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118 THOMPSON'S COAST PILOT. A Lunar Tidal Wave in the North American Lakes. Extract from a paper read by Lieut.-Col. Graham, before the American Association for the advancement of Science, August, 1860. * Much has been written, at various periods, on the fluctuations in the elevation of the surface waters of the great fresh water lakes of North America. Valuable and interesting memoirs have appeared from time to time in the American Journal of Science and Arts, published monthly at New Haven, Connecticut, within the last thirty years, on this, subject, written by the late Brevet Brigadier General Henry Whiting, of the United States Army, when a cap- tain, by Major Lachlan, Charles Whittlesey, Esq., and others. 'The observations contained in their memoirs have, however, been directed chiefly to investigations of the extent of the secular and annual vari- ations in elevation of the surfaces of these lakes. 'The learned Jesuit fathers of the time of Marquette, a period near two centuries ago, and at later periods the Baron de la Hontan, Charlevois, Carver, and others, noticed in their writings the changes of elevation, and some peculiar fluctuations which take place on these inland seas. In the speculations indulged in by some of these writers, a slight lunar tide is sometimes suspected, then again such an influ- ence on the swelling and receding waters 'is doubted, and their dis- turbance is attributed to the varying courses and forces of the winds. | « But we have nowhere seen that any systematic course of ob- servation was ever instituted and carried on by these early explorers, or by any of their successors who have mentioned the subject, giving the tidal readings at small enough intervals of time apart, and of | long enough duration to develop the problem of a diurnal lunar tidal wave on these lakes. The general idea has undoubtedly been that no such lunar influence was here perceptible. "In April, 1854, I was stationed at Chicago, by the orders of the Government, and charged with the direction of the harbor im- provements on Lake Michigan. In the latter part of August of that year, I caused to be erected at the east or lakeward extremity of the North Harbor pier, a permanent tide-gauge for the purpose of making daily observations of the relative heights and fluctuations of the surface of this lake. The position thus chosen for the observations, a a a ih al ert Tae gE a it