Secretary Charles G. Abbot Reading the Pyrheliometer, c. 1940, Smithsonian Archives - History Div, In the South Yard behind the Smithsonian Institution Building , the Fifth Secretary (1928-1944) of the Smithsonian Charles G. Abbot is taking a reading from a pyrheliometer. Charles G. Abbot was an astrophysicist and patented the pyrheliometer in 1941. A pyrheliometer is an instrument for measuring the sun's radiant energy that is received on the earth..