.

After trying several experiments on surfaces of various shapes, he ascertained the difference of resistance in different cases, suggested the probable cause of these variations, and opened a large field for future curious and useful speculation; useful it may be called, as well as curious, because such knowledge applies immediately to the wants and active business of life, to the construction of wind- and water-mills, and to the extensive purposes of navigation.

The theory of philosophers and the practice of mechanics and seamen were, and perhaps are still, at variance as to the manner in which sails of wind-mills and of ships should be set.

Dr.Hooke, in his day, expressed "his surprise at the obstinacy of seamen in continuing, after what appeared the clearest demonstration to the contrary, to prefer what are called bellying or bunting sails, to such as are hauled tight." The doctor said that he would, at some future time, add the test of experiment to mathematical investigation in support of his theory.
'It is remarkable that this test of experiment, when at length it was applied, confirmed the truth of what the philosopher had reprobated as an obstinate vulgar error.

My father, in his Essay on the Resistance of the Air, gives the result of his experiments on a flat and curved surface of the same dimensions, and explains the cause of the error into which Dr.Hooke, M.Parent, and other mathematicians had fallen in their theoretic reasonings.