ABSTILiCTS OF TECHNICAL ARTICLES 463 



heated type, are used in simple feedback amplifiers as regulation and control 

 devices to effect the economies inherent in an entirely electrical system by 

 eliminating such mechanical devices as motor-driven condensers, sliding 

 contacts and rotary switches. 



Dynamic Measurejnents on Electromagnetic Devices.* E. L. Norton. A 

 method is presented by which measurements of flux may be made at any 

 desired time during the operate cycle of an electromagnet. Apparatus is 

 described which operates the magnet cyclically at an accurately held rate, 

 and provides a means for measuring flux either by the use of a search coil 

 or by the operating winding of the magnet itself. When using a search coil, 

 it is connected to a direct-current milliammeter at the time in the cycle at 

 which the value of the flux is desired and disconnected at the end of the 

 cycle or just before the magnet is energized for the next pulse. If proper 

 precautions are taken, the steady reading of the instrument is an accurate 

 measure of the difference in the flux in the coil between the time it is con- 

 nected to the meter and the time it is removed, or, since the latter is zero 

 except for residual flux, the reading is a direct measure of flux. 



The same apparatus may be used for the measurement of instantaneous 

 current by the addition of an air core mutual inductance, and its use is 

 extended to the measurement of armature position and velocity by the 

 addition of a photoelectric cell and the proper amplifiers. 



A form of vacuum tube filter is described which effectively filters the 

 pulses from the indicating instrument without affecting the accuracy of the 

 measurements. 



Coaxial Cables and Television Transmission.^ Harold S. Osborne. 

 Communication techniques and facilities useful to the entertainment 

 industry have evolved naturally from the Telephone Companies' main 

 objective — the transmission of speech. The development of carrier sys- 

 tems for long-distance transmission and technical features involved in the 

 latest carrier medium — the coaxial cable — are reviewed. The television 

 transmission capabilities of this medium, both now and what may be 

 expected shortly after the war, are mentioned. The extensive system of 

 such cables planned for the next five years, supplemented by radio relay 

 systems to the extent that these prove themselves as a part of a communica- 

 tions network, will provide an excellent beginning for a nation-wide tele- 

 vision transmission network. Planned primarily to meet telephone 

 requirements, this network of cables will be suitable to meet the transmission 

 needs of the television industry. 



The Performance and Measurement of Mi.xers in Terms of Linear-Xetivork 

 Theory.^ L. C. Peterson and F. B. Llewellyn. This paper discusses 



^ Elec. Engg., Transactions Section, April 1945. 

 'Jour. S.M.P.E., June 1945. 

 « Proc. I.R.E., July 1945. 



