every conception, every view, and every thought; which knowing neither human infirmities, nor the decay of the senses and of old age, ever young and ever active, scrutinizes incessantly the hidden properties of nature, discovers the powers concealed in them, and at last offers them to society perfected and prepared for application. In this centre, where all opinions are agitated and combated, no authority can prevail but that of reason and nature. Here even the voice of a Plato could no longer attract listeners to the brilliant dreams of his imagination; and the genius of a Descartes, obliged to continue faithful to the method of observation and of doubt which he himself had created, could only produce truths unmixed with error. But Plato and Descartes, with all their glory, would now be considered but as transient elements of this great organ of the sciences. Its strength would survive their genius, and would pursue into futurity the development of their thoughts. Such is now the noble destination of learned societies. The unity and the duration, which their institution gives to human efforts, complete the power of the experimental method. They alone can henceforth ensure the continuity of the progress of human knowledge, they alone can develop great theories, and obtain results which, by their intrinsic difficulty, and by the diversity, the perseverance, and the extent of the labours they demand, could never be within the reach of individuals. The determination of the size and figure of the earth,-the measurement of gravity at its surface,-the connexion of this phenomenon with the interior construction of the globe, with the disposition of the strata, and the laws of their densities,-are of the number of those long enduring questions which learned societies alone could propose to encounter and to resolve. They have for a century and a half formed one of the objects of the unceasing labours of the Academy of Sciences. The first exact measurement of a degree of the terrestrial meridian, was made in France, by Picard, in the year 1670. Newton availed himself of it, in order to establish the law of universal gravity, from which the employment of an inaccurate measurement of the earth had at first caused him to wander. Two years afterwards, Richer, who was, sent by the Academy to Cayenne, to make astronomical researches, discovered that his clock, which at Paris, beat the seconds, went gradually more slowly as he approached the equator; and that it again went quicker, by the same degrees, in returning towards the north, so as to resume exactly its original motion, at the point of his departure. Again, according to the discoveries of Huygens, the quickness of the oscillations of a pendulum augments or diminishes with the intensity of the gravity which causes its motion. The observation of Richer then, proved that this intensity was different in different latitudes, and that it increased in going from the equator to the pole. Newton, in his immortal work on the principles of Natural Philosophy, connected all these results with the law of attraction. He showed, that the variation observed in gravity disclosed a flat.

tening of the earth at the pole, a circumstance which is observable also in the form of Jupiter, Saturn, and the other planets which turn upon an axis. He conceived that this flattened form was a consequence of the even attraction of the portions of every planet, combined by the centrifugal force of its rotatory motion. But in order that the arrangement determined by these two kinds of forces should thus have been able to make itself effectual, it behoved these great bodies to have been originally fluid: he took them then as in that state, and showed how to calculate the flattening of a planet according to the intensity of the gravity at its surface, and the quickness of its rotation, supposing its mass to be homogeneous. This theory, applied to the earth, gave a variation of gravity, but little different from that observed by Richer, though somewhat slighter, indicating that the earth is composed of strata, of which the density goes on increasing from the surface to the centre, as Clairault has since demonstrated.

The calculations of Newton were, for some time, the only inductions which existed for believing the earth to be flattened at the poles. The arch of the meridian, measured by Picard, was quite sufficient to give the length of the semi-diameter of the earth at the place where it was observed; but that arch was much too small even for showing imperfectly the effect of the flattening. More accurate knowledge was expected to be procured from the measurement of the complete arch which traverses France from Perpignan to Dunkirk; a measurement which was intended to serve, if I may so express it, as the axis of a general map of France, with the executing of which, Colbert had entrusted the Academy. But in the imperfect state of the instruments and astronomical methods of that period, this arch itself was too short to make the influence of the flattening distinctly perceptible; and the small variations, which thence result in the lengths of the consecutive degrees, might very easily be lost in the errors of the observations. This indeed happened. The differences which the degrees presented, were found from the effects of these errors, in such a direction as would have led to the result of elongation at the poles, in place of flattening. The Academy was not disheartened; it perceived that the question could not be clearly decided without measuring two arches of the meridian, in regions of the earth where the flattening must produce more sensible differences between the degrees, that is to say, near the equator and the pole. She found among her members, men sufficiently devoted to undertake these laborious journies. In the year 1735, Bouguer, Godin, and La Condamine, went to America, where they joined the Spanish commissioners. Some months after, Clairault, Maupertuis, and Le Monnier, departed for the north. The results of these expeditions put the flattening of the earth beyond doubt, but its absolute amount still remained uncertain. The degree of Peru, compared with that of France, gave a slighter flattening than if the earth were homogeneous; the operation of Lapland indicated

a greater. In this uncertainty, the lengths of the pendulum, which they were careful to measure, agreed with the flattening deduced from the operation at the equator; but the exactness of these measurements, especially in the operation of Lapland, was not such as could enable them to solve the difficulty. No fault lay with any one, as at that period it was impossible to do it better.

