{Gregorian calendar}, the calendar as reformed by Pope
Gregory XIII. in 1582, including the method of adjusting
the leap years so as to harmonize the civil year with the
solar, and also the regulation of the time of Easter and
the movable feasts by means of epochs. See {Gregorian
year} (below).
{Gregorian chant} (Mus.), plain song, or canto fermo, a kind
of unisonous music, according to the eight celebrated
church modes, as arranged and prescribed by Pope Gregory
I. (called ``the Great'') in the 6th century.
{Gregorian modes}, the musical scales ordained by Pope
Gregory the Great, and named after the ancient Greek
scales, as Dorian, Lydian, etc.
{Gregorian telescope} (Opt.), a form of reflecting telescope,
named from Prof. James Gregory, of Edinburgh, who
perfected it in 1663. A small concave mirror in the axis
of this telescope, having its focus coincident with that
of the large reflector, transmits the light received from
the latter back through a hole in its center to the
eyepiece placed behind it.
{Gregorian year}, the year as now reckoned according to the
Gregorian calendar. Thus, every year, of the current
reckoning, which is divisible by 4, except those divisible
by 100 and not by 400, has 366 days; all other years have
365 days. See {Bissextile}, and Note under {Style}, n., 7.