NO. 3 SMITHSONIAN E.\l'l,ORATIONS, I915 II7 



FOG CLEARING INVESTIGATIONS 



With the aid of a grant from the Smithsonian Institution, a com- 

 mittee of electrical engineering experts tinder the general direction 

 of Mr. F. G. Cottrell continued during 191 5 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 

 efifect, whereas in treating fog, it is 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 difificulties 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 exj)erience 

 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, 19 15, 

 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. 



