GRAY 



force was known as the force of 

 gravity. A similar attraction ac- 

 counted for the motion of the moon 

 around the earth, this force being 

 smaller than the attraction of the 

 sun in proportion to the much 

 smaller mass of the earth. 



The next step in the develop- 

 ment of the theory was to extend 

 the operation of the attractive force 

 of gravity to the small particles of 

 matter which ultimately make up 

 the masses of the great heavenly 

 bodies. Newton showed, for ex- 

 ample, how the small attractions 

 of the earth's particles would com- 

 bine to form the joint attraction 

 to the centre of the earth, and was 

 thus led to his formula of gravita- 

 tion : " Every material particle in 

 the universe attracts every other 

 particle with a force whose direc- 

 tion is that of the line joining the 

 two, and whose magnitude varies 

 directly as the product of their 

 masses, and inversely as the square 

 of their distance apart." Newton 

 made no attempt to account for 

 this attractive force, which, it 

 should be noticed, was independent 

 of the kind of matter, and acted at 

 a distance without any obvious 

 medium of transmission. 



Theory of Relativity 



Such was the theory of gravita- 

 tion as it left the hands of Newton, 

 with difficulties which no one 

 perceived more clearly than its 

 originator, but still a marvellously 

 successful explanation of ob- 

 served facts so far as it went. In 

 spite of the advances made in 

 physical science during the inter- 

 vening two centuries, no more was 

 learnt about the nature of gravi- 

 tation until within the last few 

 years. Knowledge was gradually 

 accumulated as to the nature of 

 light and the operation of elec- 

 trical forces, and great generali- 

 sations like the " conservation of 

 energy " were introduced and con- 

 sistently verified, but gravitation 

 long remained obstinately apart, 

 an obscure enigma which still pre- 

 sented the anomaly of an incom- 

 prehensible " action at a distance." 

 Certain difficulties in the theories 

 of light and electricity led to the 

 introduction, in the early years of 

 the twentieth century, of the so- 

 called theory of relativity, which 

 has had a revolutionary effect on 

 the fundamental ideas of mechanics 

 and physics, and in the hands of 

 Einstein has thrown a new light 

 on the problem of gravitation. 



Einstein obtained a new law of 

 gravitation, derived not from ob- 

 servation, but from pure reasoning, 

 which differs but slightly from 

 Newton's law in its application to 

 the cases within our knowledge. 

 There were three deductions from 



Einstein's theory of gravitation in 

 which its differences from New- 

 ton's law were open to experi- 

 mental verification, and in two of 

 the three cases the result has gone 

 in favour of the new theory. 



According to Einstein the ellipses 

 in which the planets revolve about 

 the sun should themselves be in 

 course of gradual rotation ; such 

 an effect had long been known in 

 the case of the planet Mercury, 

 although the amount of the rota- 

 tion was extremely small, amount- 

 ing only to 43 seconds of arc in the 

 last century. Einstein was suc- 

 cessful in showing that this result 

 would follow from his theory, cor- 

 rect to a second, and also that in 

 the cases of the other planets the 

 effect would be too small to be 

 measurable. 



The second deduction from the 

 theory was that light rays, passing 

 near the sun, would be deflected 

 from their course by a calculable 

 amount ; this prediction was veri- 

 fied in the most striking way by 

 the British solar eclipse expedition 

 of 1919. 



The third deduction, a tiny dis- 

 placement of the lines in the sun's 

 spectrum, is still (November, 1920) 

 a matter of dispute. 



Although it is as yet too soon to 

 pronounce definitely that Ein- 

 stein's theory contains the whole 

 truth about gravitation, its success 

 in explaining the observations of 

 astronomers entitles us to credit 

 its originator with a step forward 

 comparable to that of Newton, 

 while the derivation of the law of 

 motion of the universe from 

 general reasoning may justly be 

 considered the most astonishing 

 example of the power of pure 

 thought in the history of science. 



Gray, ASA (181 0-88 ). American 

 botanist, Born at Paris, New York 

 State, Nov. 18, 1810, he entered 

 the medical 

 school at Fair- 

 field a t the 

 age of 16. He 

 qualified as a 

 physician, but 

 never prac- 

 tised. Before 

 he was of age 

 he had entered 

 into corre- 

 spondence 

 with leading botanists, including 

 John Torrey, the state botanist, 

 whose assistant and colleague he 

 ultimately became. 



In 1838 the new university of 

 Michigan offered him the chair of 

 botany, which he accepted on con- 

 dition that he might first spend a 

 year of study in Europe. But 

 an engagement with Torrey kept 

 him in New York, and from 1842 



Asa Gray, 

 American botanist 



until his death he was professor 

 of natural history at Harvard. 

 He died at Cambridge, Massachu- 

 setts, Jan. 30, 1888. 



Gray, DAVID (1838-61). Scot- 

 tish poet. Born near Kirkintilloch, 

 Dumbartonshire, Jan. 29, 1838, 

 the son of a hand-loom weaver, he 

 was educated at Glasgow Univer- 

 sity. In 1860 he came to London 

 with Robert Buchanan (q.v.) to 

 begin a literary career. He died 

 Dec. 3, 1861, of consumption, de- 

 veloped from a cold caught from 

 spending his first London night in 

 Hyde Park. His best work is his 

 sonnet sequence, In the Shadows. 

 See David Gray and other Essays, 

 R. Buchanan, 1868. 



Gray, ELISHA (1835-1901). 

 American inventor. Born at 

 Barnesville, Ohio, Aug. 2, 1835, in 

 1867 he brought out a patent for an 

 improved telegraph apparatus, and 

 nine years later filed specifications 

 for the telephone, which he claimed 

 as his own invention. The U.S. 

 supreme court, however, awarded 

 the patent to A. G. Bell. "Gray 

 invented many improvements in 

 telegraph and telephone appli- 

 ances, which he manufactured at 

 Chicago and Cleveland. He died 

 at Newtonville, Massachusetts, 

 Jan. 21, 1901. 



Gray, GEOKCE (b. 1892). Aus- 

 tralian billiard player. Son of 

 Harry Gray, the professionalcham- 

 p i o n billiard 

 player of 

 Queensland, 

 when only 17 

 years of age 

 he created a 

 sensation in 

 the billiard 

 world by his 

 wonderful haz- 

 ard play, mak- 

 ing 831 off the 

 red ball in a 

 break of 836. 

 Jio came to 

 England in 

 1910. While 



George Gray, Aus- 

 tralian billiaid player 



playing n gainst 

 Harverson in London on March 17- 

 18, 1911, he compiled, using crystal- 

 late balls, an unfinished break of 

 2,196 (1,944 being off the red). 



Gray, JOHN EDWAKD (1800-75). 

 British naturalist. Born at Wal- 

 sall, Feb. 12, 1800, he entered the 

 British Museum as an assistant in 

 1824, and in 1840 was appointed 

 keeper of the zoological collections. 

 He wrote various works on natural 

 history, ranging from whales down 

 to seaweeds, and was noted for his 

 study of the British non-marine 

 mollusca. He died March 7, 1875. 



Gray, THOMAS (1716-71). Eng- 

 lish poet. Born in London, Dec. 

 26, 1716, the fifth child and only 

 survivor of a familv of twelve 



