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It was in the late 1800’s when Dr. Samuel
Peirpont Langley proposed that the sun caused
 changes in the climate of the earth. He believed
 that by measuring these, the solar constant, he
and other scientists could accurately predict the
weather. Dr. Charles G. Abbot, Dr. Langley’s protégé,
 began to pursue his theory, and began testing at the
Harquahala Mountain Observatory. Telescopes were
not used here. Instead they used a variety of
 instruments. A coelostat was used to first reflect
sunbeams into the observing chamber. Next, a theodolite
was used to measure the altitude of the sun above the
horizon. Then a pyranometer was used to measure the
heat from the atmosphere around the sun. Finally, two
pyrheliometers measured the heat from the direct and
scattered rays from the sun. Readings of these
instruments, were recorded onto other instruments. Then, scientists calculated the data by hand, and sent the reports to the Smithsonian Institution of Washington D.C. This data was compared with recordings from other observatories from around the world. Eight scientists from 1920-1925 were sent from the Smithsonian Astrophysical Observatory were sent from Washington D.C. However, in 1925, it was decided that the severe weather, increased haziness in the air, and difficult access caused the station to be moved to Table Mountain in southern California.