240 Scientific Labors and Character of 



In a passage on the Danube, the attention of Sir Humphry was 

 attracted towards the morning fogs that hang over rivers, and he was 

 led to investigate the circumstances, and to propose an explanation 

 which is generally received in meteorology as the true theory of 

 Mists.* His explanation however we cannot but consider as erro- 

 neous. The true cause we believe to be this : a fog is formed when- 

 ever watery vapor rising from the earth meets with colder air, which 

 condenses it. Now a large river like the Danube, does not become 

 sensibly colder during the night than it was the preceding day, but 

 continues to send off vapor nearly in the same quantity. But the air 

 over the land becomes a number of degrees colder at night tlian by 

 day ; and the vapor coming into contact with the colder air, is con- 

 densed into fog. Sir Humphry supposes the fog to be produced as 

 follows : the air over the river, by the influence of the stream, re- 

 mains warmer than the air over the land on each side ; and the cold- 

 er and the warmer portions of air being mixed, the fog is precipitated 

 from the latter. But this phenomenon takes place over rivu- 

 lets, the breadth of which is so small that we cannot suppose the 

 temperature of the incumbent air, to be at any moment essentially 

 different from that of the banks. 



The year 1815 was rendered memorable by the invention of 

 the SAFETY LAMP. As the business of mining for coal, has made 

 comparatively httle progress in our country, we have had no occa- 

 sions to witness the terrible disasters so common in England, against 

 which the safety lamp affords protection. f A species of carburetted 

 hydrogen gas, called by the miners fire-damp, is extricated in the 

 coal mines of that country, which, on being mixed with atmospheric 

 air, takes fire from the flame of a lamp, and explodes with the vio- 

 lence of a magazine. The explosion that occurred at the Felling 

 colliery in the year 1812, when one hundred and one persons sud- 

 denly lost their hves under aggravated horrors, filled all the coal dis- 

 tricts of England with terror and dismay. Several methods had 

 been devised to obviate these formidable dangers, but they had all 

 proved either ineffectual, or inapplicable to common use. The poor 

 miners were left to grope their way in the dark caverns of tlie coal 



* Phil. Trans. 1819, p. 126. 



t Our great repositories of bituminous coal, are as yet chiefly open to the day ; and 

 the operations are so near (he surface of the ground, as to afford little or no opportunity 

 for fire-damp to collect. The mines of anthracite are not liable to these accidents. 



