3-48 BELL SYSTEM TECILXICAL JOURNAL 



Measuring Methods for Muiiilaiiiing, the Transmission Efficiency 

 of Telephone Circuits.' V. H. Best. The circuits iiivoKeci in the 

 transmission of speech in a modern telephone plant, particularly 

 those designed for long distance operation, necessarily involve a 

 considerable amount of complexity. The use of telephone repeaters 

 the development of long toll cables, the application of carrier sys- 

 tems and other developments associated with these, while increasing 

 the efficiency and economy of telephone toll circuits have also in- 

 creased their complexity and have required the development of 

 more effective means of insuring that the circuits are maintained 

 at all times in good condition and adjustment. 



Maintenance of the transmission efficiency,' of the telephone plant 

 is conducted by a special force, using methods and apparatus that 

 have been developed for this purpose. This paper gives a brief 

 description of the transmission characteristics of some of the com- 

 mon type of telephone circuits, outlines a general method for measur- 

 ing their transmission efficiency and describes several of the most 

 modern types of transmission measuring sets, together with a brief, 

 mention of the oscillators which supply the power for testing. 



A Primary Standard of Light Follou'ing the Proposal of Waidncr 

 and Burgess.- Herbert E. Ives. The primary standard of light 

 proposed in this paper consists of a black body constructed of plat- 

 inum; the light from which, at its melting point, constitutes the 

 photometric fixed point desired. The platinum black body consists 

 of a cylinder of highly polished platinum with a narrow slit for observ- 

 ing the interior. Studies of the optical properties of reflecting cyl- 

 indrical enclosures show that at certain angles of observation the 

 interior is practically "black." The platinum cylinders are heated 

 electrically and the light from the interior is observed by throwing 

 an image of the slit on to a photometer field. Two .scries of observa- 

 tions were made, one l)y a visual photometric method, the other 

 by a photoelectric cell giving a plu)tographic record by means of a 

 string electrometer. The two methoils of observation ga\e prac- 

 ticalK- identical results, >'ielding a final value for the brightness of 

 the black body at the melting point of platinum of 55.4 candle power 

 per scjuare centimeter. The advantages of this proposed standard 

 over the present imsjitisfactory fiame standards are discussed. 



High Quality Transmission and Reproduction of Speech and Music,^ 

 W. H. Martin and Harvey Fletcher. Radio broadcasting has 



' Joiirn. .\. I. E. K. Vol. XLIII, p. IMh l''i4. 



'Journal Franklin Institute, Vol. 197, p. 147. p. 359, 1924. 



» Journ. .\. I. K. K. Vol. XI. Ill, p. 1M^, 1024. 



