Evening Republican, Volume 18, Number 192, Rensselaer, Jasper County, 15 August 1914 — EXPLORING the Center of the Earth [ARTICLE+ILLUSTRATION]

EXPLORING the Center of the Earth

By Robert H.Moulton

HERE is a man in Chicago who can measure one-five-millionth of an inch —a distance amounting to one-fiftieth of the smallest distance revealed -by a theoretically perfect microscope. He can rule on a piece of polished glass, one inch wide, 50,000 straight, parallel lines, equally spaced.

He has determined the length of the standard meter so accurately that* his figures cannot be subject toa fault exceeding more than one part in 2,000,000. He has measured the rate at which light travels with a possibility of error not more than one-fortieth of one per cent of the quantity measured—and light flies 186,330 miles a second •—and, as a crowning achievement, he has determined the rigidity of the earth. This man is the first American to receive the Nobel prize in science and the only American who has ever received the Copley medal of the Royal Society of London. Despite achievements that are staggering In their significance, this man's name is little known outside of scientific circles. He is Albert Abraham Michelson, Ph. D., Sc. D., LLD., professor and head of the department of physics at the University of Chicago. Professor Michelson’s experiments to deter-

mine the rigidity of the earth are Intensely Interesting. Science has long needed to know the physical properties of this globe. It is impossible to learn this directly, as the deepest mines yet sunk penetrate less than two miles below the surface, a distance proportionately no greater than the thickness of the varnish on a two-foot globe. The Interior of the ..earth is believed to be intensely hot. This theory is based on the fact that molten lava is thrown forth by erupting volcanoes. Also, in descending a mine, there is a rise in temperature, amounting to 50 degrees per mile of descent If this rate of Increase Is constant, the temperature at only 100 miles down is above the melting point of all substances under conditions as they exist on the surface of the earth. However, despite the high temperature, the interior of the earth may be held in solid state by the tremendous pressure to which it Is subjected. Under the now accepted theory of the celestial mechanics, scientists assume that a heavenly body Is held In its course by the attractive force exerted by the other heavenly bodies on all sides of It 'ln this way is determined the earth’s course around the sun and the motion of the entire solar system through space. Assuming that the earth is not a solid mass, scientists have long struggled to discover how it resisted the attractive forces exerted by other planets and stars —whether as a viscous mass or as a perfectly elastic body. They have • long known that the earth did resist these forces in some degree. The ocean tides which sweep our shores twice daily are proof of this. It has long been known that the tides are caused by the attraction of the sun and the moon. If the earth offered no resistance to this attraction, the whole earth would respond quickly to it and there would be no tides. On the other hand, if the earth were a perfectly rigid body, it would resist this attraction completely; and the tides would reach their maximum height The amount that the tides fall short of their theoretical maximum height would measure the degree of rigidity which the earth possesses. The next step was to determine the actual height of the tides. This long proved the stumbling block. If shore lines were perfectly straight and the floor of the ocean perfectly level, the height of the tides could be measured directly; but crooked shore lines and shelving beaches resist the motion of the tides and make It impossible to determine their height with the accuracy demanded by science. Sir George Darwin made elaborate experiments to determine the height of the tides, but was obliged to give up the problem in despair. Professor Michelson solved this dlfliculty'-by laying two lengths of pipe, each five hundred feet long, and measuring the rise and fall of the water iu them. One length of pipe was laid north and south, and the other length east and west, in order to measure the tides in both directions. The pipes were burlad six feet under ground to obtain a uniform temperature. At both ends of the pipes tees were Inserted having glass windows for observatory purposes. The pipes were half filled with water; and the changes in the height of the water were obtained by measuring through a microscope the distance between a pointer inserted just under the surface of the water and tho bv*ie of the pointer reflect, Ad above tie water.

