Most vacuum tubes consisted of an array of metal wires and plates sealed inside a glass tube, with metal prongs coming out the bottom for plugging into the electrical equipment. Before the tube was sealed, all of the air w.as sucked out, to form a vacuum inside the tube around the metal parts. A typical vacuum tube was around 1 inch in diameter and 2 to 3 inches long, resembling a minia. ture space ship. By 1910, vacuum tube technology had made the radio practical but still not for the general public. These early radios were used primarily for communication between oceangoing ships and to the shore. Such communication became especially important