proceedings: philosophical society 293 



The 803d meeting was held at the Cosmos Club, March 16, 1918. 

 President Burgess in the chair; 39 persons present. The minutes 

 of the 802d meeting were read in abstract and approved. 



A paper on Thermal expansion of alpha and of beta brass by P. D. 

 ■jNIerica and L. W. Schad was presented by Mr. Merica. This paper 

 was illustrated by lantern slides. Within the past four j-ears an investi- 

 gation has been in progress at the Bureau of Standards of the cracking 

 or fracturing of cast and wrought brass, particularly^ of the type com- 

 position, 60 per cent of copper and 40 per cent of zinc. It has been 

 found that in most failures of such brasses in service the cracking can be 

 ascribed to the presence of initial stresses in conjunction with surface 

 corrosion. These initial stresses may be produced either in the mechan- 

 ical working of the material, such as drawing or rolling or by shrinkage, 

 as in the case of cast metal. As, however, a number of instances of 

 cracking in brass of this type have come to the attention of the authors 

 for which such explanations cannot be applicable, it was their intention 

 to ascertain whether local internal stresses could not be produced in 

 brass of this composition by heat treatment such as it might receive 

 in manufacture. 



Brasses of this type are heterogeneous, consisting of the mechanical 

 mixture of two constituents, called respectively, the alpha and the beta 

 constituents. Measurements of the linear thermal expansion of these 

 two constituents have shown that of the beta constitutent to be con- 

 siderably in excess of that of the alpha. So great is this difference that 

 rough calculations have shown the possibility of the development of 

 average stresses due to the sudden cooling by quenching of the brass 

 containing these constituents equal to approximate!}' 15,000 pounds per 

 square inch. 



Experiments showed that these stresses were probabty responsible 

 for the lowering of the proportional limit of such brasses amounting to 

 as much as .25 per cent. 



The thermal expansion curves illustrate also very well the nature of 

 the thermal transformations in the beta constituent varying about 

 1460°C. 



Discussion: This paper was discussed by Messrs. White, Briggs, 

 and Burgess. 



A paper on The principles of electrical measurements at radio fre- 

 quencies was presented by Mr. J. H. Bellinger. The principles of 

 radio or high-frequency measurements are coextensive with the prin- 

 ciples of radio engineering to an extent not true in other fields. This is 

 typified in the wavemeter, which is a complete radio transmitting and 

 receiving station, albeit in miniature. The principles of ordinary 

 alternating current theory apply with little change to the phenomena at 

 very high frequencies. This was not true a few years ago, when damped 

 waves were universally used in radio work, but the introduction of 

 satisfactory sources of undamped currents has largely eliminated the 

 specialized theory that went with damped waves. 



