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��Showing a train seeking to enter the block be- yond the "home" sig- nal. Engineer knows by the fact that "dis- tant" signal is up that the home signal is also up, even though he may not be able to see the latter, due to smoke, fog, or an obstruction
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��Engineer sees that the distant signal is down and knows that ' the home signal is also clear. He therefore goes ahead at the regular or full speed. A "home" sig- nal is so called because it is nearest "home '; or in the block the train .seeks to enter
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��Something is wrong. The distant signal is down without the home signal being correspond- ingly clear. This shows how a block system sometimes fails. Auto- matic train control is designed to stop the engineer safely at home signal in such a case
��Popular Science MontUy
these much-needed contrivances, the Govern- ment has for several years maintained a corps of trained investigators who will go to almost any part of the country and test out free of charge any invention of the kind that gives promise of being worth while. Moreover they will make an authoritative report on its merits, if it proves worthy of attention. This corps has given much practical aid to inventors, and done much through suggestions to standardize and improve the inventions being put out. At present we are on the road to a practical train-stop.
To illustrate the general train-stop situation specifically, we will show how one of the best train-stops operates. Let us take the type recently perfected by Jean F. Webb, Jr., of New York city. As the pictures on page 438 show, the apparatus is affixed to the buffer-beam at the front of the engine. Other inventors attach their stop to the tender, or even beneath the cab. Some have attempted to locate most of the apparatus along the roadway and have it struck by a projection on the engine as the latter goes by. This, however, seems to be a wrong plan in most cases, since the great force of such a broad- side impact may result in breaking the appa- ratus to pieces.
The ramp principle Mr. Webb uses is begin- ning to be recognized as the most satisfactory out of the number of alternatives. As the engine and train approach a block signal, the shoe part of the apparatus runs up a short piece of inclined rail, or T-iron, say thirty feet long. This piece of inclined rail is called a "ramp.' ' As the shoe rides up over the ramp it opens the air valve on
��437
���The complication of signals an engineer encounters in an ordinary railroad yard which covers an area about two miles long and about one and «ne- quarter mile wide. All tracks are single tracks; the parallel nes represent ra'. r
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��Showing more compli- cated signals than the preceding. Engineer has whistled for side- track. Towerman ac- cordingly gave it to him, at the same time lowering the lower of the two arms at the home signal — which in- dicates that everything is ready for the train to proceed to side track
���Still more complicated signals, showing what mixed up propositions an engineer encounters. He must read the sig- nals almost instantly and correctly or cause trouble for himself and train. Here signals mean main line is closed but sidetrack is open
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