Edison had now entered definitely upon that career as an inventor which has left so deep an imprint on the records of the United States Patent Office, where from his first patent in 1869 up to the summer of 1910 no fewer than 1328 separate patents have been applied for in his name, averaging thirty-two every year, and one about every eleven days; with a substantially corresponding number issued. The height of this inventive activity was attained about 1882, in which year no fewer than 141 pat- ents were applied for, and seventy-five granted to him, or nearly nine times as many as in 1876, when invention as a profession may be said to have been adopted by this prolific genius. It will be understood, of course, that even these figures do not represent the full measure of actual invention, as in every process and at every step there were many discoveries that were not brought to patent registration, but remained "trade secrets." And furthermore, that in practically every case the actual patented invention followed from one to a dozen or more gradually developing forms of the same idea.