WEIGHING THE EARTH

Taranaki Daily News, 9 October 1928, Page 15

WEIGHING THE EARTH

SCALE THREE FEET HIGH USED. Science is now engaged in the heaviest job that can be undertaken—that of weighing the earth with a new scale that is only three feet tall! The result is difficult to convey except in mighty figures. One investigator attempts to simplify calculations by explaining that if it were possible for a man to construct a globe 800 ft in diameter, and to place upon any one point of its surface an atom 1-4380th of an inch in diameter and l-129th part of an inch in height, it would correctly denote the proportion man bears to the earth on which he stands.

The leader of this fascinating feat that so grips the imagination is Dr. Paul R. Heyl, a physicist of the United States Bureau of Standards in Washington, D.C., who is now stationed in a laboratory cave 35ft underground. Dr. Heyl is equipped with & wonderful new apparatus invented and perfected more than a year ago. Dr, Heyl’s task will take several months, but in the end he expects to arrive at a measurement which will stand as the last word in accuracy for years.

That man, a mere speck standing on a globe 8000 miles in diameter, should be able to weigh that globe, seems almost beyond belief. Yet, actually, the way in which Dr. Heyl does it is fairly simple and understandable. How he merely applies the law of gravitation, discovered by Isaac Newton more than two centuries ago is set forth in the Popular toward every other particle with a force varying directly as the product Science Monthly by Edwin Ketchum.

This law states that every particle of matter in the universe is attracted of their masses and inversely as the square of the distance between them. In other words, the force of gravitation acting between two bodies depends on two factors—their distance apart and their mass or weight. It must follow, then, that if the value of this force is known, the mass of one of the bodies, and the distance between the two, then the mass of the other body can be calculated.

This is exactly how Dr. Heyl calculates the mass of the earth. He asks the question: ‘How much mass must the earth have to exert the attraction it does upon a body at its surface, 4000 miles distant from its centre. And he finds the answer to this question by first measuring the value of the force of attraction—a value which is known as the “constant gravitation.” This force of gravitation keeps the planets on their place in the heavens, and it is the most vital, yet most mysterious, force in the universe. It holds the stars in their courses. Without it, everything on the earth would fly helter-skelter through space. Dr. Heyl tackles the problem first by placing, side by side, two small objects which can be handled readily, and measuring the gravitational attraction between them. Then he applies the result proportionately to larger bodies, such as the earth.

To obtain the greatest accuracy, Dr. ■Heyl does his “weighing” in a small room beneath the earth’s surface. This not only assures the constant temperature necessary for the use of delicate instruments, but it prevents the upsetting of his calculation by the gravitational attraction of moving objects, such as automobiles and people. If you should visit this underground laboratory, you would be surprised to find that his earth-weighing “scale” is an apparatus only about three feet tall. It consists of an instrument known as a “torsion balance,” which measures the gravitational attraction between little glass balls weighing about two ounces each and steel cylinders weighing 1401 b. In a vacuum within an iron ease hangs a light aluminium rod, suspended in horizontal position from an exceedingly fine tungsten wire; and at each end of the rod is a glass ball. This pendulum arrangement is made to swing back and forth, twisting and untwisting the wire. On opposite side., of the iron case, and as close as possible to the b Ils, hang the two cylinders. The attraction between cylinders and balls affects the swinging time of the pendulum. Thus, when the cylinders are shifted to positions somewhat farther from the balls, the gravitational attraction is correspondingly lessened, and the time of swing is changed accordingly. By measuring this difference in time with a moving beam of light on a scale, Dr. Heyl calculates ti.e actual value of the attraction.

Thus with this tiny measurement completed, weighing the earth becomes simply a problem in proportion.