John Henry Pratt

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Drawing by JH Pratt (1839)

John Henry Pratt (born June 4, 1809 in London , † December 28, 1871 in Ghazipur , India ) was an English cleric and mathematician . He devised a theory of the balance of the earth's crust , which became one of the cornerstones of the theory of isostasis , and correctly recognized that the earth is flattened at the poles . His determination of this flattening as the difference between the axes through the pole and the equator corresponded to 26.9 miles (43.3 km), almost the value known today.

Life

Pratt was born the son of Elizabeth Jowett and Josiah Pratt, a vicar of the Church of England . He attended Oakham School in Rutland , before settling in 1829 at Gonville and Caius College of the University of Cambridge enrolled, which he in 1833 with a Bachelor of Arts graduated. In 1836 he received his Masters from Christ's and Sidney Sussex College . Under the influence of his father, he embarked on a spiritual career and in 1838 became a chaplain with the East India Company . Six years later he moved to Daniel Wilson, the then Bishop of Calcutta , and another six years later he became Archdeacon of Calcutta in 1850 . In 1871 he died of cholera while visiting Ghazipur in the state of Uttar Pradesh .

plant

His first work was The Mathematical Principles of Mechanical Philosophy and their application to Elementary Mechanics and Architecture, but chiefly to The Theory of Universal Gravitation , a work of more than 600 pages, the first edition of which was published in 1836 and initially under the short title Pratt's Mechanical Philosophy became known. The second edition appeared in 1842 and, after a thorough revision, the third in 1860, this time under the title On attractions, Laplace's functions and the figure of the Earth . In addition to his scientific work, Pratt published some theological works, his book Scripture and science not at variance , published in 1856, attempted to reconcile science and belief and was reprinted several times.

He developed his theory of the balance of the earth's crust on the basis of a survey of the land that George Everest had carried out. When the results of the trigonometric measurement of the longest distance between the northernmost and southernmost points of India were compared with that from astronomical , there was a small difference between these numbers. Everest explained this difference with measurement errors , but Pratt sought the cause in the fact that the mass of the Himalaya distracted the lead plumb bobs used in the measurement . In pursuing this theory, he discovered that the deflection of the plumb bob couldn't have been as great as he had calculated from the density and volume of the mountains: the difference between trigonometric and astronomical longitude should have been greater than determined. As an explanation, he assumed that the density of the earth's crust in the Himalayas was lower than in the plain. His theory appeared in the same year as the second theory of isostasy developed by George Biddell Airy .

In 1866 Pratt was made a Fellow of the Royal Society .

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personal data
SURNAME Pratt, John Henry
BRIEF DESCRIPTION British mathematician
DATE OF BIRTH June 4, 1809
PLACE OF BIRTH London
DATE OF DEATH December 28, 1871
Place of death Ghazipur , India