ABSTRACTS OF TECIIXICAL ARTICLES 193 



distinguish in all cases between the results of different physical 

 hypotheses as to the mechanism of flow resistance. A review is 

 given of the physical distinctions which can be determined by such 

 experiments. It is noted that the criterion that the results from 

 different capillary tubes can be expressed in the form Q/R^ = F(PR/2L) 

 serves to distinguish those types of flow in which the resistance is 

 dependent only on the rate and not on the extent of the deformation, 

 except when slip occurs. This last can be distinguished from quasi- 

 laminar flow (in which the resistance depends on the amount of 

 deformation) by tests made with capillaries of common radius but of 

 different lengths. 



The other important physical distinction that can be observed is 

 between those materials which show a yield value and those that do 

 not. For those that do, a new type of equation is obtained, of which 

 the Bingham-Buckingham equation is a special case. In this new 

 general form the relation postulates an initial shear stress which must 

 be exceeded before flow takes place, and a lower constant stress which 

 is effective in opposing flow once the latter has commenced. 



For cases of flow in which no yield value is observed, another new 



form is given which is based on the physical concept, common to 



most theories of such flow, of an effective viscosity varying with the 



stress intensity between upper and lower limits. It is shown that the 



character of this relation is similar to that given by the empirical 



/PR\ " 

 formula Q/R^ = K {-jj^j ■ The use of this equation in expressing and 



interpreting experimental results is discussed. 



Intercontinental Radiotelephone Service from the United States}'' 

 J. J. PiLLiOD. Radiotelephone service between the United States 

 and Europe was established January 7, 1927 with one circuit and 

 with service to limited areas. Facilities and service have been 

 greatly improved and extended and rates have been reduced. Present 

 scope of service is described and reference made to consistent increases 

 in transatlantic telephone messages handled. This increase indicates 

 that this service is being found of increasing value by the public. 



Extent of ship-to-shore radiotelephone service from the United 

 States is outlined. Arrangements for service to Buenos Aires and 

 Rio de Janeiro are described, these differing from arrangements used 

 for service to Europe in that operation to these two cities was planned 

 on a part time basis. Proposed short-wave system for operation with 



" Presented at Pacific Coast Convention of A. I. E. E., Lake Tahoe, Calif., 

 August, 1931. Published in abridged form in Elec. Engg., September, 1931.' 



