340 BF.l.I. SYSTEM TECHNICAL JOURNAL 



ployed in which a repeater is either built as a conipait unit or is 

 made up of several units which are mounted on I-beams, and sub- 

 sequently interconnected. In the latter case the usual arrangements 

 for sending and receiving from the repeater are omitted, and a sep- 

 arate "monitoring" unit provided for connection to any one of a 

 group of repeaters. 



The metallic system is suitable for providing circuits up to 1,000 

 miles or more in length, the grade of service being better than that 

 usually obtained from ground-return circuits on open-wire lines for 

 such distances. About 55,000 miles of this type of telegraph circuit 

 are in service at present. 



Polarized Telegraph Relays} J. R. Fry and L. A. G.xrdixer. 

 This paper discusses two forms of polarized telegraph relay which 

 have been developed by the Bell System for metallic telegraph cir- 

 cuits and for carrier current telegraph circuits. Both relays are of 

 the same general construction except that one is more sensitive and 

 carries an auxiliary accelerating winding. The more sensiti\'e relay 

 is re(|uired to operate on reversals of line current of one miliiampere, 

 and at the same time retain its adjustment over long periods and 

 faithfully and accurately repeat signals. It is interesting to note 

 that under a\'crage conditions the ratio of power controlled by the 

 contact circuit to that required by the line windings is about 5,000 

 to one. The parts entering into the magnetic circuit of this relay 

 except for a permanent magnet, are made of the new magnetic alloy 

 (permalloy) recently developed in the Bell Telephone Laboratories. 

 Permalloy lends itself to use in this relay because of its high perme- 

 ability and very small residual effects. The design of the rela\- 

 armature and the support for the moving contacts is such that con- 

 tact chatter is practically eliminated. Photo-micrograms showing 

 practically no destructive action are given of the contacts of a relay 

 which was in continuous service for 8^2 months, during which time 

 each contact made and broke its circuit approximately 45, 000, 000 

 times. 



Supervisory Systems for Remote Control.* J. C. Fikld. With tiie 

 great growth in power distributor systems and especially with the 

 advent of the automatic substations with no attendant there has arisen 

 need for a suiierxisory system to indicate to the central load dis- 

 patcher tlie position or operating condition of each important power 

 unit in the outlying stations and also to give him means to operate 

 promptly these power units when desired. 



'Journal A. 1. E. E., Vol. 43, p. 223, 192S. 



' Elfclrical Coiiiiiiuiiicalioiis, Vol. 3, pp.127-133, 1924. 



