Ix PHOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



years advanced other views on the subject of these remarkable 

 winds, has recently published* a careful examination of the whole 

 question. 



He cites early writings of his own, beginning in the year 1837, 

 based on the principles of Hadley, and confii-med by the generaliza- 

 tions of Sir John Herschel, which show that the currents of heated 

 air, rising from the parched regions of Central Africa, must partake 

 of the more rapid velocity of the equatorial rotation, and, as they 

 pass northward, gain on the surface of the earth in the slower-mov- 

 ing higher latitudes, and gradually get deflected on their course to- 

 wards the poles, so as to assume the direction of south-westerly 

 winds. In winter, he holds that the chief heating area will lie far 

 to the south of the Sahara, and that the upper or return trade- 

 wind (ohere Passat) will turn off in such a direction, as not merely 

 to miss the Alps in its northerly course, but barely to touch the 

 southern corner of Greece. Its full force will thus sweep over Arabia 

 and Western Asia to the regions of the Caspian, the Aral, and Central 

 Asia. The hot winds which rise from the broiling African deserts may 

 therefore, where they begin to descend again towards the surface of 

 the earth, have been instrumental in promoting an unusual amount of 

 evaporation in Syria and the Aralo-Caspian plains, whilst the Fohn 

 would be derived from a more westerly origin, and probably from 

 the South Atlantic and West Indies. But the Swiss authors object 

 that the Fohn is a hot and very dry wind ; and Dove thereupon 

 quotes at length a series of observations and descriptions which 

 establish the fact that these storms, when they break upon the Alps, 

 are commonly, and in the winter especially, accompanied by heavy 

 rains, and in the higher districts by thick downfalls of snow. The 

 two instances more closely inquired into are the storms of the 6th 

 and 7th January, 1863, and 17th February, 1865, when the "wild 

 offspring of the desert," as the gale was termed by the Swiss papers, 

 raised the temperature considerably, and, including in its train 

 lightning, snow-storms, avalanches, and inundations, committed 

 fearful havoc. In the second case it was particularly observable 

 that, for some days before, the temperatui^e had been lower than 

 for forty years previously ; and whilst the result of a warm dry 

 wind impinging on this cold air would have been only to increase 

 its capacity for vapour, that of a warm moist wind, under the same 

 conditions, would be to condense the vapour, and to produce a fall 

 of snow. And this latter effect is proved, by the accounts sent in 

 from 58 different localities, to have occurred heavily almost through- 

 out the countiy. About the same date, and for some days after- 

 wards very stormy weather was reported from various stations in 

 Italy, where the wind was mostly the Scirocco, the south-easter, 

 which there can be little hesitation in accepting as identical with 

 the Fohn. 



The researches of Ehrenberg on the microscopic organisms con- 

 tained in the red dust and "blood-rain" sometimes deposited by 

 the Scirocco, are strongly in favour of ascribing to them a South- 

 * Ueber Eiszeit, Fohn, uud Scii-occo, von H. W. Dove. Berlin, 1867. 



