ot 
493 THERMOMETRICAL JOURNAL. 
June 1785. The mean there was 73 while to the north- 
ward and fouthward the thermometer marked 77. 
Returning towards the coaft of America, Captain Bil- 
lings difcovered his paflage acrofs the gulph ftream by a 
fudden fall i in the mercury of 5° from noon to night, and 
about 5° farther Weft, by a further fall in the foace of 8 
hours run, he difcovered the coaft, where he got foundings, 
before he faw the land. 
The ufefulnefs of the thermometer as a nautical inftru- 
ment is not confined to the difcovery of an approach to- 
wards objects of danger known to exif?; but it, may if at- 
tended to, difcover others not at prefent fuppofed to exit, 
againft which a navigator cannot be on his guard. Seve- 
ral charts, particularly one made by Governor Pownall, in 
September 1787, point out rocks and breakers in the mid- 
dle of the ocean; fome are faid to be uncertain, others 
have been feen but once, and preferve the names of their 
fuppofed difcoverers. ‘Thefe facts are generally doubted, 
and by fome mariners have been ridiculed; but it fhould: 
be confidered that in every inftance where the difcovery of 
thefe hidden dangers have been fatal, no one could efcape 
to tell the melancholy tale, and furely the number of mif+ 
fing fhips juftifies a conjecture that fuch misfortunes have 
happened, and ought to influence every navigator to make 
accurate obfervations on the temperature of the fea during 
the whole of his voyage. 
A gentleman of undoubted veracity related to me fome 
time fince, the following fa&, which I mention on ac-' 
count of its aptitude to this fubject. 
On a voyage from the Weft-Indies to England, the 
fmall veffel hie was in, touched at Bermuda. On leaving: 
that ifland, having fine weather and a fmooth fea, they 
failed along a ridge of rocks, feeing the bottom very plain- 
ly 
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