THE EQUATORIAL CLOUD-RING. 
177 
356. In the process of condensation, these rain-drops, on the 
other hand, have set free a vast quantity of latent heat, which has 
been gathered up with the vapor from the sea by the trade-winds 
and brought hither. The caloric thus liberated is taken by the 
air and carried up aloft still farther, to keep, at the proper distance 
from the earth, the line of perpetual congelation. Were it possi- 
ble to trace a thermal curve in the upper regions of the air to rep- 
resent this line, we should no doubt find it mounting sometimes at 
the equator, sometimes on this side, and sometimes on that of it, 
but always so mounting as to overleap this cloud-ring. This 
thermal line would not ascend always over the same parallels : it 
would ascend over those between which this ring happens to be ; 
and the distance of this ring from the equator is regulated accord- 
ing to the seasons. 
357. If we imagine the atmospherical equator to be always 
where the calm belt is which separates the northeast from the 
southeast trade-winds, then the loop in the thermal curve, which 
should represent the line of perpetual congelation in the air, w^ould 
be always found to stride this equator and it may be supposed 
that a thermometer, kept sliding on the surface of the earth so as 
always to be in the middle of this rain-belt, would show very nearly 
the same temperature all the year round ; and so, too, would a 
barometer the same pressure. 
358. Its Office. — Returning and taking up the train of contem- 
plation as to the office which this belt of clouds, as it encircles 
the earth, performs in the system of oceanic adaptations, we may 
see how the cloud-ring and calm zone which it overshadows per- 
form the office both of ventricle and auricle in the immense atmos- 
pherical heart, where the heat and the forces which give vitality 
and power to the system are brought into play — where dynamical 
strength is gathered, and an impulse given to the air sufficient to 
send it thence through its long and tortuous channels of circulation. 
359. Thus this ring, or band, or belt of clouds is stretched 
around our planet to regulate the quantity of precipitation in the 
rain-belt beneath it ; to preserve the due quantum of heat on the 
face of the earth ; to adjust the winds ; and send out for distribu- 
tion to the four corners, vapors in proper quantities to make up to 
each river-basin, climate, and season, its quota of sunshine, cloud, 
and moisture. Like the balance-wheel of a well-constructed chro- 
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