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Longitude and Time-Table: Greenwich

Watches vary from two beats a second to beats registering fifths of a second. The number of complete oscillations of the pendulum of a clock vary directly as the square of its length.

The great clock of Westminster is regulated electrically from Greenwich, and it seldom varies more than a second in a week. It has a special contrivance for making the first blow of the hour strike exactly on the right time; and the blow on Big Ben is struck with a 400 lb. hammer.

The earliest clocks were sundials, then came the hour glass, then the water clocks. A wheel and weight clock was constructed at Madgeburg in 996. The first watch was a small clock, In 1477, Peter Hele, of Nuremburg, made a clock in the form of an egg which could be carried in the pocket. It required winding twice a day, and varied an hour a day from the correct time. Hele probably invented the fusee spring, but the hair-spring was the invention of Dr. Robert Hooke, an Englishman, in 1658, and the latter was also the first to use a lever escapement in 1666. The use of jewels for the bearing of the pivots was introduced about 1700, and the compensation balance was invented in 1767.

The main wheel of a watch makes four revolutions in 24 hours, 1480 in a year; the second or centre, 24 revolutions in 24 hours or 8760 in a year; the third wheel, 192 in 24 hours, or 70,080 in a year; the fourth wheel-which carries the second hand-1440 in 24 hours, or 525,600 in a year; the fifth or scape-wheel, 12,964 in 24 hours, or 4,731,860 revolutions in a year; while the beats or vibrations made in 24 hours are 388,800, or 141,912,000 in a year.

Difference in Time. When it is just 12 M. at Greenwich the clocks in these cities point as follows:

H. M.

H. M.

Adelaide 9 14 P.M.

Munich o 46 P.M.

Amsterdam O 20 P.M.

New Orleans 5 59 A.M.

Berlin O 54 P.M.

New York 7 4 A.M.

Berne 0 30 P.M.

Paris Ο 9 P.M.

Bombay. 4 52 P.M.

Pekin 7 46 P.M.

Boston 7 18 A.M.

Philadelphia 6 59 A.M.

Brussels o 17 P.M.

Quebec ... 7 15 Α.Μ.

Calcutta. 5 54 P.M.

Rio Janeiro 9 7 A.M.

Capetown I I4 P.M.