Remarks on the Barometer, &c. 347 
and the ninth, records the state of the weather. When not marked 
reefs, the ship was under full sail. 
The temperature of the air and water were examined by the same 
thermometer, and therefore we may suppose the temperature of the 
air is marked lower than it actually was, as the mercury would fall 
something from the evaporation of the moisture left upon the glass 
after each immersion. 
According to the table, the fluctuations of the barometer do not 
precede the changes of weather, but as Captain Fitzroy remarks, 
seem to accompany them. On the 28th of July, the ship was lying- 
to in a gale, the barometer standing at 29.76 inches ; on the 29th, the 
barometer standing at 30.15, the ship is still lying-to, the weather 
moderating with the rise of the mercury. The barometer having 
fallen in the preceding five days from 30.50 to 29.75, on the 4th 
August, (lower than it was in the gale of the 28th July,) the weather 
was cloudy and the wind moderate. ‘The mercury continued to fall 
until the 11th, when it stood at 28.40, yet in the mean time the | 
weather, though somewhat boisterous, was not so heavy as to require 
the ship to lie-to. The same description of weather was experi- 
enced under almost all the variations of the barometer, though it was 
commonly fair when the mercury stood above thirty inches, but not 
invariably so. 
The observations do not show that the mercury has a regular di- 
urnal flux and reflux, though it was seldom stationary throughout the 
twenty-four hours. 
It would seem, from our present knowledge, that the fluctuations 
of the barometer indicate changes of weather differently in different 
latitudes ; while a rise of the mercury in some regions is followed 
by fresh gales, in others, the same phenomena follow the fall of the 
column. If this be established, it is clear that the barometer is not 
of universal practical use in navigation, but requires to be studied for 
particular regions. 
Though we may generalize from the table before us, the observa- 
tions are too limited to infer any general rules, or establish any one 
fact in relation to the practical use of the instrument ; but, sufficient 
evidence, with very little labor, might very soon be accumulated by 
navigators, to put all questions at rest in regard to it. 
The temperature of the water, both in the Pacific and Atlantic, 
was constantly higher than that of the air, and increased as we ap- 
proached the land at Rio de Janeiro, as well as at Bahia. 
U.S. Ship Peacock, Norfolk, Va., October 27, 1837. 
