The year is divided into 12 calendar months, as follows:

When any year can be divided by 4 without a remainder, it is called leap year, in which February has 29 days.

CIRCULAR MEASURE.

Circular measure is used in measuring circles, latitude and longitude, and in computing the revolution of the earth and other planets round the sun. Its denominations are, the circle, c.; the sign, s.; the degree, °; the minute,'; and the second, ".

A sheet folded in two leaves is called a folio. A sheet folded in four leaves is called a quarto, 4to. A sheet folded in eight leaves is called an octavo, or 8vo.

A sheet folded in twelve leaves is called a duodecimo, or 12mo.

A sheet folded in eighteen leaves is called an 18mo.