Telegraph relays 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, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
This relay includes a marble base and was made by Charles T. Chester of New York City. The electromagnet coils are fixed but the steel core can be moved to adjust the strength of the magnetic field.
Alexander Graham Bell demonstrated several experimental telephones at the Philadelphia Centennial Exposition in 1876. This unit features a single electro-magnet and could be used both as transmitter and receiver. Bell approached the problem of transmitting speech differently from other telephone inventors like Elisha Gray and Thomas Edison. They were mostly experienced telegraphers trying to make a better telegraph. Bell's study of hearing and speech more strongly influenced his work.
Model to accompany US patent number 132, "Electric Motor, issued to Thomas Davenport, 25 February 1837. This is the first US patent issued for an electric motor. No extant markings. The patent claims: "Applying magnetic and electromagnetic power as a moving principle for machinery in the manner above described, or in any other substantially the same in principle". Wooden base, 9 by 14 in., supported on four curved legs, carrying a circular frame, in which there are four rough electro-magnets, painted red, made to revolve within a ring of steel magnets. The steel magnets in the ring are crescent-shaped can be lifted out of the frame. Reference: W. James King, Development of Electrical Technology in the 19th Century (Smithsonian Institution, 1962), 264.
This model was made by Vermont blacksmith Thomas Davenport (1802-1851) as a replacement for his original patent model. The original was destroyed in the 1836 fire at the US Patent Office. Davenport may have incorporated improvements in this model that are not reflected in the patent drawings.
Alfred Vail made this key, believed to be from the first Baltimore-Washington telegraph line, as an improvement on Samuel Morse's original transmitter. Vail helped Morse develop a practical system for sending and receiving coded electrical signals over a wire, which was successfully demonstrated in 1844.
Morse's telegraph marked the arrival of instant long-distance communication in America. The revolutionary technology excited the public imagination, inspiring predictions that the telegraph would bring about economic prosperity, national unity, and even world peace.