Page:Heroes of the telegraph (IA cu31924031222494).djvu/221

 before his time, and some of his assistants, not so well endowed with vitality, have, we believe, overtaxed their strength in trying to keep up with him.

At this period he devised his electric pen, an ingenious device for making copies of a document. It consists essentially of a needle, rapidly jogged up and down by means of an electro-magnet actuated by an intermittent current of electricity. The writing is traced with the needle, which perforates another sheet of paper underneath, thus forming a stencil-plate, which when placed on a clean paper, and evenly inked with a rolling brush, reproduces the original writing.

In 1873 Edison was married to Miss Mary Stillwell, of Newark, one of his employés. His eldest child, Mary Estelle, was playfully surnamed 'Dot,' and his second, Thomas Alva, jun., 'Dash,' after the signals of the Morse code. Mrs. Edison died several years ago.

While seeking to improve the method of duplex working introduced by Mr. Steams, Edison invented the quadruplex, by which four messages are simultaneously sent through one wire, two from each end. Brought out in association with Mr. Prescott, it was adopted by the Western Union Telegraph Company, and, later, by the British Post Office. The President of the Western Union reported that it had saved the Company 500,000 dollars a year in the construction of new lines. Edison also improved the Bain chemical telegraph, until it attained an incredible speed. Bain had left it capable of recording 200 words a minute; but Edison, by dint of searching a pile of books ordered from New York, Paris, and London, making copious notes, and trying innumerable experiments, while eating at his desk and sleeping in his chair, ultimately prepared a solution which enabled it to register over 1000 words a minute. It was exhibited