For calculating long intervals of time it was found desirable to eliminate the months and years, and number the days consecutively. Hence one such numbered day is identified by the prefix J.D., meaning Julian Day. (v. Day.)
This table of Julian Days is a convenience in computing the num- ber of elapsed days between any two dates. Merely set down the J.D. for the two days and subtract: the difference will be the number of elapsed days. For dates that are separated by only 2 or 3 years, it will be necessary to use only the last three or four digits. These tables can be applied to any years, if care is exercised to see that a table for a bissextile year is used for a bissextile year, and one for a common year is used for a common year.
