NO. I AIR AND TUBERCULOSIS — HINSDALE 55 



checks the advent of fog- and where the early morning hours are as 

 bright and dry as the afternoons/ 



RADIATION FOGS 



Fogs are born of the sea and of the land. The sea fog is obviously 

 purer and less injurious than the smoke-laden fog of cities. There 

 are fogs and fogs ; " dry " fogs and " wet " fogs ; the fogs of the 

 coast and the fogs of mountain valleys and river courses ; but rarely 

 of the plains. Radiation fogs are different from sea fogs ; in dry 

 weather, on a cold still night when the lowest stratum of air is rap- 

 idly cooled by contact with the cold radiating earth, the watery vapor 

 is precipitated as minute globules. The colder the ground or the 

 deeper and colder the water on which fog rests, the more persist- 

 ent is the fog ; but as the sun warms the watery particles and over- 

 comes the heat lost by radiation, the fog lifts and floats upward. It 

 is bound to lift as its specific gravity diminishes. Slopes of hills, 

 especially their southern sides, some hundreds of feet above the low- 

 land or seashore, are thus comparatively free from these fogs and 

 are much drier and warmer than lower places in the neighborhood. 

 Such locations are far preferable to those of lower altitude. (Rus- 

 sell.) 



FOGS IN THE MOUNTAINS 



And here we see how local geographic conditions modify the 

 whole aspect of the question. On the North Atlantic Coast of the 

 United States there are no mountain ranges ; one cannot get away 

 from the fogs if he would ; while on the Pacific Coast, the mountains 

 and their foot hills are comparatively near and one can be in full 

 view of the seashore and yet be above the fog line. 



At Santa Barbara, one of the favorite California resorts for tuber- 

 culous patients, fogs occur frequently from May until October, but 

 are comparatively rare at other times. Dr. William H. Flint, who 

 practiced there for thirteen years, says that the fogs creep in from 

 the sea in the late afternoon, in the evening, or in the early morn- 

 ing, disappearing at an uncertain hour the following forenoon. Occa- 

 sionally fogs will persist all day and for a number of days consecu- 

 tively. In May and June, 1903, a foggy period continued for 

 seventeen days.* 



^ See A. G. McAdie : The Sun as a Fog Producer, Monthly Weather 

 Review, Washington, 1913 (778-779). 

 * Trans. Amer. Climat. Ass., 1904, P- 20. 



