372 WRITINGS OF JOSEPH HENRY. [1874 



rent being warmer than the ocean through which it passes, 

 tends to produce dense fogs in the region of the Aleutian 

 Islands and the coast of Alaska. As this current descends 

 along the American coast into lower latitudes it gradually 

 loses its warmth, and soon assumes the character — in regard 

 to the water through which it passes, of a comparatively 

 colder stream; and to this cause we would attribute the 

 prevalence of fogs on the coast of Oregon and California, 

 which are most prevalent during the spring and early sum- 

 mer, with wind from the north-west and west. 



From what has been said, it is evident that the fogs in the 

 Aleutian Islands occur chiefly in summer, when south-west- 

 erly winds prevail and mingle the moist air from the warm 

 current with the colder air of the more northerly latitude. 

 In winter, the wind being from the north chiefly, the moist 

 air is driven in an opposite direction, and dense fogs there- 

 fore at this season do not prevail. 



In regard to the fogs on the coast of Maine, the following 

 interesting facts were furnished me by the late Dr. William 

 Stimpson, formerly of the Smithsonian Institution, and of 

 the Chicago Academy of Sciences, who had much experience 

 as to the weather during his dredging for marine specimens 

 of natural history in the region of Grand Manan Island, at 

 the entrance of the Bay of Fundy. 



"So sharply marked," says Dr. Stimpson, "is the difference 

 of temperature of the warm water from the Gulf-stream and 

 that of the polar current, that in sailing in some cases only 

 a few lengths of a ship the temperature of the water will 

 change from 70° to. 50°. The fog frequently comes rolling 

 in with the speed of a race-horse; in some cases while dredg- 

 ing, happening to turn my eyes to the south, a bank of fog 

 has been seen approaching with such rapidity that there 

 was scarcely time in which to take compass-bearing of some 

 object on shore by which to steer, before I would be entirely 

 shut in, perhaps for days together." He also mentions the 

 fact that it frequently happened during a warm day, while 

 a dense fog existed some distance from the shore, close in to 

 the latter there would be a space entirely clear; this was 