The maximum tides in these pipes did not exceed one-thousandth of an inch; but so perfect was the apparatus and so accurate the readings by Professor Michelson that all the variations in the tides were accurately determined. Tides are complex things. Their height varies with the position and distance of both the sun and the moon and, therefore, is never the same two'days in succession. Professor Michelson’s experiments revealed 30 of these variations, which corresponded almost exactly with the variations obtained theoretically by computing the variations in the attractive forces exerted by the sun and the moon. The practical correspondence of the actual height of the tides with the theoretical height proved that the earth through and through is as rigid as steel and that it yields to outside forces as a perfectly elastic body and not as a viscous mass. This experiment reveals the imagination and the striking originality of Professor Michelson. The first achievement to bring his name to the attention of the scientific world was his accurate determination of the velocity of light, accomplished also after .overcoming tremendous experimental difficulties Light is the fastest thing in nature; ft represents the absolute limit of speed. After four years of work and study, Professor Michelson announced that light travels with a velocity of 186,330 miles per second. The maximum error in this figure does hot exceed onefortieth of one per cent. On the subject of spectrum analysis, Professor Michelson has devoted many of the best years of his life. Spectrum analyses are obtained by means of the spectroscope. Every substance when heated emits a characteristic light By means of the spectroscope this light is analyzed and the elements giving off the light are thereby revealed. The spectroscope has X enabled scientists to determine the -elements in far distant stars. It has made possible tremendously important discoveries concerning the nature of atoms, the minute particles of which all matter is composed. The difficulties of spectrum analysis will be realized when it fa learned that a single atom of sodium emits 800,000,000,000 vibrations per second of two slightly different kinds of light Professor Michelson was engaged tn spectrum analysis very long before he Improved the spectroscope, calling the improved type an echelon spectroscope. This wonderful machine divides light into its various constituents and makes possible their separate analysis. The echelon spectroscope uses a glass grating —a piece of highly polished glass on which is ruled from 15,000 to 50,000 straight equally-spaced lines to the inch. To make these gratings Professor Michelson Invented a ruling engine that is the most accurately constructed mechanical device in the world. It is operated in a room the temperature of which Is kept constant to wlthlu one-hundredth of a degree. To assist in analyzlng the lines of the spectrum into their fundamental constituents. Professor Michelson invented the "harmonic analyzer,” a machine as complicated and as delicate as the linotype machine. By its use an assistant can id a few minutes make calculations that would take a skilled computer weeks to accomplish. Scientists have long endeavored to determine the absolute motion of the earth through space. It is known that the earth swings around the sun

and that the'entire solar system is moving toward the constellation Hercules at the rate Of 12 miles . per second, or 400,000,000 miles per year. However, as scientists have not yet been able to measure the motion of Hercules, they still do not know the absolute motion of the earth. In 1880 Professor Michelson attacked the problem of determining the motion of the earth with reference to the ether, the aH-pervading medium that fills Interstellar space. • All of us have noticed, that, when walking through the rain, although it is actually falling vertically, it seems to be falling at an angle, the degree of this apparent deflection depending upon the speed with which we have moved. Looking out the window of a fast-moving train, scientists have noticed a similar deflection in the angle of the light coming to the earth from some far distant star. As the medium that carries the light between heavenly bodies is the ether, scientists argue that the deflection is due to the relative motion of the earth through the ether. * Professor Michelson eventually overcame the tremendous experimental difficulties in connection with this problem; but no motion of the earth with respect to the ether was found. This result came as a profound surprise to the entire scientific world. In order to solve this problem Professor Michelson invented a most marvelous instrument, which he called the “interferometer.” This instrument is 50 times more powerful than an ab" solutely perfect microscope would be. The microscope’s power is limited by the length of a light wave; and the smallest distance it can reveal is one-half a wave length, or one hundred-thou-sandths of an inch. By utilizing the properties of light in another ipanner, the interferometer can reveal distances equivalent to one five-millionth of an inch. The microscope has been of immense value both In scientific work and in practical life; and the invention of the Interferometer, an instrument 50 times more powerful, is in itself an achievement that should win for Professor Michelson undying fame./He this instrument to aid him in measuring the standard- meter, the foundation of the metric system, in terms of infinite exactitude and in a manner that will make this unit perpetual. The original meter length is carefu’lv preserved at Paris; .but scientists have long worried over the possibility of its destruction. In 1893 an International commission On weights and measures asked Professor Michelson to devise some method by which the meter length could be accurately reproduced. The meter is theoretically one fortymillionth of the earth’s circumference; but this definition is "not accurate enough for scientific purposes. Professor .Michelson announced the length of the meter in terms of cadmium light waves, with a maximum error of one part tn two million. This definition will always enable scientists to reproduce the meter accurately, as long as the earth exists. These are the most striking achievements of America’s greatest scientist. Any one of them is sufficient to perpetuate a man’s name In the annals of science. Tho result of Professor Michelson’s experiments with reference to the motion of the earth has raised questions that it will take science many years to answer satisfactorily; and his determination., of the rigidity of the earth has made possible further and more wonderful progres' in the sphere of ce’cstial mechanics