The field of electronics deals with the practical application and manipulation of electricity and electromagnetic phenomena. The invention of the vacuum tube in the early 20th century marked the beginning of modern electronics. The vacuum tube was capable of amplifying weak radio signals, allowing them to be transmitted over greater distances. Vacuum tubes also allowed music and voice to be superimposed onto radio waves for transmission. The early study of electronics revolutionized a number of fields, especially the field of communications. Because of the vacuum tube, the technology of radio communications was highly developed by World War II. After the war, electronics research continued to advance rapidly. Post-war advances include the earliest examples of digital computers and, eventually, transistors and integrated circuits: miniaturized replacements for the vacuum tube.