ssage when received
would not require translation and rewriting, but would automatically
appear on the tape in plain letters and words, ready for instant
delivery.

The result was his automatic Roman letter system, the basis for which
included the above-named general principles of perforated transmission
tape and electrochemical decomposition. Instead of punching Morse
characters in the transmission tape however, it was perforated with
a series of small round holes forming Roman letters. The verticals
of these letters were originally five holes high. The transmitting
instrument had five small wheels or rollers, instead of two, for making
contacts through the perforations and causing short electric impulses
to pass over the lines. At first five lines were used to carry these
impulses to the receiving instrument, where there were five iron pins
impinging on the drum. By means of these pins the chemically prepared
tape was marked with dots corresponding to the impulses as received,
leaving upon it a legible record of the letters and words transmitted.

For purposes of economy in investment and maintenance, Edison devised
subsequently a plan by which the number of conducting lines was reduced
to two, instead of five. The verticals of the letters were perforated
only four holes high, and the four rollers were arranged in pairs, one
pair being slightly in advance of the other. There were, of course,
only four pins at the receiving instrument. Two were of iron and two of
tellurium, it being the gist of Edison's plan to effect the marking
of the chemical paper by one metal with a positive current, and by the
other metal with a negative current. In the following diagram, which
shows the theory of this arrangement, it will be seen that both the
transmitting rollers and the receiving pins are arranged in pairs,
one pair in each case being slightly in advance of the other. Of these
receiving pins, one pair--1 and 3--are of iron, and the other pair--2
and 4--of tellurium. Pins 1-2 and 3-4 are electrically connected
together in other pairs, and then each of these pairs is connected with
one of the main lines that run respectively to the middle of two groups
of batteries at the transmitting end. The terminals of these groups of
batteries are connected respectively to the four rollers which impinge
upon the transmitting drum, the negatives being connected to 5 and 7,
and the positives to 6 and 8, as denoted by the letters N and P. The