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are able to publish in the present issue of the the address given by Mr. G. K. Gilbert as retiring president of the American Association for the Advancement of Science. The problem that he discusses is one of the most pressing for scientific workers, while at the same time it is of interest to everyone, and the address is at once an important contribution to the subject and an exposition that all can understand. The mathematical physicists find that as an abode fitted for life the earth can not be allowed a history indefinitely long—not longer perhaps than 20,000,000 years—while the geologists with equally strong arguments claim a much greater antiquity. The biologists are also concerned, owing to the time taken up by the processes of evolution, and their facts and interests range them with the geologists rather than with the physicists. The man not versed in science would also prefer to assign a long history to the earth, for while he may be ready to let the 'dead past bury its dead,' he looks forward even to the distant future, and the shorter the past history of the earth the less the time it will continue to be habitable. We have thus a question in the solution of which all the sciences are concerned, and one possessing a dramatic interest that appeals to everyone. The unity of science is well illustrated by such a problem. It was the subject of the address of the retiring president of the Association, a geologist; it might be taken as the subject for the address of the newly elected president, a biologist and student of the processes of evolution; and it is one to which the president of the meeting, a mathematical physicist, has given special attention.

who presided over the New York meeting of the Association, is professor of mechanics and mathematical physics and dean of the Faculty of Pure Science in Columbia University. He was born at Rochester, Oakland County, Michigan, July 21, 1849, and spent his early life on a farm with the exception of about two years of experience in mercantile and manufacturing pursuits. He was prepared for college at the Rochester Academy, entered the University of Michigan in 1868, and was graduated in 1872 with the degree of C. E. Twenty years later the same institution conferred upon him the degree of Ph. D. While yet an undergraduate he entered the U. S. Lake Survey, and immediately after graduation he was appointed assistant engineer in that service. He was employed in the astronomical and geodetic work of the Lake Survey until its completion in 1882. He then accepted the position of assistant astronomer to the U. S. Transit of Venus Commission and accompanied the expedition of Prof. Asaph Hall, U. S. N., to San Antonio, Tex., to observe the transit of December, 1882. He remained with the Transit of Venus Commission until 1884, when he resigned in order to take the position of astronomer in the U. S. Geological Survey. After four years of service in this bureau he resigned to accept the position of assistant in the U. S. Coast and Geodetic Survey. This he held until 1893, when he retired from the public service and accepted the call of Columbia University to the chair of mechanics. In 1895, and again in 1900, he was elected to the deanship of the graduate faculty of pure science in that institution. Professor Woodward has published many papers on subjects in astronomy, geodesy, mathematics and mechanics. He edited, and contributed several chapters to the final report of