Peter Barlow

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Peter Barlow was born at Norwich in October 1776. The events during his first years of his life are quite unknown. It is known that he kept a school and gained some scientific knowledge. He became a correspondent to the 'Ladies' Diary', then under the management of a Dr. Hutton, professor of mathematics at Woolwich. By his advice Barlow sought and obtained the post of assistant mathematical master in 1801. He was promoted to the post ofprofessor of mathematics in the Royal Military Academy, Woolwich.

His first book, titled 'An Elementary Investigation of the Theory of Numbers' was published 1811, followed in 1814 by 'A New Mathematical and Philosophical Dictionary'. His best known publication is probably 'New Mathematical Tables' (Barlow's Tables) of the same year, 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 1.000. In 1817 his then most useful book 'Essay on the Strength of Timber and other Materials' gave important information to engineers. These values were gained through numerous experiments in the dockyard of Woolwich.

Barlow invented the technique of fixing a small piece of iron close to a ships compass to compensate for the large deviations due to the increasing quantities of iron in ship construction. After tests in various latitudes it was shown that this did not work on ships build wholly of iron. However, for this invention he received a grant of 500 pounds from the Board of Longitude, from emperor Alexander in Russia a golden watch and chain, and in 1821 the gold medal of the Society of Arts. Between 1823 and 1833 much of his work was on the field of magnetism and electro-magnetism. He even made experiments in signalling by electricity. In a letter he described experiments on the influence of iron on the rates of chronometers.

His optical experiments began about 1827. There were several experiments to correct a single lens for chromatic aberration with concave lenses. These correctors were first placed near the first lens, but some opticians moved the concave lens further down the tube. This arrangement was described 1828 by Rogers in a paper to the Astronomical Society. By this a 3 inch concave flint lens was sufficient to correct a 9 inch crown glass. Smaller lenses near the focus would do the colour correction, but have to have steeper curves which would introduce spherical aberration. The first scope with this arrangement of lenses was made by G. Dollond for Barlow. Making own experiments on achromatic lenses Barlow had some difficulty in getting flint-glass. He replaced the flint by the liquid carbon-disulphide which he contained in glass. This 'liquid lens' was only half the diameter of the front lens and placed in the middle of the telescope tube between the front lens and the eyepiece. The first two telescopes he build with this element had 3 and 6 inches aperture and were corrected for colour and curvature by a concave-convex glass container filled with the liquid. Supported by a grant from the Board of Longitude he build a 7.8 inch refractor, and was willing to try to build a 24 inch telescope.

The Royal Society in 1831 appointed a committee to report on the practicability of this design in this size. The committee requested a 8 inch telescope with 105 inch focal length for further testing. This last telescope of this design was made in 1832 by Dollond. Herschel, Airy and Smyth examined it. They found the light gathering good but rated the chromatic and spherical aberration not enough corrected. The 24 inch was never build.

The now famous 'Barlow Lens' is the result of a collaboration of Barlow with George Dollond. Barlow calculated a concave achromatic lens which Dollond made in 1833 and mounted to a telescope. Dawes employed it first while measuring close double stars. He and Smyth commented favourably on this construction. The invention of this new optical element was presented to the Royal Society by Dollond. (Phil. Trans., 124 pp. 199-207, 1834)

After his optical experiments Barlow was much occupied with experiments for steam locomotion. He sat on railway commissions in 1836, 1839, 1842 and 1845. He resigned his post at Woolwich Academy in 1847, his public services recognized by the continuance of full pay. Peter Barlow died on the 1st of March 1862, aged 86.

Barlow was elected Fellow of the Royal Society in 1823 and received the Copley medal in 1825 for his discoveries in magnetism. He was admitted to the Astronomical Society and sat on the committee for the improvement of the 'Nautical Almanac' in 1829-30. Beside the above mentioned books Barlow contributed several articles for the 'Encyclopaedia Metropolitana' and Rees's 'Encyclopaedia'. The Royal Society's 'Catalogue of Scientific Papers' lists 49 contributions by Barlow to scientific periodicals.

References:

  1. Barlow, P., in: Astronomische Nachrichten, Vol. 1 (1823), p. 31 and 193.

Red Hill Observatory --off site link--

A Chart of Magnetic Curves of Equal Variation by Peter Barlow

William Henry Barlow, Civil Engineer (Peter's son)

This page contributed by Christof A. Plicht


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