an inaccurate value of the speed of light that had been supplied to him. He approached the National Physical Laboratory in Teddington in England and they agreed to do a new measurement of the speed of light. The new measurement vindicated Wadley's claim. In 1958 the Tellurometer was used to measure Manhattan (13.08 miles). The measurement took 1 hour (plus two hours for the technicians to move from the south end of the island to the north.) Previously the measurement had taken 5 days. When the system was demonstrated in England before a group including the British Prime Minister, Harold Macmillan, it showed that a line on the Salisbury Plain which had been used as the baseline for British surveying had been incorrectly calculated by 1.5 meters. Subsequent sales of the device earned more than R300 million (in 1960's terms) in foreign revenue for South Africa. Tellurometers are still manufactured in Plumstead, South Africa. Ionosonde At the CSIR he developed a local version of the device called an ionosonde for measuring the Earth's ionosphere; the original device was developed by Breit and Tuve in 1925. It is a specialised form of a radar detector used to measure the height of the ionised layers of air between 50 and 600 kilometers. This information gives insight into what is occurring during an ionospheric storm. The ionosonde was used to provide a transmission frequency prediction service to the SABC, the South African Postal Service (SAPO) and South African Military. Patents Distance measuring system. US3241139A (1964) Determining relative position by means of transit time of waves. US2907999A (1955) & US3229285A (1960) Device including a rotating magnet positioned relative to another magnet for indicating the presence of magnetizable elements. US3541438A (1967) Recognition DSc in electrical engineering - thesis "Heterodyne Techniques in Specialised Instrumentation". Honorary doctorate from the University of Cape Town. In 1967 he presented the electrical principles of the Tellurometer at the Royal Geographical Society. Gold medal from South African Institute of Electrical Engineers in 1960. Frank P. Brown Medal from the Franklin Institute in America in 1970 for Development of Microwave Surveying Instrument. The South African post office issued a 25-year commemorative stamp of Wadley and the Tellurometer in February 1979. Durban High School instituted an annual mathematics prize in his honour in 2016. Durban municipality named a street Trevor Wadley close in his honour. References General references Burton, Mike. "The Annotated Old