Prairie Tube

In Chicago, there dwells a renowned professor named Albert Abraham Michelson. A member of the faculty of the University of Chicago, he has made many a valuable contribution to Science. Born at Strelno, Germany, a son of Samuel Michelson and Rosalie Przlubska, he is a brother of Charles Michelson (rabidly Democratic chief of The New York World's Washington Bureau) and of Miriam Michelson (author). But he graduated from the Naval Academy at Annapolis when these two were still on the Pacific coast, in swaddling clothes.

Albert became an instructor in physics at the Naval Academy, and then continued his studies at Heidelberg. Soon afterward he began to acquire the reputation that won him the Nobel Prize for Physics in 1907 and distinctions and degrees without number. He was, for example, the first to measure the diameter of distant stars.

Yet in the course of many years, he had not given a public lecture. Last week, the President and Trustees of Chicago University persuaded him. They secured the use of a downtown theatre and prevailed upon him to address a large audience consisting mainly of sponsors of the University.

He began with fundamentals, comprehensible to the lay mind, explaining wave-motion by slides and motion pictures of a number of experiments. He showed the properties of water waves and similar mechanical waves. He showed the properties of sound waves. From these, he went on to show the properties of the different but analogous waves of light. All this was to demonstrate the principle on which one of his great inventions--which he has labored 40 years in perfecting--is based.

This instrument is a device for taking very delicate measurements of the speed of light rays. Two rays are used for comparison. It works roughly on the principle that, if two sets of waves are produced and the crest of one is timed to come in the trough of another, the appearance of waves is destroyed. In the case of light, this means a dark place or shadow. When the light rays are received upon a given surface, visible dark lines are formed by the interference of the waves. Using this device in Southern California, last year, experiments were made by Prof. Michelson which measured the speed of light--now given as 186,000 miles a second--with a possible error of only 20 miles per second. A light and the interferometer were placed on one peak. A mirror was placed on a peak 20 miles distant. By receiving rays direct from the light next to it and rays which had travelled 40 miles (from the light to the distant mirror and back), the interferometer showed the light fringes and dark lines of interference from which the speed of light was calculated.

Then Prof. Michelson proceeded to describe an experiment which has been in progress for some months on a prairie just west of Chicago (TIME, Aug. 11). There a rectangle of 12-inch pipe, almost a mile in perimeter, was laid down. Its greater dimension extends from east to west. This pipe was sealed and the air exhausted. Mirrors were placed in the corners so that a beam of light would be reflected completely around it. In one corner an arc light was placed, the beams of which, split by mirrors, were reflected around the rectangle in opposite directions.

If the beams, traveling around the rectangle in both directions, moved at the same rate, the waves would come into the interferometer simultaneously; there would be no interference, hence no dark lines and light fringes on the receiving surface. If the beam going in one direction traveled faster than the beam going in the opposite direction, their waves would arrive at different times; there would be interference, hence black lines and light fringes visible in the instrument. With this second result, it would be apparent that something impeded the light going in one direction--the movement of the earth (as the Einstein theory foretells would be the case) or the drift of the ether (according to the ether drift theory).

Prof. Michelson was nearing the end of his lecture. He told of the difficulties the experimenters encountered. An air leak developed in the pipe and some hundreds of joints had to be repainted. The jars of a train moving more than a mile away disordered the delicate instruments. Much of the work had to be done at night and in the early hours of the morning to avoid mechanical difficulties.

Then the professor explained that the results of the experiment were still provisional--that work was to go on for another month or two. But in no experiment so far had the beams going in opposite directions returned to the interferometer simultaneously. Every time there was interference, light fringes and dark lines supporting both the Einstein theory and the ether drift theory. More accurate observations are still to be made, but Mr. Michelson said in conclusion, referring to Einstein: "There is no question that the tests furnish another striking confirmation of his brilliant work."