William H. Hoover, American astrophysicist and meteorologist, was temporarily engaged as an assistant at the Astrophysical Observatory of the Smithsonian Institution, Washington, by its director, Dr Charles G. Abbot*, in March 1923. He was trained to become the director of a proposed solar radiation station in Argentina and constructed a bolometer and a galvanometer to be used there. In 1926 he was appointed as field director of the newly erected solar radiation station on Brukkaros Mountain, some 100 km north of Keetmanshoop in South West Africa (now Namibia). He was to be assisted in this position by Mr Frederick A. Greeley and it was understood that they would occupy the station for three years. They left the United States in August 1926 and arrived in Cape Town on 13 September. Hoover, who was a widower at this time, was accompanied by his future wife, Miss Johnson, and their infant daughter. They travelled by rail to Keetmanshoop and had the instruments and household goods transported to the mountain by ox-waggon. Miss Johnson and her daughter stayed in Keetmanshoop until she married Hoover in December, when they too moved to the mountain.
The solar radiation stations of the Astrophysical Observatory were erected to study possible variations in the solar constant - the rate at which energy reaches the earth (outside its atmosphere) from the sun [about 1.388 kW/m2]. Measurements of solar radiation made on the earth's surface therefore had to be corrected for atmospheric absorption. The instruments used included an Abbot silver-disk pyrheliometer to measure the total flux of solar radiation reaching the ground, a pyrometer to measure radiation from a circular region of sky around the sun (excluding the sun itself), and a bolometer to measure the amount of radiation received at different wavelengths in the visible and infrared spectrum. After some preliminary observations during November 1926 daily measurements started on 9 December. The observations usually occupied the whole morning from soon after sunrise. The rest of the day was spent in computing the results, which took several hours. Results were regularly reported to Dr Abbot in Washington, who compared them to those of the other solar stations and interpreted and published the findings [See Abbot, C.G.].
In January 1927 Hoover offered to start meteorological observations at Brukkaros and supply them to the Weather Bureau in Windhoek. The offer was accepted and meteorological instruments were received at the solar station in July. Daily readings started on 11 August 1927 and were continued until the station closed towards the end of 1931.
Hoover's wife collected plants on the mountain, especially after good rains fell early in 1929. and after her return to America donated her collection of 103 specimens to the United States National Museum in Washington. She also wrote a popular account of life on the mountain, "Keeping house for the Shepherds of the sun", for National Geographic Magazine (1930), using the author name "Mrs Willliam H. Hoover".
Hoover and his party left Brukkaros on 5 September 1929, at the end of their three year term, and returned to Washington. They were replaced by Mr Louis O. Sordahl* (director) and Mr A.G. Froiland (assistant). Hoover was next appointed as associate research assistant in the Division of Radiation and Organisms of the Smithsonian Institution and was promoted to senior astrophysicist in 1937. He held this post until his unexpected death in 1953. His publications included "Carbon dioxide assimilation in a higher plant" (Smithsonian Miscellaneous Collections, 1933), "The dependence of carbon dioxide assimilation in a higher plant on the wave length of radiation" (Ibid, 1937), "A sensitive radiometer" (Ibid, 1945, with C.G. Abbot and L.B. Clark), and "Silver-disk pyroheliometry" (Ibid, 1953). During 1935 he visited the solar radiation stations in Chile and Egypt to install improved pyroheliometers.
