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 preclude 

 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 is not 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 Atmosphere. 



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 to a 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. 



Elevation 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 difierence of a degree. 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°. 



