NO. 3 SMITHSONIAN EXPLORATIONS, IQI5 119 
The need is very urgent that other observing stations in remote 
regions of the earth take up the daily measurement of solar radiation 
in cooperation with the Astrophysical Observatory. Preferably not 
less than four stations in relatively cloudless regions, widely sep- 
arated, should be engaged in this work. The variation of the sun 
is established. Its influence on terrestrial climate and conditions 
of growth of vegetation cannot be well determined unless the results 
of the Astrophysical Observatory are verified and supplemented 
by prolonged routine observing at several cooperating stations. 
