Although the idea of transmitting messages via electrical signals dated back to the eighteenth century, it was not until the 1820s that advances in the study of electricity and magnetism made that a practical reality. In 1837, William Fothergill Cooke and Charles Wheatstone invented a telegraphic system that used electrical currents to deflect magnetic needles, thus transmitting coded messages. This design soon made its way all across Britain, appearing in every town and post office. By the mid-1800s, a telegraphic cable was laid across the English Channel, the Irish Sea, and the North Sea. In 1866, the SS "Great Eastern" successfully laid the transatlantic telegraphic cable. A global network boomed towards the end of the century.