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Weights and Measures: Julian

The length of the solar year 1880 was 365 da., 5 hr., 48 m., 47 sec., which is nearly one quarter of a day longer than the common year. On the supposition that 3654 days was the true solar year, Julius Cæsar introduced a calendar in which every year exactly divisible by 4 (every fourth year) included 366 days, called leap year. The error of the Julian calendar amounts to 3.1142 days in four centuries. To correct the error, Pope Gregory XIII, in 1582, modified the Julian calendar by making three of the centennial years in cvery four centuries common years and one a leap year. Hence every year that is divisible by 4 and is not a centennial year is a leap year, and every centennial year that is divisable by 400 is a leap year. The year 1900 will be a common year, and the year 2000 a leap year.

Pendulum.-Any weight suspended so as to swing freely under the action of gravity is called a pendulum. Scientific investigation of the swing of the pendulum has proved that the time of the vibration of the pendulum is in proportion to the square root of its length; that is, a pendulum which vibrates once in a second must be four times as long as one which vibrates once in half a second, sixteen times as long as one which vibrates in one fourth of a second, and so on. It has been further shown that the time of the vibration is independent of the length of the arc, or the distance through which the pendulum swings, so long as the arc is comparatively small. This is what gave rise to the application of the pendulum to the regulation of timepieces.

The attraction of gravity which causes the vibration of the pendulum depends upon the distance of a body from the center of the earth. The earth being flattened at the poles, this distance is greater at the equator and less at the poles. Hence the WEIGHTS AND MEASURES same pendulum will vibrate faster at the poles than at the equator. Hence the pendulum is used to determine the force of gravity at various points on the earth's surface. And the length of a pendulum vibrating seconds under stated conditions is now the accepted standard of length in Great Britain and the United States.

In the vicinity of New York a pendulum vibrating once in a second is 39 inches long.

To shorten the pendulum of a clock makes it run faster; to lengthen it makes it run slower.

Measuring Temperature. We commonly use a thermometer known as Fahrenheit's.