fact that, on account of the rapid succession of the electric
impulses, there was not sufficient time between them for the electric
action to cease entirely. Consequently the line could not clear itself,
and became surcharged, as it were; the effect being an attenuated
prolongation of each impulse as manifested in a weaker continuation of
the mark on the tape, thus making the whole message indistinct. These
secondary marks were called "tailings."

For many years electricians had tried in vain to overcome this
difficulty. Edison devoted a great deal of thought and energy to the
question, in the course of which he experimented through one hundred
and twenty consecutive nights, in the year 1873, on the line between
New York and Washington. His solution of the problem was simple but
effectual. It involved the principle of inductive compensation. In
a shunt circuit with the receiving instrument he introduced
electromagnets. The pulsations of current passed through the helices of
these magnets, producing an augmented marking effect upon the receiving
tape, but upon the breaking of the current, the magnet, in discharging
itself of the induced magnetism, would set up momentarily a
counter-current of opposite polarity. This neutralized the "tailing"
effect by clearing the line between pulsations, thus allowing the
telegraphic characters to be clearly and distinctly outlined upon the
tape. Further elaboration of this method was made later by the addition
of rheostats, condensers, and local opposition batteries on long lines.

The other difficulty above referred to was one that had also occupied
considerable thought and attention of many workers in the field, and
related to the perforating of the dash in the transmission tape. It
involved mechanical complications that seemed to be insurmountable, and
up to the time Edison invented his perforating machine no really good
method was available. He abandoned the attempt to cut dashes as such, in
the paper tape, but instead punched three round holes so arranged as
to form a triangle. A concrete example is presented in the illustration
below, which shows a piece of tape with perforations representing the
word "same."

The philosophy of this will be at once perceived when it is remembered
that the two little wheels running upon the drum of the transmitting
instrument were situated side by side, corresponding in distance to the
two rows of holes. When a triangle of three holes, intended