Paris as It Was and as It Is Part 60

BUREAU DES LONGITUDES.

As members of this Board of Longitude, the first inst.i.tution of the kind in France, LAGRANGE, LAPLACE, LALANDE, Ca.s.sINI,[1] MeCHAIN, BORDA,[1] BOUGAINVILLE, FLEURIEU, MESSIER, BUACHE, and CARROCHe, the optician, had each 8,000 francs (_circa_ . 330 sterling) a year, and the a.s.sistant astronomers, 4,000. Indeed, the professors of that science were in want of pecuniary a.s.sistance for the purpose of forming pupils.

The _Bureau des Longitudes_ is on a more extensive scale, and possesses greater authority than the Board of Longitude in England.

It is charged with the administration of all the Observatories belonging to the Republic, as well as with the correspondence with the astronomers of foreign countries. The government refers to it the examination of memoirs relative to navigation. Such of its members as more specially cultivate practical astronomy in the National Observatories of the capital, are charged to make all Observations which may contribute to the progress of that science, and procure new means for rectifying the tables of the Sun, as well as those which make known the position of the stars, and particularly the tables of the Moon, the improvement of which so essentially concerns the safety of navigation.

The great importance of the last-mentioned tables induced this Board, about three years ago, to propose a premium of 6,000 francs (_circa_ . 250 sterling) for tables of the Moon. LALANDE recommended to BONAPARTE to double it. The First Consul took his advice: and the French now have tables that greatly surpa.s.s those which are used in England.[2] A copy of these have, I understand, been sent to Mr.

MASKELYNE, our Astronomer-Royal at Greenwich.

The Board of Longitude of France, like that of England, calculates for every year Tables or _Ephemerides_, known in Europe under the t.i.tle of _Connaissance des Tems_. The French having at length procured able calculators, are now able to dispense with the English _Ephemeris_. Their observations follow each other in such a manner as to render it unnecessary for them to recur to those of Greenwich, of which they have hitherto made continual use. Since the year 1795, the _Connaissance des Tems_ has been compiled by JeROME LALANDE. At the end of the tables and their explanation, it contains a collection of observations, memoirs, and important calculations. The French astronomers are not a little surprised that we publish no similar work in London; while Paris, Berlin, Vienna, Gotha, and Milan set us the example. It is in the last volumes of the _Connaissance des Tems_ that JeROME LALANDE gives the history of astronomy, where you will find every thing that has been done in this science.

The _Bureau des Longitudes_ also publishes for every year, in advance, the _Annuaire de la Republique_, which serves as a rule for all the almanacks compiled in France. The meetings of the Board are held at the

NATIONAL OBSERVATORY.

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 facade 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 pa.s.sages, 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 circ.u.mstances 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 circ.u.mference 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 pa.s.sage 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 SeDILLAN. 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 ecole 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 cla.s.sed thirty thousand.

The Ca.s.sINIS 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. MeCHAIN, the present director, and BOUVARD, his a.s.sociate, are extremely a.s.siduous in their astronomical labours.

CARROCHe 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 MeCHAIN, 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 surpa.s.s 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 t.i.tle of _Mecanique Celeste_, 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 a.s.sociated 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, LAKa.n.a.l, 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 Inst.i.tute, 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 a.n.a.lytical genius, surpa.s.s 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, MeCHAIN, BOUVARD, and PONS find some. Last year, JeROME 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, MeCHAIN 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 circ.u.mstance 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

NEW FRENCH WEIGHTS AND MEASURES.

Among the great ideas realized during the first period of the revolution, must be reckoned that of a uniform system of weights and measures. From all parts of France remonstrances were sent against the great variety of those in use. Several kings had endeavoured to remedy this evil, which was so hurtful to lawful trade, and favourable only to fraud and double-dealing. Yet what even _they_ had not been able to effect, was undertaken by the Const.i.tuent a.s.sembly.

It declared that there ought to be but one standard of weights and measures, in a country subject to the same laws. The _Academy of Sciences_ was charged to seek and present the best mode of carrying this decree into execution. That society proposed the adoption of the decimal division, by taking for a fundamental unit the ten-millionth part of the quarter of the terrestrial meridian. The motives which determined this choice were the extreme simplicity of decimal calculation, and the advantage of having a measure taken from nature.

