. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . (To face page 336.) Plate VIII.—Some Types of Fbogs.(As made by Ramapo Iron Works.) X( § 298. SWITCHES AND CROSSINGS. 337 fillers. For details, study Plate VIII. The operation of aspring-rail frog is evident from the figure. Since a siding isusually operated at slow speed, while the main track may beoperated at fast speed, a spring-rail frog will be so set that thetread is continuous for the main track and broken for thesiding. This also means that the spring-rail wiU only be m
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . (To face page 336.) Plate VIII.—Some Types of Fbogs.(As made by Ramapo Iron Works.) X( § 298. SWITCHES AND CROSSINGS. 337 fillers. For details, study Plate VIII. The operation of aspring-rail frog is evident from the figure. Since a siding isusually operated at slow speed, while the main track may beoperated at fast speed, a spring-rail frog will be so set that thetread is continuous for the main track and broken for thesiding. This also means that the spring-rail wiU only be movedby trains moving at a (presumably) slow speed on to thesiding. For the fast trains on the main Hne such a frog issubstantially a ^ fixed frog and has a tread which is practicallycontinuous. 298. To find the frog number. The frog number (n) equalsthe ratio of the distance of any point on the tongue of the frogfrom the theoretical point of the frog divided by the width ofthe tongue at that point, ==hc-^ab (Fig. 134). This valuemay be directly measured by applying any convenient unit ofmeasure (even a k
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