Barlow, Peter William (DNB01)
BARLOW, PETER WILLIAM (1809–1885), civil engineer, born at Woolwich on 1 Feb. 1809, was the eldest son of Peter Barlow [q. v.] In 1826 he became a pupil of Henry Robinson Palmer, then acting as assistant engineer to Thomas Telford [q. v.] Under Palmer he was engaged on the Liverpool and Birmingham Canal and the new London Docks. In 1827 he was elected an associate member of the Institution of Civil Engineers. In 1834 and 1835 he was employed in surveying the county of Kent for the London and Dover railway, and in 1836 he was appointed resident engineer, under Sir William Cubitt [q. v.], on the central division of the line between Edenbridge and Headcorn. In 1838 and 1839 the sections from Edenbridge to Redhill and from Headcorn to Folkestone were placed in his hands; in 1840 he became resident engineer of the whole line; and subsequently he was appointed engineer-in-chief. In 1842 he designed and executed the Tunbridge Wells branch, a line remarkable from the fact that it was executed, with the consent of the landowners and occupiers, before the act of parliament sanctioning it was obtained. During the next eight years he was engaged on the extension of the Tunbridge Wells branch to Hastings, the North Kent, the Ashford and Hastings, and the Redhill and Reading railways, and from 1850 he was employed in connection with the Newtown and Oswestry, the Londonderry and Enniskillen, and the Londonderry and Coleraine railways. On 20 Nov. 1845 he was elected a fellow of the Royal Society.
In 1858 Barlow investigated, with the assistance of models of large size, the construction of bridges of great span, paying especial attention to the problem of stiffening the roadway of suspension bridges. It had been supposed that to make a suspension bridge as stiff as a girder bridge it was necessary to use lattice girders sufficiently strong to bear the load of themselves, and that such being the case suspension chains were useless. Barlow, however, showed the possibility of stiffening suspension bridges by comparatively light parallel girders extending from pier to pier. Barlow's conclusions have been confirmed by William John Macquorn Rankine [q. v.] (Manual of Applied Mechanics, ed. Millar, 1898, p. 370). While investigating this problem Barlow examined the great railway and road bridge at Niagara, and on his return published 'Observations on the Niagara Railway Suspension Bridge' (London, 1860, 8vo). Shortly afterwards a company was formed for constructing a bridge across the Thames at Lambeth, of which he was appointed engineer. This wire rope suspension bridge, which was opened on 11 Nov. 1862, contained diagonal struts in connection with the vertical ties from which the roadway was suspended. In this way a sufficient degree of stiffness was attained to permit large gas mains to be laid across the bridge without any leakage. Lambeth bridge, 'the cheapest bridge in London,' which cost with its approaches 45,000l., was purchased by the Metropolitan Board of Works (Wheatley and Cunningham, London Past and Present, 1891, ii. 358).
During the construction of the bridge the process of sinking or forcing into the clay the cast-iron cylinders which formed the piers suggested to Barlow the idea that such cylinders could easily be driven horizontally, and could be employed in suitable soils for tunnelling under river beds. In accordance with these theories the Tower subway was constructed in 1869 and 1870 by excavating a tunnel through the clay bed of the Thames by means of a wrought-iron shield, eight feet in diameter, pushed forward by powerful screw-jacks. The subway was completed for 10,000l., and is remarkable for simplicity, celerity, and economy of construction rather than for commercial success. When the tunnel was first opened passengers were conveyed in an omnibus drawn by small steam engines fixed at the Tower and Tooley Street ends. Some difficulties occurring in the working, this plan was abandoned, and it was found necessary to make the passengers walk (ib. iii. 404).
Towards the close of his life Barlow's eyesight was almost destroyed by an attack of cataract. He died at 56 Lansdowne Road, Notting Hill, on 19 May 1885. He contributed a number of treatises to various scientific publications, and wrote several pamphlets.
[Biograph, 1881, v. 597-602; Minutes of Proc. of the Institution of Civil Engineers, 1884-5, lxxxi. 321-3.]