. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . s notshown in this view. The operation of theselector is analogous to that of a combina-tion lock. By ingenious governing of therelations of a pawl and the teeth on thecombination wheel, innumerable variantsmay be made, and as a combination lockcan be opened only with its own key, sothe Gill selector can be operated only byimpulses of the prearranged number andsequence. All combination wheels inother selectors on the line fail to reach thecontact position, for the reason that lack-ing the cor
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . s notshown in this view. The operation of theselector is analogous to that of a combina-tion lock. By ingenious governing of therelations of a pawl and the teeth on thecombination wheel, innumerable variantsmay be made, and as a combination lockcan be opened only with its own key, sothe Gill selector can be operated only byimpulses of the prearranged number andsequence. All combination wheels inother selectors on the line fail to reach thecontact position, for the reason that lack-ing the correct sequence of impulsesand intervals, the combination wheel hasbeen returned to its original , though the calling current ener-gizes every selector in the circuit, it ac-tuates to an operative contact only theinstrument at the station desired to becalled. In construction the selector hasbeen reduced to the fewest possible num-ber of parts. Working parts which wouldbe affected adversely by the electric cur-rent are made of non-magnetic selector is mounted on a porcelain. AUTOMATIC CALLING KEY. base, to which its glass cover is hermet-ically sealed. The makers are so confidentthat it will render satisfactory servicethat they will replace at any time instru-ments out of order, if the seal is notbroken. The selector needs no adjust-ment ; it may be installed by the ordinarylineman and needs only to be let alone todo its work properly. As originally designed for telegraph 26 RAILWAY AND LOCOMOTIVE ENGINEERING. January, 1911. service, stations were called through theselector by number with the Morse method may be used where it isdesired to use the line for both telephoneand telegraph service. In fact selectivecalling on a telegraph line presents to adesigner a problem more formidable thanthe corresponding service on a telephoneline. With the telephone, the selecting cur-run is usually of a different characterfrom the voice current and is sent ove
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