Milliken-type telegraph repeater

Telegraph repeaters amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, limiting the distance a message could travel. Repeaters remedied that problem by detecting a weak signal and using a local power source to re-energize and re-transmit the signal down the line.

This Milliken-repeater was used on the New York, Pennsylvania & Ohio Railroad in the 1880s or '90s. George F. Milliken, manager of the Boston office of Western Union, introduced a new type of automatic telegraph repeater in 1864 designed to remedy a defect in prior models. Sometimes a delay in energizing one electromagnet in a repeater resulted in a lever being held by another electromagnet too tightly for the springs to release. An operator had to send a dot at just the right time to activate the repeater. Milliken used an auxiliary magnet and added a mechanical linkage to solve the problem. Franklin Pope wrote in 1868, “One of the principal advantages in the construction of Milliken's repeater consists in the fact that any slight variation in the strength of the extra local circuit, from weakness of the battery or other causes, does not affect the adjustment of the relay magnets.... The adjustment and action of the two magnets are entirely independent of each other, .... The relay levers also move more freely, being unencumbered with extra armatures or other appliances.” Charles Davis and Frank Rae wrote almost ten years later that Milliken’s repeater, “is more simple in principle and much easier adjusted.” Western Union adopted the distinctive looking “Milliken repeater” as a standard piece of equipment and the term became generic.

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