Maria adds:—­’Those ingenious ideas, which had been but the amusement of youth, as he advanced in life, he turned to public utility:  for instance, the mode of conveying secret and swift intelligence, which he had suggested at first only to decide a trifling wager between him and some young nobleman, he afterwards improved into a national telegraph, and through all difficulties and disappointments persevered till it was established.  In the same manner, his juvenile amusements with the sailing chariot led to experiments on the resistance of the air, which in more mature years he pursued in the patient spirit of philosophical investigation, and turned to good account for the real business of life, and for the advancement of science.

’On this subject, in the year 1783, he published in the Transactions of the Royal Society (vol. 73) “An Essay on the Resistance of the Air,” of which the object, as he states, is to determine the force of the wind upon surfaces of different size and figure, or upon the same surface, when placed in different directions, inclined at different angles, or curved in different arches. . . .  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. . . .

’It is remarkable that a man of naturally lively imagination and of inventive genius should not, in science, have ever followed any fanciful theory of his own, but that all he did should have been characterised by patient investigation and prudent experiment. . . .

’In science, it is not given to man to finish; to persevere, to advance a step or two, is all that can be accomplished, and all that will be expected by the real philosopher.