My attention has been drawn to the subsidence of the waters of the lakes of Canada by the unusual lowness of Ontario, on the banks of which I lived last year, and by reading the statement of the American writer above quoted, as well as by the fact that in the Travels of Carver, one of the first English navigators on these mediterraneans, who states that a small ship of forty tons, in sailing from the head of Lake Michigan to Detroit, was unable to pass over the St. Clair flats for want of water, and that the usual way of passing them eighty years ago was in small boats. What a useful thing it would have been, if any scientific navigators or resident observers had registered the rise and fall of the lakes in the years since Upper Canada came into our possession! An old naval officer told me that it was really periodical; and it occurred usually, that the greatest depression and elevation had intervals of seven years. Lake Erie is evidently becoming more shallow constantly, but not to any great or alarming degree; and shoals form, even in the splendid roadstead of Kingston, within the memory of young inhabitants. An American revenue vessel, pierced for, I believe, twenty-four guns, and carrying an enormous Paixhan, grounded in the autumn of last year on a shoal in that harbour, which was not known to the oldest pilot. By the bye, talking of this vessel, which is a steamer built of iron, and fitted with masts and sails, the same as any other sea-going vessel, can it be requisite, in order to protect a commerce which she cannot control beyond the line drawn through the centre of the lakes, to have such a vessel for revenue purposes? or is she not a regular man-of-war, ready to throw her shells into Kingston, if ever it should be required? At least, such is the opinion which the good folks of that town entertained when they saw the beautiful craft enter their harbour. The worst, however, of these iron boats is that two can play at shelling and long shots; and gunnery-practice is now brought to such perfection, that an iron steamer might very possibly soon get the worst of it from a heavy battery on the level of the sea; for a single accident to the machinery, protected as it is in that vessel, would, if there was no wind, put her entirely at the mercy of the gunners. The old wooden walls, after all, are better adapted to attack a fortress, as they can stand a good deal of hammering from both shot and shells. But to revert to matters more germane to the lakes. Volney, the first expounder of the system of the warm wind of the south supplying the great lakes, has received ample corroboration of his data from observation. The fact that the deflection of the great trade-wind from the west to a northern direction by the Mexican Andes Popocatepetl, Istaccihuetl, Naucampatepetl, &c., whose snowy summits have a frigid atmosphere of their own, is proved by daily experience.