ASTRONOMY: C. G. ABBOT 
385 
This condition is well fulfilled. A change of 1% or less would suffice 
to bring almost every point on the line. Accordingly we may conclude 
that the spectro-bolometric determinations of the solar constant of radia- 
tion made at Mount Wilson and Calama mutually support one another 
and indicate a variability of the solar radiation. Since the two stations 
are situated in different hemispheres of the earth, separated by a dis- 
tance of upwards of 5000 miles, it must be conceded that the result 
strongly confirms our view of the short period variability of the sun. 
Investigations have already been made by Dr. Clayton and others 
on the correlation of terrestrial temperatures and pressures with these 
supposed changes in the sun, and affirmative results have been obtained 
by them to the question: Do the variations in the sun noticeably affect 
the terrestrial weather conditions? Dr. Clayton is so strongly convinced 
of the dependence between the weather and the solar radiation that at 
his desire the Argentine Government is obtaining daily telegraphic solar 
radiation reports from the station at Calama on which are based fore- 
casts of the temperature in Argentina. Hitherto the correspondence 
has been very good, so that Dr. Clayton is very sanguine that a great 
improvement in forecasting will result from these solar radiation ob- 
servations. The Brazilian Government has also, at his recommendation, 
begun comparisons. 
If the further studies of the correlations between terrestrial tempera- 
tures and solar variations yield similar affirmative results, it will proba- 
bly be necessary within a year or two to undertake the equipment of 
several additional solar radiation observing stations in the most cloudless 
regions of the earth. There should be not less than three additional solar 
radiation stations, and the cost of conducting them and the station at 
Calama would absorb an income of from thirty to forty thousand 
dollars per annum. It is to be hoped that funds for this purpose may 
become available to the Smithsonian Institution, for with the experience 
gained by the staff of the Institution it would be able to carry on the 
research in a way to obtain homogeneous and accurate results. 
The choice of sites for additional solar radiation stations involves 
investigation as to the most cloudless regions of the earth. None of the 
stations hitherto occupied, not even that at Calama, is as satisfactory 
as we could wish for. The most serious enemy to the research is the 
presence of cirrus clouds, or any other form of cloudiness, and it is a 
grave problem where in the world these are least numerous. The com- 
parison of the observations at the two stations in 1918 shows that no 
inconsiderable number of the days in which observations were made 
were unsuitable for the purpose on account of the changes of the atmos- 
