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 54 DARCY. comparing mathematical theory and observation, he made a particular use of this principle in his “Memoir on Hy draulic Machines,” printed in 1754; and in this work he clearly shews how easy it is to make mistakes in looking by experiment for the laws of such effects as are suscep tible of a maximum or minimum; and indicates at the same time, how a system of experiments may be formed which shall lead to a discovery of these laws. All Darcy's works bear the character which results from the union of genius and philosophy; but as he measured every thing upon the largest scale, and required infinite accuracy in experiment, neither his time, fortune, nor avocations, allowed him to execute more than a very small part of what he projected. He continued his experiments on gunpowder until the last moment of his life, but has left nothing behind him. He was amiable, spirited, and lively, and a great lover of independence; a passion to which he sacrificed even in the midst of literary society, when perhaps a little aristocracy may not be quite so dan gerous. Darcy, though estranged from his native country by circumstances, yet possessed a true Irish heart, as he not only loved and respected i t , but became the friend and protector o f every Irishman who visited Paris; nor could h e help feeling a secret pride, even i n the successes o f that enemy, against whom h e was s o often and s o honour ably t o himself, employed. Of his personal history, i t yet remains t o b e added, that i n the seven years' war h e served i n the regiment o f Fitz-James; i n 1770, h e was appointed mareshal d e camp; and the same year the Aca demy o f Sciences admitted him t o the rank o f pensionary. I n 1777, h e entered into the matrimonial state with a niece who was brought u p under his care a t Paris, and then took the name o f Count Darcy. Death terminated his useful existence i n two years after this marriage, dying of a cholera morbus, on the 18th o f October, 1779. Con dorcet wrote his “Eloge,” published i n the History o f the Academy, and seems throughout anxious t o d o justice