Electrical Telegraph Sounder

Shown here on display is the Electrical Telegraph Sounder from around the 1870s to the 1880s. This device was used as a receiver (a receiver was a device used to receive any incoming morse code) on electrical telegraph lines during the 19th century. Invented by Alfred Vail after 1850 to replace the previous receiving device, the cumbersome Morse register (which involved recording the incoming Morse code on a paper tape), and the device was the first practical application of the electromagnet. Telegraph networks transmitted information by pulses of current of two different lengths, the "dots" and "dashes" of Morse code. A telegraph operator at the sending end of the line would create the message by tapping on a switch called a telegraph key, which rapidly connects and breaks the circuit to a battery (which the metal pin may have connected to), sending pulses of current down the line, creating a relay system.

Consisting of an electromagnet attached to the telegraph line, with an iron armature near the magnet's pole balanced on a pivot, held up by a counterweight. When current flowed through the electromagnet's winding, it created a magnetic field which attracted the armature, pulling it down to the electromagnet, resulting in a "click" sound. When the current ended, the counterweight pulled the armature back up to its resting position, resulting in a "clack" sound. Creating the beeping sound we associate with telegraphs today. Thus, as the telegraph key at the sending end makes and breaks the contact, the sounder echoes the up and down state of the key. As telegraph operators would be itinerant, moving from place to place as work arose, some models of the electrical telegraph sounder mount a key and a sounder on a single base (which this model we have on display may have possibly have, though the make and model is currently unknown).