NO. 3 SMITHSONIAN EXPLORATIONS, IQI5 II 
N 
FOG CLEARING INVESTIGATIONS 
With the aid of a grant from the Smithsonian Institution, a com- 
mittee of electrical engineering experts under the general direction 
of Mr. F. G. Cottrell continued during 1915 the investigations 
begun by the University of California in cooperation with the United 
States Lighthouse Service, relative to the clearing of fog by means 
of electrical precipitation. In a preliminary report read at the first 
meeting of the committee, Prof. Ryan of Stanford University, says, 
“ Science has established the fact that all dust and fog particles in 
the open atmosphere are electrified and subject to dispersion or 
precipitation. It is apparent, therefore, that a source of very high 
direct voltage with facilities for control and application may be of 
inestimable value in certain quarters and seasons for clearing fog 
away from a street, from along a passenger railway, from around 
the landing stages of a ferry, or possibly about or in advance of a ship 
under headway at sea.” 
The clearing of fog differs from the treatment of smoke and fumes 
in several respects, principally in that the smoke particles must plainly 
be actually deposited on the electrodes to bring about the desired 
effect, whereas in treating fog, it 1s only necessary to cause coales- 
cence of the minute particles into larger ones to give much greater 
transparency, even disregarding the more rapid settling of the larger 
drops. However, other difficulties are to be expected in the problem 
of clearing fog, such as the conditions arising from the continual 
immersion in the wet atmosphere. What is chiefly needed for an 
intelligent conception of the problem is actual first-hand experience 
in handling these and other unusual conditions. 
A great deal has been learned during the year about the electrical 
technique of the problem, and although days of suitable fog conditions 
have been extremely scarce, on the rare occasions of actual trial, 
very perceptible clearing for a short distance around the high tension 
wires was obtained as the fog swept past. 
STUDIES IN SOLAR RADIATION 
The Mount Wilson Station of the Astrophysical Observatory was 
occupied by Messrs. Abbot and Aldrich from May to October, 1915, 
and numerous measurements of solar radiation were made there. 
During June unusually many days were marred for these observa- 
tions by cirrus clouds, but the later months were uncommonly fine. 
In October almost every day proved suitable for the work. 
