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James Gregory (astronomer and mathematician)
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James Gregory (November 1638 – October 1675), was a Scottish mathematician and astronomer. It has been said that "Of the British mathematicians of the seventeenth century, Gregory was only excelled by Newton."
s Gregory was born at Drumoak, Aberdeenshire, and died at Edinburgh. He was successively professor at the University of St Andrews and the University of Edinburgh.
he Optica Promota Gregory described his design for a reflecting telescope, the "Gregorian telescope".
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Encyclopedia
James Gregory (November 1638 – October 1675), was a Scottish mathematician and astronomer. It has been said that "Of the British mathematicians of the seventeenth century, Gregory was only excelled by Newton."
Biography
James Gregory was born at Drumoak, Aberdeenshire, and died at Edinburgh. He was successively professor at the University of St Andrews and the University of Edinburgh.
Published works
Optica Promota
In the Optica Promota Gregory described his design for a reflecting telescope, the "Gregorian telescope". He also described the method for using the transit of Venus to measure the distance of the Earth from the Sun, which was later advocated by Edmund Halley and adopted as the basis of the first effective measurement of the Astronomical Unit.
Vera Circuli et Hyperbolae Quadratura
In 1667, Gregory issued his Vera Circuli et Hyperbolae Quadratura, in which he showed how the areas of the circle and hyperbola could be obtained in the form of infinite convergent series. This work contains a remarkable geometrical proposition to the effect that the ratio of the area of any arbitrary sector of a circle to that of the inscribed or circumscribed regular polygons is not expressible by a finite number of terms. Hence he inferred that the quadrature of the circle was impossible; this was accepted by Montucla, but it is not conclusive, for it is conceivable that some particular sector might be squared, and this particular sector might be the whole circle. Nevertheless Gregory was effectively among the first to speculate about the existence of what are now termed transcendental numbers. In addition the first proof of the fundamental theorem of calculus and the discovery of the Taylor series can both be attributed to him.
The book also contains series expansions of sin(x), cos(x), arcsin(x) and arccos(x). (The earliest enunciations of these expansions were made by Madhava in India in the 14th century). It was reprinted in 1668 with an appendix, Geometriae Pars, in which Gregory explained how the volumes of solids of revolution could be determined.
Gregorian telescope
In his 1663 Optica Promota, James Gregory described his reflecting telescope which has come to be known by his name, the Gregorian telescope. Gregory pointed out that a reflecting telescope with a parabolic mirror would correct spherical aberration as well as the chromatic aberration seen in refracting telescopes. According to his own confession, Gregory had no practical skill and he could find no optician capable of actually constructing one.
The telescope design attracted the attention of several people in the scientific establishment such as Robert Hooke, the Oxford physicist who eventually built the telescope 10 years later, and Sir Robert Moray, polymath and founding member of the Royal Society.
The Gregorian telescope design is rarely used today, as other types of reflecting telescopes are known to be more efficient for standard applications. Gregorian optics are also used in radio telescopes such as Arecibo, which features a "Gregorian dome".
Other work
In 1671, or perhaps earlier, he rediscovered the theorem that 14th century Indian mathematician Madhava of Sangamagrama had originally discovered, the arctangent series
for ? between −p/4 and p/4.
This formula was used by Madhava to calculate digits of π and later used in Europe for the same purpose, although more efficient formulas were later discovered.
James Gregory discovered the diffraction grating by passing sunlight through a bird feather and observing the diffraction pattern produced. In particular he observed the splitting of sunlight into its component colours - this occurred a year after Newton had done the same with a prism and the phenomenon was still highly controversial.
Gregory, an enthusiastic supporter of Newton, later had much friendly correspondence with him and incorporated his ideas into his own teaching, ideas which at that time were controversial and considered quite revolutionary.
The crater Gregory on the Moon is named after him. He was the uncle of mathematician David Gregory.
See also
External links
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