An incomplete telegraph register with automatic speed regulator. At the side of the machine is a toothed wheel attached to one of the rollers in the drive train and engaging a worm gear at the upper end of a revolving rod, to the lower end of which are attachments which formerly had two adjustable fans. The fans were made to open and close automatically and control the speed of the machine. William Clark of Philadelphia made this register as a test of his speed regulation design.
Telegraph registers are electrically-activated printers that receive Morse code messages. The message travels as a series of electrical pulses through a wire. The pulses energize the register’s electromagnets which move a lever-arm holding a pen or stylus. A clockwork mechanism pulls a strip of paper across the pen or stylus, recording the message. Short pulses draw or emboss a dot, slightly longer pulses a dash. The sequence of dots and dashes represent letters and numbers.