f 362 ] 
LV. Report made to the Academy of Sciences, 22d of August 
1825, on the Voyage of Discovery, performed in the Years 
1822, 1823, 1824, and 1825, under the command of M. Du- 
PERREY, Lieutenant of the Navy. 
(Commissioners: MM. ve Humeo tot, Cuvier, DEsFONTAINES, 
Corpier, Latreitie, DE Rosser; and Araco, Reporter.) 
[Coneluded from p. 289.] 
Tides. 
THE observations of the tides, in the rapid navigation of 
the Coquille, had for their principal object the ascertain- 
ing the hour of high-water in different ports. The journals of 
the expedition contain all the elements of these determinations. 
On some coasts M. Duperrey remarked that there was 
only one tide in the twenty-four hours. Similar observations 
are recorded in the works of several old navigators; perhaps 
even now they are sufficiently multiplied for it to be possible 
to arrive at some interesting conclusion on the local causes 
which modify so remarkably the general phenomenon. It is an 
inquiry to which M. Duperrey intends to devote himself. 
During the observation of the tides, when the weather was 
calm, experiments were regularly made on board the Coquille, 
for the purpose of determining to what depth it is possible to 
see, where the bottom is of a decidedly white tint: it was in 
some degree a measure of the transparency of the water. The 
apparatus employed was composed of a plank two feet in dia- 
meter, painted white, and having weights attached in such a 
manner that in descending in the water it would remain ho- 
rizontal. The results, as might be expected, were very dis- 
similar. At Offak, in the isle of Waigiou, in calm and cloudy 
weather on the 13th of September, the disc disappeared when 
it had sunk to 18 metres (55 feet). ‘The next day, (the 14th,) 
the sky being clear, we did not lose sight of the same disc till 
at the depth of 23 metres (70 feet). At Port Jackson, the 
12th and 13th of February (it is evident that here the date is 
of importance), we were never able to see the plank at the 
depth of more than 12 metres (36 feet) in a dead calm. 'The 
mean at New-Zealand, in April, was at a metre less. At the 
Isle of Ascension, in January, under favourable circumstances, 
the extreme limits, in a series of eleven experiments, are 28 
and 36 feet. We have reported these results, because they 
belong to interesting questions to which natural philosophers 
haye paid much attention for some years past. 
Geo- 
