Barlow, Peter

(1776-1862), mathematician and physicist

by A. M. Clerke, rev. Iwan Rhys Morus

© Oxford University Press 2004 All rights reserved

Barlow, Peter (1776-1862), mathematician and physicist, was born in the parish of St Simon, Norwich, in October 1776. Details of his early life are sparse. He was educated at a local foundation school before starting work in trade; later he became a schoolmaster, and, having by his own exertions attained considerable scientific knowledge, he became a regular correspondent of the Ladies' Diary, then under the management of Dr Charles Hutton, professor of mathematics at the Royal Military Academy, Woolwich.

Barlow first attracted attention as a mathematician. On Hutton's advice he sought, and after a severe competitive examination obtained in 1801, the post of assistant mathematical master, from which he was subsequently advanced to that of professor, in the Royal Military Academy. His first book, An Elementary Investigation of the Theory of Numbers, was published in 1811, followed in 1814 by A New Mathematical and Philosophical Dictionary. In the same year he published his New Mathematical Tables, giving the factors, squares, cubes, square and cube roots, reciprocals, and hyperbolic logarithms of all numbers from 1 to 10,000, together with the first ten powers of numbers under 100, and the fourth and fifth of all from 100 to 1000. His Essay on the Strength of Timber and other Materials (1817, 6th edn, 1867), compiled the results of numerous experiments in Woolwich Dockyard, providing much-needed data for engineering calculations. The experiments on the resistance of iron which formed the basis of the design for the Menai suspension bridge were submitted by Telford to his examination, and were printed as an appendix to the third edition of his Essay (1826). His services to the profession led to his admission, in 1820, as an honorary member of the Institution of Civil Engineers. Barlow was also much occupied with experiments designed to afford practical data for steam locomotion. He sat on railway commissions in 1836, 1839, 1842, and 1845, and two reports addressed by him in 1835 to the directors of the London and Birmingham Company on the best forms of railway equipment were regarded as of the highest authority.

In 1819, with a view to devising a remedy for the large deviations of the compass due to the increasing quantities of iron used in the construction and fittings of ships, Barlow undertook the first experimental investigation ever attempted of the phenomena of induced magnetism. By observing the deflections of a magnetic needle near an iron globe, he established that magnetic intensity depends on the extent of surface rather than of mass. This was shown by Poisson in 1824 to be mathematically deducible from Coulomb's law of magnetic action. In his Essay on Magnetic Attractions (1820), Barlow detailed his experiments, and described a simple method of correcting ships' compasses by fixing a small iron plate in such a position as to compensate for all other local attractions. After successful trial in various latitudes, it was adopted by the Admiralty, although the method proved inadequate in ships built wholly of iron. He received a grant of £500 from the board of longitude as well as presents from the chief naval boards, a gold watch and chain from the Tsar Alexander on the introduction of the device into the Russian navy in 1824, and the gold medal of the Society of Arts in 1821. He was elected a member of the Imperial Academy of Brussels and a corresponding member of the French Académie des Sciences. In 1823 he became a fellow of the Royal Society and he was elected onto its council in 1824. He was also a member of the Astronomical Society and was active in its administration.

Barlow was one of several English experimenters during the 1820s, including Michael Faraday and William Sturgeon, to further develop Hans Christian Oersted's discovery of electromagnetism in 1820. One of his particular contributions was Barlow's wheel, in which a serrated copper disc suspended between the poles of a magnet rotated when an electric current was passed through it. This instrument became a standard demonstration device in the following decades. Some of his results were published in a revised edition of his 1820 Essay (1823), which also included one of the first efforts by an Englishman to produce a comprehensive mathematical theory of magnetism. In 1831 he published the results of an experiment displaying the similarity between the magnetic action of the earth and of a wooden globe coiled round with a current-carrying copper wire. This too became a well-known demonstration device, being on show for example at the Adelaide Gallery of Practical Science in London. This kind of experiment, demonstrating the analogy between natural and laboratory phenomena, was common during the period. Barlow also experimented on the transmission of electricity over long distances, concluding that telegraphy by such a method was impracticable.

Barlow's optical experiments, which began about 1827, arose from efforts to reduce lens aberration in telescopes. Since suitable flint glass was difficult to find, Barlow found a substitute in disulphide of carbon, a perfectly colourless liquid, with about the same refractive, and more than twice the dispersive, power of flint glass. He constructed two telescopes, of respectively 3 and 6 inches aperture, in which the corrections both for colour and curvature were effected by a concavo-convex lens composed of this substance enclosed in glass, of half the diameter of the plate-lens, and fixed at a distance within it of half its focal length. Aided by a grant from the board of longitude, he shortly afterwards advanced to an aperture of 7.8 inches (surpassing that of any refractor then in England), and was willing with some further improvements to attempt one of 2 feet. A committee appointed by the Royal Society in 1831 to report upon the practicability of this daring scheme advised a preliminary trial on a smaller scale, and a 'fluid-lens' telescope of 8 inches aperture and the extremely short focal length of 83Ú4 feet (one of the leading advantages of the new principle) was in 1832 executed by Dollond from Barlow's designs. The success of this trial was not, however, sufficient to warrant the prosecution of the larger design. The 'Barlow lens' later used for increasing the power of any eyepiece was a negative achromatic combination of flint and crown glass, suggested by Barlow, and applied by Dollond in 1833. It was first employed by Dawes in the measurement of minute double stars.

Barlow resigned his post in the Woolwich Academy in 1847, his public services being recognized by the continuance of full pay. He was married but his wife's name is not known. Two sons, Peter William Barlow and William Henry Barlow, were civil engineers. Barlow retained the powers of his mind and the cheerfulness of his disposition until his death, on 1 March 1862, at his home, 13 Maryon Road, Charlton, Kent.

A. M. CLERKE, rev. IWAN RHYS MORUS

Sources  
D. Gooding, 'Experiment and concept-formation in electromagnetic science and technology in England, 1820-1830', History and Technology, 2 (1985), 151-76
PICE, 22 (1862-3), 615-18
Monthly Notices of the Royal Astronomical Society, 23 (1862-3), 127
CGPLA Eng. & Wales (1862)

Archives  
Inst. CE, corresp. and report on London Bridge project |  RS, corresp. with Sir John Herschel
RS, letters to Sir John Lubbock
UCL, letters to T. J. Hussey

Likenesses  
Miss Turner, lithograph, 1835 (after T. Fielding), BM, NPG
S. Cousins, mezzotint (after W. Boxall, exh. RA 1853), BM, NPG [see illus.]

Wealth at death  
under £3000: probate, 26 April 1862, CGPLA Eng. & Wales


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