The connexion between the days or numbers of the week which designate the beginning of the year, and the four initial or first days of the series of five, is so intimate that it is very difficult to intercalate an additional day for the bissextile, without disturbing that correlative order of the initials which is constantly followed in the denomination of the years, and forms their indictions, or weeks.
"Incidents of Travel in Yucatan, Vol. I."
John L. Stephens
As often as he meets with new groups, he must ascertain by superposition their age relatively to those first examined, and thus learn how to intercalate them in a tabular arrangement of the whole.
"The Student's Elements of Geology"
Sir Charles Lyell
By this reformation, says Dion Cassius, all error was avoided except a very small one, and he adds, that to correct the accumulations of this error, it would only be necessary to intercalate one day in 1461 years.
"Plutarch's Lives Volume III."
Plutarch