FORCE OF GRAVITY. The force of gravity finds expression in that law of physics which declares that every mass is attracted by every other mass with a force varying di rectly as the product of the masses, and in versely as the square of their distances from one another. In the matter of movable bodies upon the earth's surface the term gravity has been given in a restricted sense to the pull which the mass of the earth exerts upon a body near the earth and free to move toward it, or, as we say, a falling body. Under the law quoted the falling body attracts the earth up ward in the proportion of its mass, but the effect is so infinitesimally small that it cannot be considered. It is found that gravity acts upon a body 'allowed to fall from a height with a pull that is uniform within experimental dis tances at the same latitude, and that this pull is greater the nearer we are to the centre of the earth; that is, the pull is greater at the poles than at the equator, because the distance from the poles to the earth's centre (3949.790 miles) is less than from the equator to the centre (3963225 miles). The device which scientists have made use of to determine the force of gravity at different points on the earth's surface is the which, of course, swings because of the action of gravity. (See PENDULUM). Where the pull of gravity is greatest, a pendulum of a given length will swing faster than where it is less: that is, a pendulum of a certain length will swing faster at the poles than at the equator. The procedure, therefore, is to select the length of pendulum which will beat seconds of time at every place of investigation. Then, from the equator as we approach the poles the pendulum to beat exactly one second at each swing must obviously be continually lengthened, and from these changing lengths may be calculated the force of gravity which necessitated the changes. The following table shows the lengths in inches of the second pendulum at latitudes five degrees apart, from the equator to the poles (north or south), and the resulting value for the accelerating pull of gravity per second upon a falling body.
Equator, 39.0131 inches: 32.0875 feet per second 5° 39.0152 inches: 32.0888 feet per second 10° 39.0200 inches: 32.0927 feet per second 15° 39.0274 inches: 32.0989 feet per second 20° 39.0378 inches: 32.1074 feet per second
23° 39.0506 inches: 32.1178 feet per second 30° 39.0652 inches: 32.1299 feet per second 35° 39.0816 inches: 32.1433 feet per second 40° 39.0990 inches: 32.1576 feet per second 45° 39.1169 inches: 32.1724 feet per second 50° 39.1348 inches: 32.1871 feet per second 55° 39.1524 inches: 32.2015 feet per second 60° 39.1687 inches: 32.2150 feet per second 65° 39.1835 inches: 32.2271 feet per second 70° 39.1962 inches: 32.2377 feet per second 75° 39.2067 inches: 32.2462 feet per second 80° 39.2143 inches: 32.2525 feet per second 85° 39.2190 inches: 32.2564 feet per second 90° 39.2206 inches: 32.2577 feet per second The above values are for sea-level at the latitudes noted. For localities above the sea level the velocity will be 0.0002 for each 1,000 feet of elevation. As a rule, the force of gravity is a little less than the value given for places far inland, and a little more for places directly on the seacoast. The theoretical length of the pendulum in feet is expressed by the formula 325114 [1 0.005302 sin' 43-0.000007 sin' 2 This is the length at the sea-level, standing for the latitude north or south of the equator.
The acceleration due to gravity at the places named below are from figures published by the Smithsonian Institute at Washington.
Calais, Mains - 32.1728 feet per second New York City - 32.1612 feet per second Washington. D. C. - 32.1558 feet per second Charleston. S. C.- 32.1372 feet per second St. Georges. Bermuda - 32.1446 feet per second Key West, Fla.- 32.1184 feet per second New Orleans - 32.1883 feet per second Kansas City, Mo.- 32.1518 feet per second Denver. Colo.- 32.1393 feet per second j Pike's Peak - 32.1178 feet per second Salt Lake City -32.1462 feet per second San Francisco - 32.1528 feet per second Port Simpson, B. C.- 32.2000 feet per second Yakutat Bay. Alaska - 32.2122 feet per second Fort Egbert, Alaska - 32.2237 feet per second Honolulu - 32.1184 feet per second Tokio - 32.1182 feet per second Sidney, Australia - 32.1433 feet per second Singapore - 32.0892 feet per second Cape Town - 32.1395 feet per second Pampaluna, Spain - 32.1633 feet per second Geneva, Switzerland - 32.1723 feet per second Berlin - 32.1935 feet per second Paris -32.1837 feet per second Kew. England - 32.1915 feet per second Spitsbergen - 32.2528 feet per second