Facts in Meteorology. 123 
I am aware that this method of bringing forward truths, or propo- 
sitions, in natural science, is liable to objections; but I have thought 
it better to incite the attention of others to the facts and physics of 
meteorology, by means of such brief statements, rather than to at- 
tempt a systematic demonstration of this extensive and_ interesting 
subject, under circumstances which, on my part, seem to peeabede 
such an undertaking. 
The favorite and hitherto prevailing theory, or hypothesis, is that 
which makes equatorial heat and rarefaction, to be the principal cause, 
the grand primum mobile, of winds ; and which assigns local rarefac- 
tion as the immediate cause of great storms. If this theory should 
seem to be invalidated in any degree, by these statements, or by any 
‘that have been previously made, the fault isnot mine. Facts in na- 
ture are strangely unaccommodating, in relation to some opinions, 
and modes of thinking which the writer, in common with your read- 
ers, has been accustomed to cherish. 
General view of the eae 
The superficial extent of the atmosphere at its lower surface, is 
equal to about 200,000,000 of square miles. Its altitude, if reckon- 
ed at the uniform density of its lower surface, or in other words, ac- 
cording to its actual quantity, is equal toa little more than five miles. 
Considered, therefore, as a fluid stratum resting upon the earth, the 
horizontal or superficial extent of the atmosphere is to its altitude or 
vertical dimensions, in the proportion of near 40,000,000 to 1 ; which 
shows its relative thickness to be less than that of a sheet of paper, 
when compared with its surface, a fact that well deserves considera- 
tion in any physical estimate of its winds and currents. 
Temperature of Elevation. 
Flsvone above the level of the sea, or the general level of a coun- 
try, makes a regular variation in temperature ; the first 300 feet, it is 
supposed, causes a difference of adegree. After ascending 300 feet, 
we are told, the thermometer falls a degree at 295 feet, then at 277, 
252, 223, and at 192 feet; so that at 1539 feet of elevation, the 
thermometer will fall six degrees in a general way ; but 300 feet 
per degree is the common rule. On these principles, the limit of 
perpetual congelation has been theoretically calculated : it is made 
15000 feet at the equator ; and from that to 13000 between the trop- 
ics; and from 9000 to 4000 between latitude 40° and 59°. 
