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 recéived 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 than 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 — 
te 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 sareTy Lamp. As the business of mining for coal, has made 
comparatively little 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.+ 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 vi0- 
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 lives 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 the coal 
Pees gee 
Tea, 
Weer ee 
* Phil. Trans. 1819, p. 126. 
Our great repositories of bits I, are as yet chiefly open to the'day 5 and 
the operations are so near the surface of the ground, as to afford little or no opportunity 
‘9r fire-damp to collect. The mines of anthracite are not liable to these accidents- 
