The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . t 1000yards from the entrance the prices per lineal yard were £11, the lower heading; £7, 123. for the upper one ; £30, 10s. forthe unlined tunnel; £45 for the tunnel with a thin lining ofmasonry; and £124, os. with a lining 3 feet thick at the arch,4 feet at the sides, and 2 feet 8 inches at the invert. Lang Tun-nels.—The new Croton aqueduct tunnel from Crotondam to the
The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . t 1000yards from the entrance the prices per lineal yard were £11, the lower heading; £7, 123. for the upper one ; £30, 10s. forthe unlined tunnel; £45 for the tunnel with a thin lining ofmasonry; and £124, os. with a lining 3 feet thick at the arch,4 feet at the sides, and 2 feet 8 inches at the invert. Lang Tun-nels.—The new Croton aqueduct tunnel from Crotondam to the reservoir in New York is worthy of note both for itsgreat length and the rapid progress made with it. The distanceis 33J miles and practically the whole is tunnelled through were sunk about IJ miles apart and headings driven eachway. IngersoU drills were chiefly used, and the rate of advancewith the headings was in 1886 IJ miles per month. The oldCroton aqueduct was 7 feet 8 inches wide by 8 feet 5 inches high ;the new one is 13 feet 7 inches in width and height. Tunnelling in Towns.—Where tunnels have to be carried throughsoft soil and in proximity to valuable buildings special precautions. Flos. 5 and 0.— Noitlicni Railway tunnel. Method of tunnel-ling under the Metropolitan cattle market, London. have to be taken to avoid settlement. The important Metropolitantunnels constructed by Sir John Fowler have already been de-scribed under Railway (vol. xx. p. 239). Another successful ex- I T U N —T U R 625 tmple nf such work is the tunnel driven in 18S6 by Mr Johnson,the Gnat Northeni Companys engineer, under the Metropolitancattle market. WTiere clear of boildin^ the tunnel was executedin 12-feet lengths measured from the hnished brickvork, the ex-caTation extending another 5 feet The Tace of the excavation wascarried out in four sections, the 6rst between the head trees andthe first sill was formed with a rake of 1 in iji, the second andthird with
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