ASTRONOMY: C. G. ABBOT 
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perate zone stations show opposition of variation. Polar stations show 
direction variation. If these results shall be confirmed and enlarged they bid 
fair to aid in actual weather forecasting, for the changes are by no means 
small. 
In view of the scientific and utilitarian interest associated with the vari- 
ability of the sun, I have long desired that several cloudless observing stations 
might take up 'solar constant' work. In 1914 I made a trip to Australia 
expecting that the Australian Government would take it up. This hope was 
frustrated by the war. 
In 1916 Secretary Walcott appropriated from the income of the Hodgkins 
Fund to equip and maintain for several years such a station in South America, 
but owing to the war it was temporarily located in the North Carolina moun- 
tains in 1917. The station proved very cloudy, and now it has proved pos- 
sible though very expensive to go to Chile. 
After correspondence with the South African, Indian, Argentine and 
Chilean meteorological services I became convinced that near the nitrate 
desert of Chile is to be found the most cloudless region of the earth easily 
available. Dr. Walter Knoche of Santiago has most kindly furnished two 
years (1913 and 1914) of unpublished daily meteorological records for a 
number of Chilean stations. In his judgment and mine the best is Calama 
on the Loa River, Lat. S. 22° 28', Long. W. 68° 56', Altitude 2250 meters. 
For the two years the average number of wholly cloudless days is at 7 a.m. 
228; 2 p.m., 206; 9 p.m., 299; and of wholly cloudy days, none. The precipi- 
tation is zero; wind seldom exceeds 3 on a scale of 12; temperature seldom 
falls below 0° or above 25°C. 
Our expedition, Director Alfred F. Moore, Assistant Leonard H. Abbot, 
reached Calama June 25, 1918, equipped with a full spectro-bolometric, pyr- 
heliometric, and meteorological outfit of apparatus, as well as with books, 
tools, household supplies, and everything which we could furnish to make the 
work successful and life bearable. We are under great obligations to the 
Chilean Government for facilitating the expedition in many ways, and to the 
Chile Exploration Company who have given the expedition quarters and 
observing station at an abandoned mine near Calama. Many others in 
Antofagasta, Chuquicamata and Calama have been of great assistance. 
The apparatus is set up in an adobe building about 30 feet square, in which 
the observers also have sleeping apartments. A 15-inch two-mirror coelostat 
reflects the solar beam to the slit of the spectro-bolometer. We use a Jena 
ultra-violet crown glass prism and speculum metal mirrors in the spectro- 
scope. The linear bolometer is in vacuum, and constructed in accord with 
complete theory for greatest efficiency. Its indications as measured by a 
highly sensitive galvanometer are recorded photographically on a moving 
plate which travels proportionally to the movement of the spectrum over the 
bolometer. Successive bolometric energy spectrum curves each occupying 
8 minutes of time are taken from early morning till the sun is high and are 
