634 BELL SYSTEM TECHNICAL JOURNAL 



Evaluating Quality in Heat-Treated High-Speed Steel by Means of the 

 Milling Cutter.^ J. B. Mudge and F. E. Cooxey. A test of heat- 

 treated high-speed steel in the form of miUing cutters, the variables 

 having been reduced to a minimum, and the dulling point of the cutting 

 edges of the tools determined by a recording wattmeter connected in 

 the circuit of the motor of the milling machine. A "deadline" test 

 resulted instead of the usual "breakdown" test. 



It was found that: 



Cutters of the same steel hardened by the same method check within 

 limits that are sufficiently close for test purposes. 



No cast cutter has been found to give results comparable to standard 

 high-speed steel refined by suitable working. Cutters hardened by 

 patented or salt bath processes have not given results comparable to 

 standard high-speed steel hardened by the open fire method. 



A Bridge Method for the Measurement of Inter-Electrode Admittance 

 in Vacuum Tubes} E. T. Hoch. A description is given of the 

 Colpitts-Campbell bridge as applied specifically to the measurement 

 of direct admittances in vacuum tubes. Data are given on several 

 tubes. 



On Electrical Fields near Metallic Surfaces} Joseph A. Becker and 

 Donald W. Mueller. When an electron escapes from a metallic 

 surface it passes through fields which tend to pull it back. Applied 

 fields when properly directed partially neutralize the surface fields 

 and hence reduce the work the electron has to do against these fields. 

 That is why i, the thermionic current, increases steadily with Fa, the 

 applied field. Quantitatively (^(logio «')/(/ /^a = (1 1600/2. 3r)X5, where 

 T is the temperature of the surface and 5 is the distance from the 

 surface at which the surface field Fg is equal to Fa. Hence the slope 

 of an experimental log i vs Fa curve at any Fa yields the value of 5 

 corresponding to Fg. For clean or atomically homogeneous surfaces 

 experiment shows that the only force opposing the escaping electron 

 is due to its image field; for composite surfaces other fields, which are 

 ascribed to the adsorbed ions, are superposed on the image field. For 

 70 per cent thoriated tungsten this "adsorption field" is very large 

 close to the surface and in a direction to help electrons escape; it 

 decreases rapidly in strength as s increases until it is zero at about 15 

 atom diameters; here it reverses its direction and then increases in 

 strength till it attains a maximum value of 8000 volts/cm. at 75 atom 



1 Transactions of the American Society for Steel Treating, February 1928, Vol. 13, 

 No. 2, pp. 221-239. 



•^Proceedings of the I. R. E., April 1928, Vol. 16, No. 4, pp. 487-493. 

 'Physical Review, Vol. 31, No. 3, March 1928, pp. 431^40. 



