630 BELL SYSTEM TECHNICAL JOURNAL 



Some Improvements in Toll Circuit Design and Transmission} Glen 

 Ireland. Progress did not crash, along with the stock market, in 

 1929. Subsequent years have seen astonishing advances in many 

 important businesses of the country as regards scientific develop- 

 ments, improved methods and better service. This is particularly 

 true in the allied fields of transportation and communication where 

 the service has been made more and more convenient, comfortable and 

 accessible. Mr. Ireland's work lies in the field of communication and 

 more specifically has to do with toll circuit design and transmission. 

 In this paper he tells something of the progress in this field; first with 

 respect to some new toll circuit instrumentalities that may be of direct 

 interest in the work of the railroads, and secondly about some im- 

 portant and fundamental improvements, which are of general interest 

 as indicating the trends in the art. 



The general practices followed in connection with the design and 

 installation of toll cables in the Bell System were described before the 

 Telegraph and Telephone Section of the Association of American Rail- 

 roads several years ago. There have been several specific changes in 

 practices and some improved instrumentalities made available in this 

 field which it is believed will be of interest to the railroads. 



Calculated and Experimental Photoelectric Emission from Thin Films 

 of Potassium.^ Herbert E. Ives and H. B. Briggs. Several years 

 ago one of the writers proposed a theory of the photoelectric emission 

 from thin films of alkali metals on supports of other metals, not 

 photoelectrically active in the regions of the spectrum under observa- 

 tion. According to this theory the photoelectric emission is pro- 

 portional to the rate of energy absorption by the thin film of alkali 

 metal. The magnitude of the photoelectric current depends on the 

 energy density immediately above the supporting metal, which is 

 established from a knowledge of the optical constants of that metal, 

 and upon the specific absorption of the alkali metal film. For its 

 verification, the theory demands a knowledge of the optical constants 

 of both supporting and alkali metals throughout the whole region 

 of the spectrum where observations can be made. While optical 

 constants have been determined for platinum, which is the metal most 

 commonly used for a support for these thin films, no optical constants 

 for the alkali metals have been available except in the visible region. 

 In this region, a very satisfactory confirmation of the theory was 

 obtained, particularly in respect to the variation of emission with the 

 angle of incidence for the two principal planes of polarization (vectorial 

 effect). One of the most characteristic phenomena of photoelectric 



'" Proc. Assoc. Amer. Railroads — Telegraph and Telephone Section, June, 1935. 

 ^ Jour. Opt. Soc. Amer., June, 1936. 



