different kinds of Dry Fogs. 233 



the east and north-east : in Westphalia, by the north-west, 

 north, or north-east ; at Goettingen, where it has been studied 

 by MM. Gauss and Haussmann, by the north and north- 

 west ; at Jever, by the south. There are no doubt excep- 

 tions ; they are caused by shifting winds, which do not allow 

 us to ascertain the original direction of the current which 

 brought the smoke. 



6. The most evident proof of the origin of the Land- 

 rauch is that, in most cases, we can prove the coincidence of 

 great combustions with the appearance of the dry fog. Thus, 

 on the 18th and 19th of June 1821, about mid-day, the peat- 

 bog was enveloped in a thick cloud of smoke ; about live 

 hours after, the countries between the North Sea and Siegen, 

 and between Cleves and Minden, were likewise covered with 

 smoke. On the 22d May 1822, in the morning, the peat 

 was concealed by the smoke ; about six o'clock, all the 

 country between the North Sea and Coblentz, and between 

 Arnheim and Minden, was occupied by it. This is a surface 

 of 1035 square myriametres. In reference to that day M. 

 Egen received notice from forty-two localities comprised in 

 that space. 



The same observer has further satisfied himself by hygro- 

 metrical experiments, in which he made use of Darnell's 

 hygrometer, that the humidity of the air was not greater 

 during the dry fog than on the days which preceded and 

 followed its appearance. August at Berlin, and Kaemtz at 

 Halle, made the same experiments and obtained the same 

 results on the dry fog of 1834. 



These facts appear to us sufficient to establish the origin 

 of certain dry fogs. One point alone remains to be deter- 

 mined, namely, whether this smoke can be transported to 

 great distances without being dissipated, and give rise to 

 the appearance of the dry fogs which have been noticed 

 principally in Holland, Western Germany, and the north of 

 France. Many authors have decided this point in the 

 affirmative. Fincke has traced it for the space of 22 myria- 

 metres without its intensity being diminished. The greater 

 part of German meteorologists, such as Egen and Kaemtz, 

 believe that the smoke arising from the combustion of peat 



