﻿26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



than they would at a cloudy, humid, hazy region where the air is con- 

 taminated, perhaps by the smoke of a great city. 



The consequence is that air expansion, due to the increased tempera- 

 ture accompanying increase of solar radiation, takes place in much 

 larger proportion in the humid, hazy regions than it does in the 

 cloudless, clear ones, and so the air must flow from the regions of the 

 former condition to those of the latter. This produces changes in 

 barometric pressures which in turn produce the winds and cyclonic 

 movements which are so familiar. With the changes of season and 

 other variable conditions, the regions which are sources of these 

 cyclonic disturbances move about from place to place. This alters the 

 direction of the winds, and, as is w^ell known, the temperature depends 

 intimately on the prevailing winds at every locality. This may explain 

 why it is that we are not to expect at every station and at every time 

 of the year colder weather when the solar radiation is lower. We 

 may have exactly the reverse, depending on these secondary effects. 

 Consequently the study of the dependence of weather on solar radia- 

 tion must be very long continued and thorough before it will be 

 possible to hazard predictions based upon the variation of the sun, or 

 even to know for certain that the variations of the sun are of import- 

 ance for our forecasters. The Smithsonian Institution, however, hav- 

 ing developed the methods of measurement of the solar heat, seems 

 in duty bound to continue these careful determinations of it long 

 enough to furnish a first rate groundwork of data from which 

 meteorologists can determine these interesting relations. 



Notable improvements have been made at both stations through the 

 enthusiastic work of the directors, INIr. L. B. Aldrich at Montezuma 

 and Mr. A. F. IMoore at Harqua Hala. One of the most striking 

 of these is the introduction at Montezuma of a windmill, situated at 

 the very top of the mountain, and furnishing sufificient power to 

 produce electric lights and to charge the storage batteries used al^out 

 the dwelling-house and the observing station. Some additions have 

 been made to the living quarters at each station in order to add to the 

 comfort of the observers and their families. The accompanying illus- 

 trations show the Montezuma station whh the windmill as now 

 installed. Readers may compare these with previous illustrations of 

 former Exploration Pamphlets. 



An expedition was made by Dr. Abbot to the station on Mt. Wilson, 

 formerly occupied for the measurements of the solar heat, but now 

 reserved for occasional occupation for the study of problems requiring 

 good, cloudless observing conditions not found in Washington. Three 



