GllEGORY. 



cd in every four hundred years, by re- 

 ducing 1 the leap year at the close of 

 each century, for three successive cen- 

 turies, to common years, and retaining 

 the leap year at the close of each fourth 

 century only. 



This was at that time esteemed as 

 exactly conformable to the true solar 

 year, but it is found not to be strictly 

 just, because that in four hundred years 

 it gets one hour and twenty minutes, 

 and consequently in 7200 years a whole 

 day. 



The greatest part of Europe have long 

 used the Gregorian style : but great Bri- 

 tain retained the Julian till the year 1752, 

 when, by act of parliament, this style was 

 adjusted to the Gregorian ; since which 

 time Sweden, Denmark, and other Eu- 

 ropean states, who computed time by 

 the Julian account, have followed this 

 example. 



GREGORY (JAMES), professor of ma- 

 thematics, first in the university of St. An- 

 drews, and afterwards in that of Edin- 

 burgh, was one of the most eminent ma- 

 thematicians of the seventeenth century. 

 He was a son of the Rev. John Gregory, 

 minister of Drumoak, in the county of 

 Aberdeen, and was born at Aberdeen, in 

 November 1638. His mother was a 

 daughter of Mr. David Anderson, of Fin- 

 zaugh, or Finshaugh ; a gentleman who 

 possessed a singular turn for mathemati- 

 cal and mechanical knowledge. This 

 mathematical genius was hereditary in the 

 family of the Andersons, and from them 

 it seems to have been transmitted to 

 their descendants of the names of Gregory, 

 Reid, &c. Alexander Anderson, cousin 

 german of the said David, was professor 

 of mathematics at Paris in the beginning 

 of the 17th century, and published there 

 several valuable and , ingenious works. 

 The mother of James Gi'egory inherited 

 the genius of her family; and observ- 

 ing in her son, while yet a child, a strong 

 propensity to mathematics, she instruct- 

 ed him herself in the elements of that 

 science. His education in the languages 

 he received at the grammar-school of 

 Aberdeen, and went through the usual 

 course of academical studies in the Ma- 

 rischal college; but he was chiefly de- 

 lighted with philosophical researches, 

 into which a new door had lately been 

 opened by the key of the mathematics. 

 Galileo, Kepler, Des Cartes, &c. were 

 the great masters of this new method ; 

 their works therefore became the princi- 

 pal study of young Gregory, who soon 



began to make improvements upon their 

 discoveries in Optics. The first of these 

 improvements was the invention of the 

 reflecting telescope ; the construction of 

 which instrument he published in his 

 " Optica Promota," in 1663, at twenty- 

 four years of age. This discovery soon 

 attracted the attention of the mathemati- 

 cians, both of our own and of foreign 

 countries, who immediately perceived its 

 great importance to the sciences of op- 

 tics and astronomy. But the manner of 

 placing the two specula upon the same 

 axis appearing to Newton to be attended 

 with the disadvantage of losing the cen- 

 tral rays ef the larger speculum, he pro- 

 posed an improvement on the instrument, 

 by giving an oblique position to the small- 

 er speculum, and placing the eye-glass 

 in the side of the tube. It is observable, 

 however, that the Newtonian construc- 

 tion of that instrument waslong abandon- 

 ed for the original, or Gregorian, which 

 is now always used when the instrument 

 is of a moderate size ; though Herschell 

 has preferred the Newtonian form for the 

 construction of those immense telescopes, 

 which he has of late so successfully em- 

 ployed in observing the heavens. 



About the year 1664, or 1665, coming 

 to London, he became acquainted with 

 Mr John Collins, who recommended him 

 to the best optic glass-grinders there, to 

 have his telescope executed. But as this 

 could not be done, for want of skill in the 

 artist to grind a plate of metal for the 

 object speculum into a true parabolic con- 

 cave, which the design required, he was 

 much discouraged with the disappoint- 

 ment,and,after a few imperfect trials made 

 with an ill-polished spherical one, which 

 did not succeed to his wish, he dropped 

 the pursuit, and resolved to make the 

 tour of Italy, then the mart of mathemati- 

 cal learning, that he might prosecute his 

 favourite study with greater advantage. 

 And the University of Padua being at 

 that time in high reputation for mathe- 

 matical studies, Mr. Gregory fixed his 

 residence there for some years. Here 

 it was that he published, in 1667, " Vent 

 Circuli et Hyperbolae Quadrature?" in 

 which he propounded another discovery 

 of his own, the invention of an infinitely 

 converging series for the areas of the cir- 

 cle and hyperbola. He sent home a copy 

 of this work to his friend Mr. Collins, who 

 communicated it to the Royal Society, 

 where it met with the commendations of 

 Lord Brounker and Dr. Wallis. He re- 

 printed it at Venice the following year, 

 to which he added a new work, entitled 



