberation time or its calculation 

 by the aid of a reliable formula, then, is an important aspect of applied 

 acoustics. A reverberation time formula enables one to calculate the 

 reverberation time once the volume, surface area and average absorp- 

 tion coefficient of the surface of the room are known ; or if the reverber- 

 ation time is measured it enables one to calculate the average coefficient 

 of absorption of the surface treatment. A correct reverberation time 

 formula is, therefore, much to be desired. 



Theories of reverberation leading to Sabine's reverberation time 

 equation have been given by W. C. Sabine (1900), Franklin (1903), 

 Jaeger (1911), Buckingham (1925). Recently Schuster and Waetz- 

 mann (1929) have pointed out that Sabine's formula is essentially a 

 "live" room formula and they have shown as we also show that the 

 reverberation time equation varies somewhat with the shape of the 

 room. The present paper presents an analysis based on the assump- 

 tion that image sources may replace the walls of a room in calculating 

 the rate of decay of sound intensity after the sound source is cut off, 

 which gives a form of reverberation time equation more general than 

 Sabine's; it points out the difference between the basic assumptions 

 leading to the two types of formuht; it adds experimental data which 

 support the more general type; and it ends with the conclusion that no 

 one formula without modification is essentially all inclusive. 



The Provision of Radio Facilities for Aircraft ComnmnicationJ E. L. 

 Nelson and F. M. Ryan. This subject is discussed by the authors 

 from the viewpoint of the radio engineer. The periods of fundamental 



■■' Jour. Acou. Soc. Amer., Jan., 1930. 

 * Soc. Auto. Engs., Mar., 1930. 



