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THOMPSON'S COAST PILOT. 138 the United States Army, when a captain, by Major Lachlan, Charles Whittlesey, Esq., and others. The observations con- tained in their memoirs have, however, been directed chiefly to investigations of the extent of the secular and annual varia- tions 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 fluctua- tions which take place on these inland seas. In the specula- tions indulged in by some of these writers; a slight lunar tide 'is sometimes suspected, then again such an influence on the swelling and receding waters is doubted, and their disturbance is attributed to the varying courses and forces of the winds. 'But we have nowhere seen that any systematic course of observation 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 siatieslosl at Chicago, by the orders of the Government, and charged with the direction of the harbor improvements 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, projects into the lake, entirely beyond the mouth of the Chicago River, and altogether out of the reach of any influence from the river current, upon the fluctuations of the tide-gauge. It was the fluctuations of the lake surface alone that could affect the readings of the tide- gauge. 3 'On the first day of September, 1854, a course of observa- tions was commenced on this tide-gauge, and continued at least once a day, until the 31st day of December, inclusive, 1858. 18