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
employees. 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
at the Philadelphia Centenial Exhibition in 1876, where it astonished
Sir William Thomson.

In 1876, Edison sold his factory at Newark, and retired to Menlo Park, a
sequestered spot near Metuchin, on the Pennsylvania Railroad, and about
twenty-four miles from New York. Here on some rising ground he built a
wooden tenement, two stories high, and furnished it as a workshop and
laboratory. His own residence and the cottages of his servants completed
the little colony.

The basement of the main building was occupied by his office, a choice
library, a cabinet replete with instruments of precision, and a large
airy workshop, provided with lathes and steam power, wher