We have received a letter from Joseph E. Holmes, superintendent of machinery at the Crystal Palace, wherein Mr. Ellett's views respecting his proposed mode of improving the navigation of the Ohio River, and our own opinions respecting them, as expressed on page 309, Vol. 8, Scientific American, are dissented from. He believes, as he is acquainted with the grounds on the head waters of the Ohio' the plan is impracticable but not impossible. 1 It is not," he says," what is possible should be done, but what is politic." Of the policy spoken ot, the people in that section of the country are the most interested, and no doubt the best judges. If any great work—no matter what its magnitude may be—can be demonstrated to produce beneficial and economical results, we like to advocate the measure, and the greater the work the more highly do we desire to see it executed. We like to hold up the accomplishment of great works to our people. If Mr. Ellett's data can be trusted, then the work can be done, and done to produce good results. We cannot contradict his data, and the only way to show the impracticability, is to point out the incorrectness of his calculations, statistics, & c.