“The Julian rule made every fourth year, without exception, a bissextile. This is, in fact, an over-correction; it supposes the length of the tropical year to be 365¼ d. , which is too great, and thereby induces an error of 7 days in 900 years, as will easily appear on trial. Accordingly, so early as the year 1414, it began to be perceived that the equinoxes were gradually creeping away from the 21st of March and September, where they ought to have always fallen had the Julian year been exact, and happening (as it appeared) too early. The necessity of a fresh and effectual reform in the calendar was from that time continually urged, and at length admitted. The change (which took place under the Popedom of Gregory XIII ) consisted in the omission of ten nominal days after the 4th of October, 1582 (so that the next day was called the 15th, and not the 5th), and the promulgation of the rule already explained for future regulation.”