to form the
dash, reached the wheels, one of them dropped into a lower hole. Before
it could get out, the other wheel dropped into the hole at the apex of
the triangle, thus continuing the connection, which was still further
prolonged by the first wheel dropping into the third hole. Thus, an
extended contact was made, which, by transmitting a long impulse,
resulted in the marking of a dash upon the receiving tape.

This method was in successful commercial use for some time in the early
seventies, giving a speed of from three to four thousand words a minute
over a single line, but later on was superseded by Edison's Roman letter
system, above referred to.

The subject of automatic telegraphy received a vast amount of attention
from inventors at the time it was in vogue. None was more earnest
or indefatigable than Edison, who, during the progress of his
investigations, took out thirty-eight patents on various inventions
relating thereto, some of them covering chemical solutions for the
receiving paper. This of itself was a subject of much importance and
a vast amount of research and labor was expended upon it. In the
laboratory note-books there are recorded thousands of experiments
showing that Edison's investigations not only included an enormous
number of chemical salts and compounds, but also an exhaustive variety
of plants, flowers, roots, herbs, and barks.

It seems inexplicable at first view that a system of telegraphy
sufficiently rapid and economical to be practically available for
important business correspondence should have fallen into disuse. This,
however, is made clear--so far as concerns Edison's invention at any
rate--in Chapter VIII of the preceding narrative.

IV. WIRELESS TELEGRAPHY

ALTHOUGH Mr. Edison has taken no active part in the development of
the more modern wireless telegraphy, and his name has not occurred in
connection therewith, the underlying phenomena had been noted by him
many years in advance of the art, as will presently be explained. The
authors believe that this explanation will reveal a status of Edison in
relation to the subject that has thus far been unknown to the public.

While the term "wireless telegraphy," as now applied to the modern
method of electrical communication between distant points without
intervening conductors, is self-explanatory, it was also applicable,
strictly speaking, to the previous art of telegraphing to and from
moving trains, and between po