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.
[Illustration: 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._
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