. Railroad construction. Theory and practice . t, it would have shown the impracti-cability of the combination of No 7 and No. 9 frogs with thisparticular degree of curve, gauge of track, and distance betweentrack centers. If both frogs were made No 9 the total lengthof track between switch points w^ou3d be increased to over 188feet and the point of reversed curve would be nearly at the middlepoint. This shows that the frog numbers should be nearly equal,but also shows that there is some choice *within limitations/ 276. Practical rules for switch-laying. A consideration ofthe previous sections
. Railroad construction. Theory and practice . t, it would have shown the impracti-cability of the combination of No 7 and No. 9 frogs with thisparticular degree of curve, gauge of track, and distance betweentrack centers. If both frogs were made No 9 the total lengthof track between switch points w^ou3d be increased to over 188feet and the point of reversed curve would be nearly at the middlepoint. This shows that the frog numbers should be nearly equal,but also shows that there is some choice *within limitations/ 276. Practical rules for switch-laying. A consideration ofthe previous sections will show that the formulae are compara-tively simple when the lead rails are assumed as circular; thatthey become complicated, even for turnouts from a straightmain traek, v/hen the effect of straight frog and point rails isallowed for, and that they become hopelessly complicated whenallowing for this effect on turnouts from a curved main is also sho\Mi (§ 267) that the length of the lead is practically / VMDN=a: ^ll — i ry II I. Fig. 140. the same whether the main track is straight or is curved withsuch curves as are commonly used, and that the degree of curveof the lead rails from a curved main track may be found with §276. SWITCHES AND CROSSINGS. 293 close approximation by mere addition or subtraction Fromthis it may be assumed that if the length of lead (/.) and theradius of the lead rails (r) are computed from Eq 87 and 90 forvarious frog angles, the same leads may be used for curved maintrack* also, that the degree of curve of the lead rails may befound by addition or subtraction^ as indicated in § 267, and thatthe approximations involved will not be of practical detrimentIn accordance with this plan Table III has been computed fromEq. 87, 88, and 90 The leads there given may be used for allmain tracks, straight or curved. The table gives the degree ofcurve of the lead rails for straight main track; for a turnout tothe inside J add the degree of curve of t
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