.IFSTRACTS OF PF.l.l. SYSTF.M TECIINICAL PAPERS 345 



pciulently of one another. Static in r.iclio tek-phony anil rcrl.iiii 

 types of crosstalk probably satisf\- these conditions. 



The Transmission i'nil." R. \'. L. H.vrti.ky. The Bell System 

 has recently adopted a new transmission unit, abbreviated TU, for 

 ex[>ressing those quantities which heretofore have been expressed in 

 miles of standard cable, or in Fairofie in terms of the fil unit. It *is 

 shown that units of this t>pe measure the logarithm of a ratio, and 

 that the present art reijuires that this ratio be tiiat of two amoimts 

 of [lower. Any of the proposed units may be so defined. Their 

 essential difference is in the ratio chosen to correspond to one unit. 

 The ratio chosen for the TU, 10 ' , makes it nearly the same in size 

 as the 800-cycIe mile, which has advantages. It also facilitates the 

 use of common logarithms in preference to natural logarithms for 

 which the ratio e of the /3/ unit is adapted. A distortionless refer- 

 ence system calibrated in 7"C/ is discussed, and conversion tables for 

 the various units are given. 



The Thermionic Work Function of Oxide Coated Platinum}^ C. 

 D.wissoN anf! L. H. Germer. Measurements of the thermionic 

 work function of pure platinum coated with oxides of barium and 

 strontium have been made simultaneously by two methods for the 

 same segment of a uniformly heated filament. The theory of the 

 measurements and the experimental arrangements are the same as 

 used in an earlier e.xperiment on the thermionic work function of 

 pure tungsten." Filament temperatures accurate to ±5°, were found 

 from the resistance of the filament at 0° C. in conjunction with the 

 temperature coefficients of resistance, (l) In the Calorimclric method 

 the equivalent voltage of the work function was computed from the 

 sudden voltage change resulting from switching off the space current, 

 due to the cooling effect of the emission. The determination was 

 much more difficult that in the case of the tungsten filament, and 

 measurements were made at the signle temperature, 1064° K. At 

 this temperature the work function <i> was found to be equal to 

 l.70±.03 volts. (2) In the temperature \ariation method ii was 

 ftiund that, after the temperature had been changed suddenh from 

 one value to another, the emission changed approximately exponen- 

 tialh' from an initial value to a final steady value. The half value 

 pericKl of this change varied from a few seconds at high temperature 

 to over a quarter of an hour at low temperature. Interpreting this 



'• Klectrical Communications, July, 1924. London Klectrician, January 16 and 

 U. 1025. 



" Physical Review, Vol. 24, p. 666, 1924. 



" Uavisson and Germer, Phys. Rev., 20, 300 (1922). 



