RAILWAY.

189

METHOD OF USING THE TABLES.

For the Trunk or Central Part in a Cutting or Embankment. —Add together theheight in feet of the two ends; then look for this No. in the first column of Table I.,and on the same line, under the proper length in chains, will be found the contentin cubic yards. Should the length exceed 9 chains, the content must be taken outin two operations. The content thus obtained is for 1 foot only in width; the totalquantity must be multiplied by the true width in feet.

For the Slopes on the Side of a Cutting or Embankment.—If the embankment hasa height at only one end, the content in cubic yards is given at once in Table II.;the height in feet being contained in the outside vertical columns.

If the embankment has a height at each end, multiply the two heights together;look for this No. in the outside column of Table I., and take out the No. on the sameline under the proper length (a). Then subtract the lesser height from the greater;look for this No. in the first column of Table II., and take out the No. on the sameline under the proper length (b). These two ( a and b) added together will give thecontent in cubic yards, for any length not exceeding 9 chains: when greater thanthat, it must be taken out in two operations. The content thus obtained is forone side only, calculated upon a slope of 1 to 1: the total quantity must be doubled;and for any other slope, must he multiplied by the ratio of the base to the height.

If the lengths are in feet instead of chains, these Tables may equally well be used,by taking the figures in the top line as feet, and dividing the total result by 66. (Seeexample, p. 188.)

The main art of directing earthworks consists in so proportioning the men to eachtask, and disposing the materiel or plant, that none shall for a moment stand idle, andthat a free passage shall be continually kept open. These proportions depend upon localcircumstances, and can scarcely even approximately he made the subject of calculation,but, together with the disposition of the men, depend on the judgment of the Engineer.

Cuttings. —In commencing an excavation, a face at right angles to the directionof cutting should be obtained, and a gullet, of about 15 feet wide, formed as soon aspossible. The accompanying sketch shews a mode of cutting niches with the pick-

Fig. 5.

1, *r

axe, and a very little labour enables the excavator to separate the masses between..Into the gullet, when formed, a train of waggons to receive the earth is sent. Asthe height of the hill increases, side tracks on a higher level are laid down, and theinclines which connect them with the first line serve to enable the loaded carriagesto draw up the empty ones. Plate XXVIII. shews the above-described method.