different kinds of Dry Fogs. 243 



III. Dry fogs at the horizon, of unknown origin. 



Horizon enfume, Fumee d 1 horizon ; Hale of the Swiss ; 

 Hozherauch of the Germans ; Callina of the Spanish. 



The dry fogs of which we have hitherto spoken are owing, 

 the one to the combustion of peat, the other to volcanic erup- 

 tions ; it is different with the smoke of the horizon. Scarcely 

 noticed by meteorologists, it has not hitherto been the subject 

 of proper examination. The notes found here and there are 

 insufficient to furnish a complete description, much less to 

 establish any theory. In endeavouring to trace the princi- 

 pal appearances of this phenomenon, I shall not attempt to 

 disguise either the difficulties or imperfections of this part 

 of my undertaking. If I draw the attention of observers to 

 it my object will be gained. 



The horizon-smoke appears to be more common and more 

 intense in the south than in the north of Europe, in warm 

 regions than in cold ones. Thus, in Spain, according to 

 Willkomm,it continues during the months of June, July, and 

 August, when the weather is fine. M. de Humboldt speaks 

 of it as a habitual appearance at Acapulco, on the western 

 side of Mexico, but not at Cumana, where this vapour, how- 

 ever, interfered with his astronomical observations from the 

 10th October to 3d November. In the north it is not seen 

 often ; we have not observed it in Lapland. In Switzerland 

 it appears more common, and strikes the attention of every 

 one, because it conceals the view of the chain of the Alps 

 during the fine weather which attends the north and north- 

 east winds. In every instance it appears in connection with 

 a clear sky, and, in general, north winds. 



Its appearance is that of a gray or reddish smoke sur- 

 rounding the horizon, and rising at the maximum to 20 or 25 

 degrees above it. Commonly its thickness is only from 5 

 to 10 degrees. The upper edge is not distinctly defined on 

 the sky ; the latter has not the deep azure colour observed 

 before rain, and is of a bluish white. The air is not per- 

 fectly transparent, objects are indistinct and do not appear 

 near the spectator as in days when the air is saturated with 

 moisture. Travellers who then ascend mountains, induced 



