GREGORY. 
future, he ordered that three days should 
be abated in every four hundred years by 
reducing the leap year at the close of each 
century for three successive centuries 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 Britain 
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 European 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- 
drew’s, 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 Gre- 
gory, 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 mathematical 
and mechanical knowledge. This mathe- 
matical genius was hereditary in the family 
of the Andersons, and from them it seems 
to have been transmitted to their descend- 
ants 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 cen- 
tury, and published there several valuable 
and ingenious works. The mother of 
James Gregory inherited the genius of hep 
family ; and observing in her son, while yet 
a child, a strong propensity to mathematics, 
she instructed him herself in the elements 
of that science. His education in the lan- 
guages 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 delight- 
ed 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 principal 
study of young Gregory, who soon began 
to make improvements upon their disco- 
veries in Optics. The first of these im- 
provements was the invention of the re- 
flecting telescope ; the construction of 
which instrument he published in his “ Op- 
tica Promota,” in 1663, at twenty-four 
years of age. This discovery soon attract- 
ed the attention of the mathematicians, 
both of our own, and of foreign countries, 
who immediately perceived its great impor- 
tance to the sciences of optics and astrono- 
my. But the manner of placing the two 
specula upon the same axis appearing to 
Newton to be attended with the disadvan- 
tage of losing the central rays of the larger 
speculum, he proposed an improvement on 
the instrument, by giving an oblique posi- 
tion to the smaller speculum, and placing 
the eye-glass in the side of the tube. It is 
observable, however, that the Newtonian 
construction of that instrument was long 
abandoned for the original, or Gregorian, 
which is now always used when the instru- 
ment is of a moderate size ; though Her- 
schell has preferred the Newtonian form for 
the construction of those immense teles- 
copes, which he has of late so successfully 
employed 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 artists 
to grind a plate of metal for the object spe- 
culum into a true parabolic concave, which 
tlje design required, he was much discou- 
raged with the disappointment ; and, after 
a few imperfect trials made with an ill-po- 
lished spherical one, which did not succeed 
to his wish, he dropped the pursuit, and re- 
solved to make the tour of Italy, then the 
mart of mathematical learning, that he 
might prosecute his favourite study with 
greater advantage. And the University of 
Padua, being at that time in high reputa- 
tion for mathematical studies, Mr. Gregory 
fixed his residence there for some years. 
Here it was that he published, in 1667, 
“ Vera Circuli et Hyperbolae Quadratura 
in which he propounded another discovery 
ot his own, the invention of an infinitely 
converging series for the areas of the circle 
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 
