Mississirn RIVER.—A very beautiful and comprehensive volume has lately been issued from the press ot Messrs. Lippincott & Grambo, Phila., by Charles Ellet, Jr., C. E., a name not a little famous in the history of American engineering. It treats of improving the navigation of the Ohio and Mississippi Rivers, and of plans for protecting the Mississippi Valley from inundation. He has adopted the mouth of the Ohio Riveras the head of the Delta of the Mississippi, and from this point to the Gulf of Mexico the waters of the river flow on to the sea for five hundred miles in a direct line with a fall of 8 inches to the mile ; but because of windings the waters traverse a space of 1,178 miles, and command a great extent of country. The lands on its banks are very fertile, and it is calculated that 40,000 square miles of them are lower than high water during the floods, and are therefore frequently inundated in spite of artificial embankments, to the great destruction of planters' property. To obviate the disasters of waters breaking through the artificial banks or levees, Mr. Ellet entered into investigations, the results of which he has presented in this work, which certainly does great credit to his ability and energy. It is computed that there are no less than 16,000,000 acres annually overflowed by the waters of the Mississippi, and if this could be prevented, all that amount of land might soon be converted ! into exceedingly productive cotton and sugar plantations. The Mississippi flows along between banks nearly a mile wide, and about 100 feet deep. Experiments made by Mr. Ellet to test the velocity of the river did not harmonize in their results with the rules laid down by Du Buat and De Prony for deducing approximately the velocity of all currents beneath the surface. The average velocity of the Mississippi was found to be five miles per hour, and sometimes 7 miles per hour at high water, but did not discharge as much water below New Orleans, as at one mile below the mouth of the Ohio in a flood—the discharge per second at the latter place being 1,223,000 cubic feet, and at the former place only 995,-000 cubic feet, 228,000 less, which was lost in overflowing the banks. To remedy the evils of overflowing the lands behind the levees of the Mississippi, Mr. Ellet proposes artificial outlets for the surplus water below the Red River and other places, and thus carry the surplus waters into the sea; also the making of stronger embankments or levees ; and what is more original, the making ot great reservoirs or artificial lakes in the hill countries of the Mississippi to hold back a portion of the surplus water. The plan of artificial lakes for this purpose is certainly a bold and original proposition. We are convinced that much evil by crevasses would be obviated if more care was exercised in building up the levees or banks erected on the Mississipi. In the flood of 1849, it is calculated that five or six millions of dollars worth of the cotton crop was destroyed on the Red River alone. OHIO RIVER.—This noble tributary of the Mississippi, rises on the borders of Lake Erie, at an elevation of 13,000 feet above the level of the sea, and nearly 700 above the level of the lake. A boat may start with sufficient water within seven miles of Lake Erie, and float down uninterruptedly to the Gulf of Mexico, a distance of 2,400 miles. The length of the Ohio is stated by Mr. Ellet to be 975 miles. The unequal distribution of its volume of water in different seasons of the year is the only efficient obstruction to the complete and absolute superiority of the Ohio river, as a channel of commerce, overall others in the world, either natural or artificial. The Nile, the Ganges, the Danube, and even the Missouri, the Mississippi, and the Amazon, have in other respects greater obstacles to their uniform navigation than has the Ohio. But it must be admitted that in a large part of the year the Ohio is reduced so low that its numerous sand shoals nearly destroy its navigation. The great object of Mr. Ellet is to improve the navigation of the Ohio by equalizing its depth of water. This he proposes to do by constructing artificial reservoirs or lakes to collect the surplus water during floods, so as to prevent inundations, and then to use the waters so saved to be let out in the dry periods of summer, so as to give the Ohio river a continual depth ot about 6 feet. At the present moment there is sometimes only a depth of 2 feet of water on the bar at Wheeling,and at other times no less than 30 feet. We hope to see the plans of Mr. Ellet carried out ; we believe them to be not only feasible, but eminently ingenious and practical, and if carried out will be the means of benefitting all the countries watered by the tributaries of the Mississippi, and that noble river itself, to an amount tar beyond our ability to compute at present.