426 
SURVEY OF THE INTERTROPICAL 
1820. daily range of the thermometer was as much as 
Oct75. 20°, while the mercury on board did not rise or 
fall more than 3° or 4°. This great difference is 
to be attributed to the cooling power of the dew, 
which was precipitated most copiously every 
night upon the surface of the earth ; whilst the 
water, not being so easily affected by this nightly 
radiation, took so much longer to cool. In the 
day-time the reverse took place ; for the earth 
being much more heated by the action of the 
sun’s rays than the water, the temperature on 
shore was much greater than on the sea. 
We had no thermometer with us that could 
measure the heat of the sand upon which our 
tents were erected. Mr. Hunter placed his 
pocket-thermometer in it, but the mercury reach- 
ing the top of the tube, which was graduated to 
130°, he was obliged to withdraw it to preserve 
the instrument from being damaged. On one 
occasion we had a hot land-wind from the S.E., 
that veered round as the day advanced to N.E., 
during which the thermometer stood at 96° ; ge- 
nerally, however, we had a fresh sea-breeze from 
the north-west, with clear and fine weather ; but, 
towards the latter part of our visit, we had some 
very cloudy dull days, and a few showers of 
rain: this change hurried my departure; and 
we, considered ourselves fortunate in embarking 
