The annexed figure represents a perpetual calendar, which any one can construct for himself, and which permits of finding the day that corresponds to a given date, and conversely.

The apparatus consists of a certain number of circles and arcs of circles divided by radii. The ring formed by the two last internal circles is divided into 28 equal parts, which bear the names of the week, the first seven letters of the alphabet in reversed order, and two signs X. The circle formed by the external circumference of the ring constitutes the movable part of the apparatus, and revolves around its center. Two circular sectors, which are diametrically opposite, are each divided into seven parts and constitute the fixed portions. In the divisions of the upper sector are distributed the months, according to the order of the monthly numbers. In the other sector the days of the month are regularly distributed. In order to render the affair complete, a table is arranged upon the movable disk for giving the annual numbers, or rather, in this case, the annual letters. The calendar is used as follows: Say, for example, we wish to find what days correspond to the different dates of August, 1885; we look in the table for the letter (D) that corresponds to this year; then we bring this letter under the given month (August) and the days marked upon the movable disk corresponding to the dates sought, and it only remains to make a simple reading.

PERPETUAL CALENDAR.

PERPETUAL CALENDAR.

It will be seen that the leap-years correspond to two letters. We here employ the first to Feb. 29 inclusive, and the second for the balance of the year. The calendar may be made of cardboard, and be fixed to wood. - La Nature.