Meteorological Sketches. 261 
who looks up, after having for some time gazed down upon the path 
he is walking in, the black soil of which is strongly contrasted with 
the bleached grass on either side. 
Whoever will attentively watch the operation of this principle, in 
experiments which he can make almost any where and with very 
little trouble, will, we think, be abundantly satisfied that it must 
have acted no inconsiderable part, in keeping alive those supersti- 
tious impressions which in former ages have been so generally prev- 
alent, and that it is the talisman which raises some at least of the 
apparitions that are occasionally alarming the young and the super- 
stitious, at the present day. 
5. Q. P. 
New Haven, March 8, 1837. 
Arr. Xl.—WMeteorological Sketches. 
(Continued from p. 65.) 
Of Deserts. 
Tue atmosphere is capable of absorbing aqueous vapor in pro- 
portion to its temperature, and as a current of air in passing from a 
colder to a warmer region necessarily increases in temperature, it 
thus acquires an increasing capacity for moisture, which tends to 
prevent the formation of clouds and rain. ‘This condition pertains 
not only to currents which descend from high mountains and sweep 
over elevated plains, but is peculiar to a certain section or portion 
of the great natural circuits of wind which are found in various re- 
gions, on both sides of the equator. ‘The necessary consequence, is 
a scarcity of rain in this portion of the aerial current, or in those 
places where the winds from the temperate or extra-tropical latitudes 
are found blowing towards the equator, either uniformly, or for reg- 
ular and determinate periods. We perceive here the principal cause 
of those arid deserts, comprising almost every variety of geological 
formation, which occupy so large a space in the otherwise most fruit- 
ful latitudes. 
On examining the map of the world, it may be seen that this ab- 
sence of rain is found chiefly in countries lying between the 18th 
and 32d parallels of latitude, and situated upon the eastern side of 
the great oceans or of the great circuits of wind which are found to 
Vou. XX XITLL—No. 2. 34 
