130 Mr. Colebrooke’s Meteorological Observations 
frequent in the ¢rade-winds, and still more common beyond 
their limits, appears to influence but slightly either the thermo- 
meter or hygrometer. It is a passing mist, or showery scud; 
or a low drift-cloud, sweeping the surface of the sea. A tran- 
sient puff of wind attends it; and it is often succeeded by a 
short lull. But the humidity and temperature of the air undergo 
slight variation during its brief passage, and exhibit no con- 
siderable change after its transition ; though doubtless the at- 
mosphere is in both respects, materially affected by the frequent 
recurrence of showery squalls. 
Mists, (not dry fogs, but wet or moistening), have a manifest 
influence on the hygrometer. In this case, saturation, or all 
but saturation, is exhibited. They are in fact the consequence 
of extreme humidity. 
A heavy shower draws down air with it. Both the rain, and 
the air attendant on it, bring with them the temperature of the 
higher atmospheric strata, from which they descend. In the 
tract of variable winds, situated between the frades, rain is 
heavy ; and it is there not unusually accompanied by decrease 
of temperature, amounting to 4° or 5°: a difference of 6° and 
even 62° has been observed. Hygroscopie indications at the 
same time are those of increased moisture; from 4° or 5° (.12 
or .15) of dryness, before a shower, to 1° or 2° (.3 or .6) after it. 
A passing shower, especially a heavy one, is preceded by a 
gust of cold air; and not unfrequently succeeded for a while by 
one, in the contrary direction: because the rain drags along with 
it air from an upper and cooler stratum of the atmosphere; and 
that air diffuses itself on all sides of the rainy column. 
Long continued rain is comparatively unfrequent on the open 
ocean. Its effect, where it does occur, is no doubt to saturate 
the lower atmosphere with moisture ; and such appears to have 
been the result in the few instances which came under notice. 
Low clouds, whether scud or mist, participate the hygrometric 
condition of the inferior atmosphere ; and the clouds hang low, 
in proportion as the air approaches to saturation of moisture. 
They touch the sea’s surface if it be complete. Their course 
agrees with that of the wind. 
