In Edison's system of automatic telegraphy a paper tape was perforated with a series of round holes, so arranged and spaced as to represent Morse characters, forming the words of the message to be transmitted. This was done in a special machine of Edison's invention, called a perforator, consisting of a series of punches operated by a bank of keys--typewriter fashion. The paper tape passed over a cylinder, and was kept in regular motion so as to receive the perforations in proper sequence.

The perforated tape was then placed in the transmitting instrument, the essential parts of which were a metallic drum and a projecting arm carrying two small wheels, which, by means of a spring, were maintained in constant pressure on the drum. The wheels and drum were electrically connected in the line over which the message was to be sent. current being supplied by batteries in the ordinary manner.

When the transmitting instrument was in operation, the perforated tape was passed over the drum in continuous, progressive motion. Thus, the paper passed between the drum and the two small wheels, and, as dry paper is a non- conductor, current was prevented from passing until a perforation was reached. As the paper passed along, the wheels dropped into the perforations, making momentary contacts with the drum beneath and causing momentary impulses of current to be transmitted over the line in the same way that they would be produced by the manipulation of the telegraph key, but with much greater rapidity. The perforations being so arranged as to regulate the length of the contact, the result would be the transmission of long and short impulses corresponding with the dots and dashes of the Morse alphabet.