Edward Alfred Jennings, radio pioneer, started his career as an instrument maker in a British firm that manufactured telegraph equipment for railway companies. His skill in precision work resulted in his joining the firm of Robert Whitehead, which made the first modern naval torpedoes, where he was placed in the department specialising in firing mechanisms. Later he moved to the Government Instrument Factory at Holloway, near London. While there he applied for a post in the Post Office Establishment of the Cape Colony and was appointed as a mechanician (repair man), stationed in Cape Town, on 4 November 1893.
In 1896 Jennings was transferred to the Port Elizabeth telephone exchange (the oldest in the country, opened in 1882), where his job was to maintain and repair about 200 telephone instruments then in use. A common fault, resulting from infrequent use of the telephones, was that the carbon granules in the microphones became packed together, thus preventing the transmission of sound. In an attempt to fix this problem he experimented with replacing the microphone with a glass tube filled with silver filings, which he expected to be less likely to stick together. The experiment was not very successful, but he noted that whenever someone pressed the electric bell at the front door, his experimental receiver in the back of the house would produce a loud crackle. This compacted the silver filings (and so reduced their resistance - an effect discovered by D.E. Hughes more than a decade earlier and again demonstrated by Sir Oliver Lodge at Oxford in 1894), and required a gentle tap to loosen them again. In this way he accidentally, and apparently independently, discovered the principle of the "coherer", used by G. Marconi and others in the earliest types of wireless receivers. More intense responses in his receiver, including strong electric sparks, were caused by electric sparks produced some 140 m from his house by the recently introduced electric trams. He decided to request expert advice to explain the phenomenon and demonstrated the effect to four prominent persons, including George E. Cory*, then lecturer at St Andrew's College, Grahamstown, and R.H.H. Heenen*, resident engineer of the Port Elizabeth Harbour Board. No explanation was forthcoming.
Jennings continued to work on further improvements of his apparatus, guided by some newspaper reports of the experiments with wireless telegraphy conducted by G. Marconi in Italy (and from 1897 in England) and particularly the latter's first communication of an intelligible signal by radio waves in July 1896. Among others, assisted by his future wife, he built a Ruhmkorff coil (which contained more than 4 km of thin copper wire) to induce bigger sparks, and a condenser made up of 200 sheets of tinfoil. Subsequently, with the help of a colleague from the Telegraph Department, he sent a signal from his house in Sherlock Street to a primitive receiver in Cooper's Kloof, a distance of some 800 m, using wire netting as an aerial. In 1899 his experiments had progressed to such an extent that he achieve a record transmission distance of some 13 km, the transmitter being located in the Donkin lighthouse at Cape Recife. Communication with the lighthouse was established using a strip of wire netting as a transmitter aerial and a Morse tape machine printer.
On 8 May 1899 a paper by Jennings dealing with his experinents was read at a public meeting in the Port Elizabeth town hall. The paper, read by Alexander Marshall*, curator of the Port Elizabeth Museum, included a review of early attempts overseas to transmit information over a distance without the use of wires (by means of either induction, or electric currents flowing through the earth or water). In support of his own work Jennings demonstrated the transmission of a telegraph message by means of wireless telegraphy from one room in the building to another. In July 1899 a trial between Port Elizabeth and the mail steamer Cascon, lying in Algoa Bay some 5 km from shore, was carried out and proved successful.
At this time the success already achieved by Marconi and other investigators, with improved apparatus, was reported in the local press and Jennings appears to have terminated his experiments. Meanwhile wireless telegraphy was demonstrated also in Cape Town, on 11 February 1899 over a distance of some 120 m, by a group of prominent citizens including Dr J.C. Beattie* (professor of physics at the South African College), B. Baily (Metropolitan District Engineer to the Post Office) and H.D. Wilkinson (of the Eastern Telegraph Company). From this time wireless telegraphy rapidly came into use, also in South Africa, for communication with ships and lighthouses, using imported equipment.
Jennings stayed with the Post Office in Port Elizabeth, from 1910 as mechanician in charge of the workshop. In 1914 he was transferred to Johannesburg. Two years later, during World War 1 (1914-1918), he invented a device for the improvement of jets for producing carbide, but it appears not to have been put to practical use. In 1923 he retired from the Post Office and settled in Cape Town, where he remained until his death in 1951.