This edifice, which is situated at the farther end of the _Faubourg
St. Jacques_, was constructed in 1664, by order of COLBERT, and
under the direction of PERRAULT, the medical architect, who planned
the celebrated façade of the _Louvre_.
The form of the building is rectangular. Neither wood nor iron have
been employed in its construction. It is arched throughout, and its
four sides stand exactly in the direction of the four cardinal points
of the horizon. Although its elevation is eighty-five feet, it
comprises but two stories, terminated by a flat roof, whence you
command a fine view of Paris. You ascend thither by a winding
staircase which has a hollow newel. This staircase, consisting of
three hundred and sixty steps, extends downward to a similar depth of
eighty-five feet, and forms a sort of well, at the bottom of which
you can perceive the light. From this well have been observed the
different degrees of acceleration in the descent of bodies.
The subterraneous vaults have served for meteorological experiments.
In one of them water is seen to petrify on filtering through the rock
above. They lead to near fifty streets or passages, formed by
quarries excavated in procuring the stones with which great part of
the city of Paris is constructed.
Previously to the year 1777, churches, palaces, whole streets of
houses, and the public highway of several quarters of Paris and its
environs, were on the point of being swallowed up in gulfs no less
vast in depth than in extent. Since then, considerable works have
been undertaken to consolidate these subterraneous caverns, and fill
up the void, equally dangerous, occasioned by the working of the
plaster-quarries.
An accident of a very alarming nature, which happened in the _Rue
d'Enfer_ in the year 1774; and another, at Montmenil, in 1778, shewed
the necessity of expediting these operations, which were followed up
with great activity from 1777 to 1789, when their progress was
relaxed from the circumstances of the times. These quarries are far
more extensive than is commonly imagined. In the department of the
Seine alone, they extend under all the south part of Paris, and the
roads, plains, and _communes_, to the distance of several leagues
round the circumference of this city. Their roof, with the edifices
standing on the soil that covers it, is either supported by walls
recently built under the foundation of those edifices, or by pillars
constructed at different periods in several places. The government is
at the expense of providing for the safety of the streets, highways,
and public buildings, but that of propping under-ground all private
habitations must be defrayed by the proprietor. These ancient
quarries had been much neglected, and the means of visiting them was
equally dangerous and inconvenient. At present, every precaution is
taken to insure the safety of the persons employed in them, as well
as the stability of their roof; and for the better superintendance of
all the subterraneous constructions of Paris, galleries of
communication have been formed of sufficient width to admit the free
passage of materials necessary for keeping them in repair.
Let us now find our way out of these labyrinths, and reascending to
the surface of the soil, pursue our examination of the Observatory.
In a large room on the first floor is traced the meridian line, which
divides this building into two parts. Thence, being extended to the
south and north, it crosses France from Colieure to Dunkirk.
On the pavement of one of the rooms is engraved a universal circular
map, by CHAZELLES and SÉDILLAN. Another room is called the _Salle aux
secrets_, because on applying the mouth to the groove of a pilaster,
and whispering, a person placed at the opposite pilaster hears what
is said, while those in the middle of the room, hear nothing. This
phenomenon, the cause of which has been so often explained, must be
common to all buildings constructed in this manner.
In speaking of the _Champ de Mars_, I mentioned that LALANDE obtained
the construction of an Observatory at the _ci-devant École
Militaire_. Since 1789, he and his nephew have discovered fifty
thousand stars; an immense labour, the greater part of them being
telescopic and invisible to the naked eye. Of this number, he has
already classed thirty thousand.
The CASSINIS had neglected the Observatory in Paris; but when LALANDE
was director of this establishment, he obtained from BONAPARTE good
instruments of every description and of the largest dimensions. These
have been executed by the first artists, who, with the greatest
intelligence, have put in practice all the means of improvement which
we owe to the fortunate discoveries of the eighteenth century. Of
course, it is now as well provided as that of Greenwich. MÉCHAIN, the
present director, and BOUVARD, his associate, are extremely assiduous
in their astronomical labours.
CARROCHÉ has made for this Observatory a twenty-two feet telescope,
which rivals those of HERSCHEL of the same length; and the use of
reflecting circles, imagined by MAYER, and brought into use by BORDA,
which LENOIR executes in a superior manner, and which we have not yet
chosen to adopt in England, has introduced into the observations of
the French an accuracy hitherto unknown. The meridian from Dunkirk to
Barcelona, measured between the years 1792 and 1798, by DELAMERE and
MÉCHAIN, is of an astonishing exactness. It has brought to light the
irregularity of the degrees, which was not suspected. The rules,
composed of platina and copper, which LAVOISIER and BORDA imagined
for measuring bases, without having occasion to calculate the effect
of dilatation, are a singular invention, and greatly surpass what
RAMSDEN made for the bases measured in England.
LAPLACE has discovered in the Moon inequalities with which we were
not acquainted. The work he has published, under the title of
_Mécanique Céleste_, contains the most astonishing discoveries of
physical theory, the great inequality of Jupiter and Saturn, the
acceleration of the Moon, the equation of the third Satellite of
Jupiter, and the flux and reflux of the sea.
BURCKHARDT, one of the associated members of the _Bureau des
Longitudes_, is a first-rate astronomer and a man of superior talent.
He is at present employed on the difficult task of calculating the
very considerable derangements of the planet discovered by OLBERS at
Bremen, on the 28th of March 1801.
VIDAL has made, at Mirepoix, more observations of Mercury than all
the astronomers for two thousand years past, and these are the most
difficult and uncommon.
DELAMBRE has computed tables of the Sun, of Jupiter, of Saturn, and
of Herschel; LALANDE, the nephew, has composed tables of Mars; and
his uncle, of Mercury, which never deviate more than a few seconds
from the observations.
Even during the reign of terror, astronomy was not neglected. Through
the interest of CARNOT, CALON, LAKANAL, and FOURCROY, the _Bureau de
Consultation des Arts_ gave annually the sum of 300,000 francs
(_circa_ £12,000 sterling) in gratifications to artists.
Afterwards, in 1796, the National Institute, richly endowed, proposed
considerable premiums. LALANDE, the uncle, founded one for astronomy;
BONAPARTE, another for physics; and the First Consul has promised
60,000 francs (_circa_ £2,800 sterling) to any one who shall make a
discovery of importance.
France can now boast of two young geometricians, BIOT and PUISSON,
who, for analytical genius, surpass all that exist in Europe. It is
rather extraordinary that, with the exception of Mr. CAVENDISH and
Dr. WARING, England has produced no great geometricians since the
death of MACLAURIN, STERLING, and SIMPSON.
The French tables of Logarithms, printed stereotypically, are cleared
of all the errors which afflicted calculators of every country. Those
of other nations will owe this obligation to Frenchmen.
HERSCHEL no longer looks for comets; but the French astronomers,
MESSIER, MÉCHAIN, BOUVARD, and PONS find some. Last year, JÉROME
LALANDE deposited 600 francs in the hands of his notary, as a premium
to stimulate the efforts of young observers.
* * * * *
_February 11, in continuation._
In the spring of 1803, MÉCHAIN will leave Paris for the purpose of
extending his meridian to the Balearic Islands. He will measure the
length of the pendulum in several places, in order to ascertain the
inequality of the earth which the measure of the degrees had
indicated. This circumstance reminds me of my neglect in not having
yet satisfied your desire to have a short account of the means
employed for fixing the standard of the