SELEXIURETTED HYDROGEN. 251 



other symptoms of disquietness in the deep 

 regions of the globe. In the years noted in 

 history for the appearance of dry fogs, in 

 526, 1721, 1822, and' 1834, several volcanoes 

 were in great activity. The meteorologist, 

 M. Koemtz, reasoning upon this subject, has 

 ascribed the occurrence of the dry fog of 1782 

 to the enormous volumes of smoke produced 

 by the devastations of the burning lava in 

 Iceland, as it descended on its fiery errand: 

 hence he conceives the smoky odour of dry 

 fogs. Several others of these phenomena he 

 attributes to the smoke emanating from the 

 peat-burnings of Westphalia and Germany. 

 A very prevalent opinion, in 1782, was that 

 the tail of a comet had become mixed up with 

 our atmosphere. The learned author of the 

 Bridgewater Treatise on Chemistry (Dr. Prout), 

 appears disposed to ascribe the fatal effects of 

 dry fog to the presence of a very minute quan- 

 tity of one of the most deleterious gases known 

 to chemistry, Seleniuretted Hydrogen. This 

 gas, since the metallic element Selenium is a 

 volcanic product, he conceives to have been 

 discharged by the volcanic eruptions, and to 

 have become widely dispersed, in a state of 

 extreme dilution, through the air. Berzelius, 

 who first discovered this gas, had a painful 

 experience of its virulent powers ; allowing 



