Fortunately, he can work without stimulants, and, when the strain is
over, rest without narcotics; otherwise his exhausted constitution,
sound as it is, would probably break down. Still, he appears to be
ageing 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
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.
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