Saturday, July 18, 2009

July 18: Robert Hooke

Robert Hooke
July 18, 1635 – March 3, 1703

Robert Hooke, FRS was an English natural philosopher and polymath who played an important role in the scientific revolution, through both experimental and theoretical work.

Hooke is known principally for his law of elasticity (Hooke's Law). He is also remembered for his work as "the father of microscopy" — it was Hooke who coined the term "cell" to describe the basic unit of life. He also assisted Robert Boyle and built the vacuum pumps used in Boyle's gas law experiments. Hooke was an important architect of his time, and a chief surveyor to the City of London after the Great Fire. He built some of the earliest Gregorian telescopes, observed the rotations of Mars and Jupiter, and, based on his observations of fossils, was an early proponent of biological evolution. He investigated the phenomenon of refraction, deducing the wave theory of light, and was the first to suggest that matter expands when heated and that air is made of small particles separated by relatively large distances. He also deduced from experiments that gravity follows an inverse square law, and that such a relation governs the motions of the planets, an idea which was subsequently developed by Newton. Much of Hooke's work was conducted in his capacity as curator of experiments of the Royal Society, a post he held from 1662.

Hooke was, by all accounts, a remarkably industrious man, and was at one time simultaneously the curator of the Royal Society and a member of its council, Gresham Professor of Geometry and Chief Surveyor to the City of London.

Hooke's reputation suffered during the eighteenth century, and this is popularly attributed to a dispute with Isaac Newton over credit for his work on gravitation; Newton, as President of the Royal Society, did much to obscure Hooke, including, it is said, destroying (or failing to preserve) the only known portrait of the man. Hooke's reputation was revived during the twentieth century through studies of Robert Gunther and Margaret 'Espinasse, and after a long period of relative obscurity he is now recognized as one of the most important scientists of his age.

One of the more-challenging problems tackled by Hooke was the measurement of the distance to a star (other than the Sun). The star chosen was Gamma Draconis and the method to be used was parallax determination. After several months of observing, in 1669, Hooke believed that the desired result had been achieved. It is now known that Hooke's equipment was far too imprecise to allow the measurement to succeed. Gamma Draconis was the same star William Bradley used in 1725 in discovering the aberration of light.

Hooke's activities in astronomy extended beyond the study of stellar distance. His Micrographia contains illustrations of the Pleiades star cluster as well as of lunar craters. He performed experiments to study how such craters might have formed. Hooke also was an early observer of the rings of Saturn, and discovered one of the first double-star systems, Gamma Arietis, in 1664.

On 8 July 1680, Hooke observed the nodal patterns associated with the modes of vibration of glass plates. He ran a bow along the edge of a glass plate covered with flour, and saw the nodal patterns emerge.

The Lunar crater Hooke, a crater on Mars and the asteroid 3514 Hooke (1971 UJ) are named in his honor.

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