Pressing the telegraph key closes the circuit and sends a short pulse (dot) electricity along the wire. Holding the key down a bit longer sends a longer pulse (dash). Originally, the incoming electrical pulses created a magnetic field, causing a pen to to move down to mark a dot or dash on a paper tape. As operators became more skilled, they found they could recognize the pattern of sounds for each letter and decode the message before the tape printed. By 1850, the pens were eliminated and the message transmitted by the sound of the clicks.

With a grant from Congress in 1843, Morse and his partners built a 40-mile telegraph line between Baltimore and Washington. By 1850, the United States had 12,000 miles of telegraph lines. The line was extended all the way to California in 1861 and on to Oregon in 1864. Messages which had taken ten days to reach California by Pony Express would now arrive the same day. And with the discovery of a waterproof coating, underwater telegraph cables made it possible to connect continents. The first working transatlantic cable was completed in 1866. By 1880, almost 100,000 miles of undersea cable carried messages around the world.

Businesses used the telegraph to check prices, place orders and confirm credit. The telegraph provided the communication necessary for firms to operate across the country and contributed to the rise of big businesses. Railroads used the telegraph to dispatch and monitor trains.  During the Civil War, both armies had telegraph crews to put up temporary lines to coordinate troop movements and report battle results. Newspaper reporters could witness important events and immediately report their stories for publication in the next day's paper. The competition to report news from many places led to the formation of the first wire service, Associated Press.

So many people sending telegraph messages meant bottlenecks at relay stations and delays in delivery. The potential profits from devising a way to make existing lines more efficient attracted inventors. Their efforts produced not only improvements to telegraphy but also new discoveries and entirely new inventions, such as the telephone.

Telegram

As the telegraph sounder clicked the dots and dashes of Morse code, the operator typed up the message on long strips of paper and pasted them on a blank form. A messenger would then deliver it to the recipient's home or business. Large companies that sent many telegrams would sometimes have their own telegraph operators.