. Railway track and track work . , however, the corrugations are on the face of thelens, as at C, Fig. 70. The ordinary size of lens is 5 or 5| ins. for semaphoresand main-line f^witchstands. A diameter of S ins. is sometimes employed forlamps at bridges, tvmnels and crossings. The lamps for yard switches anddwarf signals may have 4-in. or 44-in. lenses. Backlights may be 2 ins. diame-ter. With good lamps, ordinary lenses, and no reflectors, the lights will be 138 TRACK. visil)le for from 1 to 3 miles in clear weather. They will be stronger and sharperwith reflectors. Yellow lights cannot be s
. Railway track and track work . , however, the corrugations are on the face of thelens, as at C, Fig. 70. The ordinary size of lens is 5 or 5| ins. for semaphoresand main-line f^witchstands. A diameter of S ins. is sometimes employed forlamps at bridges, tvmnels and crossings. The lamps for yard switches anddwarf signals may have 4-in. or 44-in. lenses. Backlights may be 2 ins. diame-ter. With good lamps, ordinary lenses, and no reflectors, the lights will be 138 TRACK. visil)le for from 1 to 3 miles in clear weather. They will be stronger and sharperwith reflectors. Yellow lights cannot be seen as far as red or green. Theprism glass reflector is being favorably considered for signal lamps; it increasesthe intensity of the light, and is free from the deterioration in reflecting powerafter long service, such as is experienced with metal reflectors. (See alsoSignals.) To insure the lamp being in proper position on the switchstand, the socketor fork should be so shaped tiiat the lamp can be put on only in one B. C Fig. 70.—Switch Lamps. If the socket on the lam]) fits on tlie top of the vertical shaft of the switchstan;!,the top should be rectangular instead of square, or one corner of the socketmay be filled up to fit a chamfered corner of the rod. The lamps slioiil 1 bekept clean, in good repair and properly trimmed, the lenses especialh beingwiped free from grease and dirt. The wick should rarely be cut with shears,but the charred crust may be scraped off with a match stick. The light shouldbe turned down as soon as lighted, and in a few minutes gradually turned upto give the proper size of flame, being watched for a few moments to -see that SWITCHES AND FROGS. l;:i9 it burns steadily and does not flare or smoke. When the light is extinguishedthe wick should be turned down to prevent waste of oil. Long-liurning lampswith large fovmts are being extensively adopted, but should not be used formore than four to six weeks, as the wick will become clogged wi
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