.IBSIK.ICIS ()/• Hr.l.l. SYSTluM Tl-.CIINICAI. i'Al'ERS 341 



By the turning of a key the dispatilu-r can (ipon or close any switch 

 or circuit breaker, start or stop any of tlu- machines and receive back 

 ahiiost instantly a visual anil continuous sij^nal of a red or green lamp. 

 The present systems provide in effect a key and two lamps, one red, 

 one green, for each unit sup»r\iM-d mounted in easy access of thi- 

 dis|Mtcher. 



Two main systems known as the distributor supervisory and the 

 selector su|)ervisory have been developed to meet the varying con- 

 ditions of service. 



The distributor system is recommended when there is a large num- 

 ber of units to be su[)ervised in a given station. It consists essen- 

 tially of two niotor-dri\en distributors, one in each station, running 

 in synchronism. Brushes on each distributor pass over correspond- 

 ing segments of two sets of 50 segments at the same instant. Thus 

 by means of only four connecting wires between the stations the con- 

 trol and continuous indication of 50 power units is possible. 



The selector system is recommended when there is only a few 

 switches to be supervised in a single station or in several stations 

 located some distance apart. It consists essentially of hand oper- 

 ated keys to send predetermined codes of impulses to operate se- 

 lectively step by step selectors at the distant stations. After the 

 selector has operated the power unit, an auxiliary contact on this 

 unit operates a motor-driven key to send coded impulses to operate 

 a selector at the dispatcher's station to indicate the condition of the 

 unit by lighting a red or green lamp. Several stations can be super- 

 vised over the same three-line wires. 



The dispatcher, by looking at the lamps on his control boaril, can 

 thus tell at all times the electrical and mechanical conditions at all 

 points in the system and has means to change the operating condi- 

 tions at any substation according to the demand for power. 



Note on Dr. Louis Cohen's Paper on Alternating Current Cable 

 Telegraphy} L. A. M.acColl. This is a criticism of two papers 

 which were published in the Journal of the Franklin Institute by 

 Dr. Louis Cohen. It is shown that Cohen's development of the 

 theorj' of cable telegraphy contains many defects and errors, and in 

 particular that his criticisms of H. W. Malcolm's book, "The Theory 

 of the Submarine Telegraph and Telephone Cable," are without 

 foundation. 



Telephone Circuit Unbalances, Determination of Magnitude and 

 Location.^ L. P. Ferris and R. G. McCurdv. This paper dis- 



' Journal of the Franklin Institute, Vol. 199, p. 99, 1925. 

 • Journal A. I. E. E.. Vol. 43, p. 1 133, 1924. 



