66 COLOUR OF THE SKY. 
Intensity of the Colour of the Sky and Ocean.— 
From the coasts of Spain and Africa to those of 
South America, the azure colour of the sky in- 
ereased from 13° to 23° of Saussure’s cyanometer. 
From the Sth to the 12th of July, in lat. 122° 
and 14° N., the sky, although free of vapour, was of 
an extraordinary paleness, the instrument indicat- 
ing only 16° or 17°, although on the preceding days 
it had been at 22°. The tint of the sky is general- 
ly deeper in the torrid zone than in high latitudes, 
and in the same parallel it is fainter at sea than on 
land. The latter circumstance may be attributed 
to the quantity of aqueous vapour which is con- 
tinually rising towards the higher regions of the 
air from the surface of the sea. From the zenith to 
the horizon, there is in all latitudes a diminution of 
intensity, which follows nearly an arithmetical pro- 
gression, and depends upon the moisture suspended 
in the atmosphere. If the cyanometer indicate this 
accumulation of vapour in the more elevated por- 
tion of the air, the seaman possesses a simpler me- 
thod of judging of the state of its lower regions, by 
observing the colour and figure of the solar disk at 
its rising and setting. In the torrid zone, where 
meteorological phenomena follow each other with 
great regularity, the prognostics are more to be de- 
pended upon than in northern regions. Great pale- 
ness of the setting sun, and an extraordinary dis- 
figuration of its disk, almost certainly presage a 
storm; and yet one can hardly conceive how the 
condition of the lower strata of the air, which is 
announced in this manner, can be so intimately 
connected with those atmospherical changes that 
take place within the space of a few hours. 
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