230 M. C. Martins on the Nature and Origin of 



analogy to the former is confined to the circumstance of their 

 tilling the atmosphere, and disturbing, like them, the trans- 

 parency of the air ; but aqueous vapour has no part in their 

 formation. Although noticed in meteorological registers, 

 and mentioned by travellers, these fogs have not hitherto 

 been the subject of a comparative study. Accordingly, their 

 history is very little known ; and it is probable that, under 

 the name of dry fogs, meteorological phenomena of very dif- 

 ferent natures have been confounded. The object of the 

 present notice is to distinguish four very distinct kinds of 

 dry fogs, to point out their differential characters, and to call 

 the attention of meteorologists to the consideration of them. 



I. Dry fogs produced by the smoke arising from the burn- 

 ing of peat. 



These fogs have been observed principally in Holland and 

 western Germany. Munck, in the article Dry Fog (Trockner 

 Nebel), in Gehler's Dictionary, and Kaemtz, under the title 

 Hoeherauch, have given a satisfactory view of the ascer- 

 tained facts. Before their time L. L. Fincke had devoted a 

 particular work to this subject. I shall content myself by 

 giving in this place a summary idea of the appearances of 

 this kind of fog and its causes, in order that we may be in 

 a condition to distinguish it from the others. 



The dry fog of German meteorologists is not, properly 

 speaking, a fog, but a smoke spread over a great extent of 

 country. The report on this subject made at the meeting of 

 German naturalists at Berlin, in 1828, by Professor Egen of 

 Scest, informs us how this fog is generated, elevated and 

 diffused in the atmosphere. In the countries which form a 

 belt about 11 myriametres broad, from Zuyder-Zee to the 

 mouth of the Elbe, and over a surface of 430 square myria- 

 meters, there are 107 of these, or a fourth part, occupied 

 with peat-bogs. The proportion is not in all places the same ; 

 in the region lying along the banks of the Ems, from Prus- 

 sia to East Friesland, they form a third part of the surface 

 of the country ; in Eastern Friesland and the Duchy of Olden- 

 burg, a fourth part ; in the territory of Breme and Verden, 

 only a sixth part. These bogs afford no other produce than 

 peat, unless they are burned, or dried by means of drains or 

 canals, which arc very expensive. This last method requir- 



