and that 235 lunations are exactly equal to nineteen solar years. It could
not therefore long continue to preserve its correspondence with the
seasons, or to indicate the days of the new moons with the same accuracy.
About the year 730 the venerable Bede had already perceived the
anticipation of the equinoxes, and remarked that these phenomena then took
place about three days earlier than at the time of the council of Nicaea.
Five centuries after the time of Bede, the divergence of the true equinox
from the 21st of March, which now amounted to seven or eight days, was
pointed out by Johannes de Sacro Bosco (John Holywood, _fl._ 1230) in his
_De Anni Ratione_; and by Roger Bacon, in a treatise _De Reformatione
Calendarii_, which, though never published, was transmitted to the pope.
These works were probably little regarded at the time; but as the errors of
the calendar went on increasing, and the true length of the year, in
consequence of the progress of astronomy, became better known, the project
of a reformation was again revived in the 15th century; and in 1474 Pope
Sixtus IV. invited Regiomontanus, the most celebrated astronomer of the
age, to Rome, to superintend the reconstruction of the calendar. The
premature death of Regiomontanus caused the design to be suspended for the
time; but in the following century numerous memoirs appeared on the
subject, among the authors of which were Stoffler, Albert Pighius, Johann
Schoener, Lucas Gauricus, and other mathematicians of celebrity. At length
Pope Gregory XIII. perceiving that the measure was likely to confer a great
_eclat_ on his pontificate, undertook the long-desired reformation; and
having found the governments of the principal Catholic states ready to
adopt his views, he issued a brief in the month of March 1582, in which he
abolished the use of the ancient calendar, and substituted that which has
since been received in almost all Christian countries under the name of the
_Gregorian Calendar_ or _New Style_ The author of the system adopted by
Gregory was Aloysius Lilius, or Luigi Lilio Ghiraldi, a learned astronomer
and physician of Naples, who died, however, before its introduction; but
the individual who most contributed to give the ecclesiastical calendar its
present form, and who was charged with all the calculations necessary for
its verification, was Clavius, by whom it was completely developed and
explained in a great folio treatise of 800 pages, published in