On June 21, 1880, Bell's assistant transmitted a wireless voice telephone message a considerable distance, from the roof of the Franklin School in Washington, D.C., to Bell at the window of his laboratory, some 213 metres (700 ft) away, 19 years before the first voice radio transmissions.
On June 21 , 1880 , Bell 's assistant transmitted a wireless voice telephone message a considerable distance , from the roof of the Franklin School in Washington , D.C. , to Bell at the window of his laboratory , some 213 metres ( 700 ft ) away , 19 years before the first voice radio transmissions .
Bell and his assistant first used their photophone on what date?
Bell and his assistant first used their photophone on what date ?
June 21, 1880
June 21, 1880