Nothing in this big establishment, often employing more than one hundred persons, is made for sale. It is wholly devoted to experimental work and tests. Its expenses, said to be more than $150,000 a year, are paid by the commercial companies in which Edison is interested, he, on his part, giving them the benefit of any improvements made. Thus in one room hundreds of incandescent electric lamps burn night and day the year through. Each lamp is specially marked and when it burns out more quickly than the average, or lasts longer, a special study is made as to the contributing causes. It may seem impossible that the suggestions of one man can keep busy a big workshop upon experiments the year round, but Edison says that the temptation is always to increase the force. When it is remembered that the list of Edison's patents reaches to seven hundred and forty, and that on the electric light alone he has worked out several hundred theories, the wonder ceases. Ten minutes' work with a pencil may sketch an apparatus that a dozen men cannot finish inside of a fortnight. When the new Orange laboratory was finished and Edison found himself with time and means at his disposal, his first thought was to take up his phonograph. The history of the great hopes built upon the phonograph and the bitter disappointment that followed is too familiar to need repetition here. As may be imagined, Edison is most keenly bent upon tightening the loose screw that has prevented it from doing all that its friends predicted for it. He still works at other problems, but chiefly as relaxation. He rests from inventing one thing by inventing something else. [Illustration: Library at Edison's Laboratory.]