﻿NO. 



SMITHSONIAN EXPLORATIONS, I922 



29 



The cost of these various improvements, which have made living on 

 the mountain very much more comfortable, has been borne by funds 

 provided for the purpose by Mr. John A. Roebling, of New Jersey, 

 to whom the Institution is greatly indebted for his generous interest 

 in its solar radiation program. 



A notable case of fluctuation in the solar radiation has recently 

 been reported from the Arizona station. A fall of 5 per cent in 

 the solar heat occurred, beginning about the 15th of October and 



Fig. t,2>. — Mount Harqua Hala and garage at foot, Ar 



izona. 



reaching its minimum on the 21st, and then quickly recovering to 

 the normal by the 25th. By inquiry at the U. S. Naval Observatory, 

 it is learned that a very notable new group of sun spots was formed, 

 the first indications appearing about the 17th of October and the group 

 reaching great dimensions by the 21st when it neared the limb of the 

 sun and shortly disappeared over the edge, due to the solar rotation. 

 This occurrence is nearly parallel to that of March, 1920, when a 

 similar great drop in the solar heat occurred and a very extraordinary 

 sun-spot group passed over the sun. 