The latter condition would, in truth, have been accomplished, had there been taken, as a fundamental unit, the length of the pendulum marking seconds for a given lat.i.tude; but the measure of an arc of the meridian, executed with the precision to be obtained by the methods and instruments of the present day, was extremely interesting in regard to the theory of the figure of the earth. This influenced the decision of the Academy, and if the motives which it presented to the Const.i.tuent a.s.sembly were not exactly the real ones, it is because the sciences have also their policy: it sometimes happens that to serve mankind, one must resolve to deceive them.

All the measures of the metrical system, adopted by the Republic, are deduced from a base taken from nature, the fourth part of the terrestrial meridian; and the divisions of those measures are all subjected to the decimal order employed in arithmetic.

In order to establish this base, the grand and important work of taking a new measure of the terrestrial meridian, from Dunkirk to Barcelona, was begun in 1792. At the expiration of seven years, it was terminated; and the Inst.i.tute presented the result to the Legislative Body with the original table of the new measures.

MeCHAIN and DELAMBRE measured the angles of ninety triangles with the new reflecting circles; imagined by MAYER, and which BORDA had caused to be constructed. With these instruments, they made four observations of lat.i.tude at Dunkirk, Paris, evaux, Carca.s.sonne, and Barcelona; two bases measured near Melun and Perpignan, with rules of platina and copper, forming metallic thermometers, were connected with the triangles of the meridian line: the total interval, which was 9.6738, was found to be 551584.72 toises. As the degrees progressively diminished towards the south, but much more towards the middle than towards the extremities, the middle of the whole arc was taken; and, on comparing it with the degrees measured at Peru, between the years 1737 and 1741, the ellipticity of the earth was concluded to be 1/334 the mean degree, 57008 toises; and the MeTRE, which is the ten-millionth part of the quarter of the meridian, 443.296 lines of the old French toise which had been used at Peru.

The Commissioners, sent from foreign countries, verified all the calculations, and sanctioned the results. The experiments of the pendulum made at the observatory, with extreme care, by BORDA, MeCHAIN, and Ca.s.sINI, with a new apparatus, constructed by LENOIR, shewed the pendulum to be 0.99385 of the _metre_, on reducing it to the freezing point, and in _vacuo_: this would be sufficient for finding again the _metre_, though all the standards were changed or lost.

Exact experiments, made by LEFeVRE-GINEAU, with instruments constructed by FORTIN, shewed the weight of the cubic decimetre of distilled water, at the point of the greatest condensation to be 18827.15 grains of the pile of 50 marcs, which is preserved here in the _Hotel de la Monnaie_, and is called _Le poids de Charlemagne_; the toise being supposed at 13 degrees of the thermometer of 80 degrees. The scales of FORTIN might give a millionth part and more; and LEFeVRE-GINEAU employed in all these experiments and calculations the most scrupulous degree of exactness.

Thus the MeTRE or princ.i.p.al unit of the French linear measures has furnished those of the weights; and all this grand system, taken from nature, is connected with the base the most invariable, the size of the earth itself.

The unit of the measures of capacity is a cube whose side is the tenth part of the _metre_, to which has been given the name of LITRE; the unit of measures of solidity, relative to wood, a cube whose side is the _metre_, which is called STeRE. In short, the thousandth part of a _litre_ of distilled water, weighed in _vacuo_ and at the temperature of melting ice, has been chosen for the unit of weights, which is called GRAMME.

The following TABLE presents the nomenclature of these different Measures, their divisions, and multiples, together with the new Weights, as decreed by the Legislative Body, and to it is annexed their correspondence both with the old French Measures and Weights, and those of England.

LINEAR MEASURES.

FRENCH ENGLISH T F I L M F Y Ft I[A]

Myriametre (or League) 10,000 Metres 5,130 4 5 3.360 6 1 156 0 6

Kilometre (or Mile) 1,000 Metres 513 0 5 3.936 - 4 213 1 10.2

Hectometre 100 Metres 51 1 10 1.583 - - 109 1 1

Decametre (or Perch) 10 Metres 5 0 9 4.959 - - 10 2 9.7