PSS oe 
FROM THE HIGHER ATMOSPIERE. 49] 
exchange of influence must evidently tend to accelerate that 
progress to an equilibrium which the gradual intermixture of 
the different strata, if left quite undisturbed, would in time 
produce. The air of a close apartment, exposed to the action 
of a steady fire, is hence kept agitated through its whole mass 
by a series of opposite tremors, which continually disperse, in 
all directions, the irregularities of temperature. 
_ If the action of the pulses excited in the air of a small room 
be made thus apparent, how much more striking should we 
expect to find the effect produced by the mingled tide of 
commotion collected from the vast body of the atmosphere 
itself? Taking even the lowest range of strata, to the height 
perhaps of two miles, including scarcely one-third part of 
the whole aérial mass, the difference of temperature between 
its extreme boundary will amount to 20 centesimal degrees, 
or 36 on Fahrenheit’s scale. The order of the series, however, 
is exactly the reverse of what takes place in a close room, the 
air of the superior regions being invariably colder than at the 
surface of the earth. Accordingly, the simple pyroscope, ex- 
posed in calm weather to a clear and open sky, will, at all 
times, if not disturbed by the influence of a strong light, indi- 
cate large impressions of cold, amounting to 5 or perhaps even 
10 degrees. In most cases, it may be sufficient to screen this 
instrument from the direct action of the sun’s rays. But the ac- 
tion of light will be almost neutralized, by opposing a diapha- 
nous ball to one gilt with silver, or contrasting a ball of the 
different shades of green or blue, to another coated with pure 
gold leaf. But to procure consistent results, it is still more 
necessary to guard against the deranging influence of winds. 
The same sectoral form of the athrioscope discloses also the 
peculiar influence of clouds in obstructing the frigorific pulses 
excited in the atmosphere. When the sky was completely ob- 
scured by a dense canopy of clouds, the instrument being 
3Q2 pointed 
