122 THK UNIVERSE A VAST SYSTEM OF PARTS where the dial is erected. This change in the design of the sundial corrects for the apparent movement of the sun in a north and south direction. Mechanical Devices. The need arose for an instrument that would measure time both day and night, independently of the sunlight. 1. Tapers graduated into equal parts were once used to indicate time, inasmuch as they burned at a roughly constant rate. 2. The clepsydra was a simple measuring device which depended upon the time required for a given amount of water to trickle through a hole in the bottom of a suitable container. The modern hourglass or sandglass is a variation of the clepsydra. 3. More complicated deinces depended upon the motion of a pointer connected by gears to a float that was raised as the vessel in which it rested was gradually filled with water. 4. Power-driven clocks superseded the water clocks because they removed difficulties involved in maintaining a water supply that would not freeze in the winter and because water clocks could not be used at sea. (In navigation, longitude can be determined 07ily if one knows the time somewhere else.) 5. The modern electric clocks, which are rapidly replacing other types of clocks, are run by the alternating current whose pulsations are checked by master clocks at the powder plants. In reality, then, all electric clocks are merely devices to receive and indicate time signals transmitted by alternating current from a master clock. Most power companies generate 60-cycle current, that is, current which alternates exactly 120 times a second. Inside an electric clock is a tiny motor synchronized with the generators in the powerhouses. The Calendar. Julius Caesar in 45 B.C. introduced the Julian calendar invented by Sosigenes. He used 3653^ days as the year and invented the leap year to take care of the quarter-days. The Julian year is too long by 11 minutes and 14 seconds. In 400 years, this variation w^ould amount to 3 days. In the sixteenth century, this error had mounted to 1 1 days. Pope Gregory, at that time, dropped 10 days from the calendar, but not without considerable opposition. The Gregorian calendar provides that century years are not leap years unless they are divisible by 400, thus making another such radical revision of the calendar unnecessary, because our present year is too long by only 26 seconds. Thus the Gregorian calendar provides for fewer leap years than the Julian calendar.
TIME AND THE CALENDAR 123 The Gregorian calendar was adopted by England in 1752, by Russia in 1917, by Yugoslavia and Rumania in 1919, and by Greece in 1923, at which time 13 days had to be dropped from the calendar. Julius Caesar s calendar provided that all even-numbered months should have 30 days except February, which was to have only 28 days except in leap years, while all odd-numbered months were to have 31 days. The Roman Senate honored Julius Caesar by naming July after him. Later Augustus Caesar had the month of August named after him and changed the length of the month to 31 days in order to have it equal Julius Caesar's month in number of days. This change unbalanced the length of the quarters, so a day was taken from September and from November and added to October and December. Many people believe that we are about due for a new deal as far as the calendar is concerned. Our present calendar, thus handed down to us by the Caesars and Pope Gregory, possesses the following disadvantages: Months, quarters, and half-years are not of equal length and do not contain whole numbers of weeks, thus making calculations of salaries, rents, interest, and other business transactions inaccurate when based on monthly, quarterly, or semi-yearly periods. The calendar is not perpetual, and holidays and other principal events occur on different days of the week from year to year. Many improvements in the calendar have been recommended. of them is One a year of 13 months — 28 days each — the 13th month to be named Sol, and New Year's Day to be the extra day not belonging to any month ; in leap years another day is to be added between February and March. In 325 A.D. the Council of Nice adopted the rule for Easter, which fixes it as the first Sunday after the 14th day of the nearly full moon which occurs on or immediately after March 21. Easter Dates 1942