PULL OF THE MOON.

Auckland Star, Volume LXVI, Issue 170, 20 July 1935, Page 9 (Supplement)

PULL OF THE MOON.

DRAGS CONTINENTS APART

HOW EARTH CRUST EXPANDS

REMARKABLE MEASUREMENTS.

Ever since it became known in the last century that the moon pulls up not only the waters of the ocean but the rocks as well, measurements of solid tides have been made by the most accurate methods available. They are of the highest scientific importance these measurements. They reveal much about the crust—how strong it is, liowit comports itself relatively to the interior.

For some years Professor Harlan T. Stetson, director of Perkins Observatory, Ohio Weselcyan University, has been studying this effect of the moon on the earth. Recently he flashed the news abroad that the moon actually pulls America and Europe apart and then brings them together again. He had long suspected as much. Now he was certain. Associated with him in this inquiry.was Dr. A. L. Loomis, a banker three days in the week and a physicist the other four. A generation ago it was known that the tides of the sea do not rise to the theoretical height. The reason is that the earth's crust is not rigid, but that it is pulled up as if it were solid steel. Hence as the moon rises and sets, the solid ground beneath us also bulges, though not so much as the water of the sea. North of the equator latitudes ought to be just a trifle higher when the moon nears the meridian. Careful measurements independently made by Dr. F. E. Ross s.nd by Dr. Stetson, to mention but two scientists, show that there is indeed a creeping of the ground and that this creeping agrees with the moon's positon. Now this creeping should manifest, itself not only north and south but e;.st and west. Hence longitude should also bo affected by the moon as it rises and sets. Longitude is calculated by comparing the time of day at two different places. Accurate clocks are therefore necessary and a method of transmitting and receiving time signals by telegraph or radio.

This is where Dr. Loomis comes in. Time-keeping is one of his scientific hobbies. In his private laboratory are three Shortt clocks, probably the most accurate mechanical timepieces known.

With the aid of the clocks Dr. Loomis began to make time measurements. He found, of course, that the pendulum bobs swung at a rate that varied with the moon's position. When the moon was shining on the opposite side of the earth its attraction was added to that of the earth so that a change in rate of four-thousandths of a second was brought about. All this was no more than any physicist would exiieet. But when Loomis compared The time signals telegraphed at the same instant from distant observatories he was perplexed. The signals that come from the Navy clock at Arlington and from Rugby, England (Greenwich time) showed a regular rise and fall in error after all correction had been made. Loomis told Stetson' about his observation. The latter decided to apply his method of studying the moon's laditude effect and measure any actual shifting of the earth's crust east and west. The result, announced from Cambridge, Mass., leaves no doubt that the discrepancies observed by Loomis are caused bv lunar tides set up in the rocks. The continents at opposite sides of the ocean are being rhythmically pulled apart as much as 32 feet, to slip together again by the same distance. That this is a true east-and-west effect and attributable to the moon follows from the positions of the observatories and stations from which the time signals conic. The errors in time rise and fall between Arlington and Rugby and between Arlington and Bordeaux (east and west), but not between .Rugby and Bordeaux (north and south).

How can the solid earth's crust slip back and forth by a total of l>3 feet without breaking? "The distance is the equivalent of stretching a yard of rock by only one part in a hundred thousand," explains Dr. Stetson, "or less than 0.0004 of an inch, an amount well within the elastic limit of solid granite."