Sir George Cayley, recently (Dec. 15) deceased in England, at the advanced age of 84 years, was a prominent inventor and a man of science. He invented a hot air engine, long before the Ericsson was dreamed of, and so enthusiastic was he in the belief that air was superior to steam as a motive agent, that he made experiments in the hope of perfecting his engine up to a period close upon his decease. Many eminent inventors and men of science, like Sir George, oftentimes get upon the wrong track, and go round and round in the same path, like the moon around the earth, and yet think they are going ahead&— always advancing&—because they keep the same face to the great center of attraction. He was a firm believer in the ultimate success of electricity as a motive agent in machinery, and he invented a very excellent instrument used in London for examinations of impure water3, such as those of the river Thames.