1830.^ 
La Chevrette in the India Seas. 
1 5S 
a plan of the harbour of K aits and of its vicinage. In the voyage to Batavia the 
same officer has observed a sufficient number of points to afford several important 
corrections, both in the maps of the Straits of Sunda and in those of the north of 
Java. The road at Batavia lias also been the scene of his indefatigable zeal. 
La Chevrette was furnished with a complete collection of magnetical instruments, 
for the purpose of making a series of observations on land. Ihese instruments 
were verified at Paris before her departure ; they have been also examined since 
her return. During the voyage they were always used wherever the ship touched. 
The expedition has then made us acquainted with the amount of the declination, 
inclination, and magnetic intensity of the needle at Toulon. Isle of Bourbon, Pon- 
dicherry, Calcutta, Chandernagore, Rangoon, Donabieu, Karical, Trincomalee, Jaff- 
napatam, Aripo, Cliangani, Batavia, and Simon’s Town. All these observations 
have been made with the greatest care ; at each place the accordance of the different 
needles has been quite equal to what an observer in a fixed observatory covdd hope 
for. The observations of the horizontal needle will serve to fix the line of no de- 
clination : those of the vertically suspended needle will be not less useful, and will 
enable us to trace the magnetic equator, the position of which, in India, has hitherto 
rested on certain ancient and rather imperfect observations. The discussion of these 
valuable results will doubtless confirm what has been already observed as to the 
gradual shifting of the line of no inclination from east to west: they may even 
serve to decide a question as yet involved in doubt — that is, whether the move- 
ment of this curve is accompanied by any change in its figure. 
The attentive examination we have made of the observations for determining 
the magnetic intensity, has shown us that their discussion will be attended with 
some difficulty, the needles having in fact, all of them, had their magnetism impair- 
ed during the voyage ; but the attention that was given to these observations at 
Pondicherry during the different visits made to that place, with the series obtained 
at Paris to be compared with those in the beginning of 1829, will afford data, we 
hope, for determining the law of the decrease, so as at least to give results that 
shall be comparable. Your commission cannot pass to the next article of their re- 
port without recording here the names of those who have most diligently studied 
the magnetic phenomena. We may therefore state, that the observations at Paris, 
made in 1827 and 1829, are by M. de Blossville ; those made at Toulon before the 
departure of the expedition, by the commander and the young lieutenant we have 
just named. 
The mefereological observations made on board La Chevrette daring her differ- 
ent passages, will be found to constitute one of the most interesting additions 
made to science for many years back. These observations have been registered 
with the greatest care, and are contained in four volumes ; the instruments employed 
had been compared with correct standards before the departure of the expedition ; 
they have been also verified since its return. The errors arising from the radiation 
of the vessel have been carefully guarded against. To form some opinion of the 
extent of these labours, it may be sufficient to be told that the temperature of the at- 
mosphere and that of the ocean have been registered every hour as well during the 
night as during the day throughout the voyage. The barometer has been observed 
regularly during thirteen months, generally 12 or 15 times a day, sometimes 
every half hour, and in a few cases every 10 minutes. So many observations 
must give us a more correct idea of the mean height of the barometer at the 
level of the sea, and on the length of the diurnal period of change at a distance 
from the shore ; that is to say, in such situations as are subject to but small atmos- 
pherical vicissitudes in the 24 hours. We shall also he able to determine 
whether Flinder’s remark, made in New Holland, of the difference of effect on the 
height of the barometer, occasioned by sea and land winds, be equally applicable 
to the Indian seas. A few series of comparative observations, made at sea with 
thermometers having their bulbs whitened and blackened, will have the more 
interest, inasmuch as Captains Parry and Franklin having made some experiments 
of this kind in their polar voyages, it has been thought to be deducible from 
them that the solar rays have less force as we approach the equator. Philoso- 
phers will also be pleased to learn that our navigators have determined the 
temperature of the sea at great depths, by means of well constructed self-regis- 
tering thermometers. These experiments are particularly curious, inasmuch as 
they assist us in enquiring how the inferior strata of the ocean acquire such 
much lower temperatures than what is accountable for by radiation from the 
surface. They have even a greater claim on our attention, inasmuch as it seems 
to be more than probable (judging from some recent observations) that salt 
water has not like fresh its maximum density at a temperature above that of its 