Things remained at this point during fifty years. Bouguer, La Condamine, Clairault, and Maupertuis, died; but after that interval, astronomical instruments becoming much more perfect, and the methods of observation more general and more precise, hopes were entertained of removing the uncertainty which preceding operations had left on the flattening of the earth. The Academy, the heir of these great works, resolved to resume them with all the means which could ensure their success. She gave still more importance to them, by proposing to take the very size of the earth, thus determined, for the fundamental element of a system of general and uniform measures, of which all the parts would be connected together by simple relations, and in accordance with our mode of numeration. At this day, as formerly, she hopes that such a system, founded upon natural elements, invariable and independent of the individual prejudices of the people, will ultimately become as common to all, as are now the Arabian ciphers, the division of time, and the calendar. It was a wish long ago, expressed by the best and most enlightened of our kings. The proposal realizing it, was, so to speak, the last sigh of the Academy; and the act which decided its execution, was one of the last which preceded the fatal epoch of our great political convulsions. All the institutions tending to maintain civilization and knowledge perished, and the Academy perished with them. But true men of science do not require to have repeated to them the authority for doing that which they believe useful. In the midst of the disorder and madness excited by popular anarchy, MM. de Lambre and Méchain, furnished with new instruments which Borda had invented for them, began, and continued, often at the risk of their lives, the most extended and exact measurement of the earth which had ever been undertaken. They concluded it as well, although not so easily, as they could have done in the bosom of the most profound peace. The measurement of the pendulum was not forgotten. Borda, who had done so much to perfect all the other parts of the observations, invented for this experiment a method, the exactness of which surpassed every thing which had been till then imagined, and which has never been surpassed.

After these operations were terminated, it was thought that the arch of the meridian might be continued a good many degrees south, across Catalonia, and that it might even be possible to prolong it to the Balearic isles, by means of an immense triangle of which the sides extending over the sea, should join these isles to the coast of Valentia. Méchain devoted himself to this operation. I say that he devoted himself, for he died of fever in a small town

in the kingdom of Valentia, after having surveyed all the chain, and measured the first triangles. M. Arago and I were charged with the completion of the work, jointly with the commissioners of the king of Spain, Charles IV. We had the good fortune to succeed; but it is in remembrance, that M. Arago did not return to France without encountering great danger, and after a distressing captivity. Our results, by confirming those of the arc of France, gave them a new proof of accuracy. We measured also, at our most remote station, the length of the second's pendulum, after the method of Borda. M. Matthieu and I repeated the same operation upon different points of the arc comprised between Perpignan and Dunkirk. These experiments gave for the flattening of the earth, a value almost exactly equal to that which M. de Lambre had already obtained, by comparing the arc of France and Spain with the degree of the equator, calculated with new pains, and with the degree of Lapland which Mr. Swanberg, an able Swedish astronomer, had corrected by new observations; finally, with an arc of many degrees, which major Lambton had measured with great accuracy in the English possessions of India. Verified by so many combinations independent of each other, our arc of France and Spain acquired farther rights to become a fundamental model for measures. An occasion presented itself of making it of still more importance. Since the rebellion of 1745, the English government had perceived the utility of constructing a detailed map of the three kingdoms, which could serve equally to direct the amelioration of the country in time of peace, and its defence in time of war. I may state in passing, that it is the war which, for twenty years back, has given to geodesiacal operations the great extension, and the extreme perfection, which they have acquired in all the states of Europe; and the value of this slight advantage is thus enhanced by its being dearly enough paid for. However this may be, the English triangulation, begun by general Roy, and continued after him by colonel Mudge, was prolonged from the south of England to the north of Scotland, and presented in that extent many degrees of the terrestrial meridian, measured with excellent instruments. It was extremely desirable that this arc should be joined to the arc of France. But as, from the geographical position of England, she is placed a little to the westward of ours, there was ground to fear lest all the terrestrial mevidians, not being exactly alike, the difference of longitude would affect the results which might be obtained from that junction. Nevertheless, there could be no dread of this, so far as concerned the measurements of the pendulum, which are much less disturbed than the degrees by the slight irregularities of the figure of the earth. The Board of Longitude was desirous that the same apparatus which had served for these measurements in France and Spain, should be employed over the whole extent of the English. arc. To wish for any thing useful to the sciences, was to have at once the assent of the men of science in England, and the appro

bation of the government of that enlightened country. Neither the one nor the other was wanting to us. The respectable sir Joseph Banks, and his worthy friend sir Charles Blagden, assured us of all imaginable facilities. M. Lainé, the minister of the interior, with whom every thing useful or honourable has only possibility for its limit, was able, from the resources of his good will, to furnish means for this enterprise, and the Board of Longitude had the goodness to entrust me with the execution of it.

I left Paris at the commencement of the month of May, last year, carrying with me the apparatus I had made use of on the other points of the meridian, a repeating circle by M. Fortin, an astronomical clock, and chronometers by M. Breguet; in fine, every thing which was necessary for the observations. Orders from the English government, obtained through the vigilant intervention of sir Joseph Banks, awaited their arrival at Dover. The whole was sent to me quite entire, and under the seal of the customs, without fees, without inspection, absolutely as if I had not passed from one country to another. Every thing was protected with the same care in the carriage to London, and was at last deposited in the house of sir Joseph Banks. How can I describe what I felt on seeing for the first time the venerable companion of Cook, rendered illustrious by his long voyages, remarkable for a reach of mind, and an elevation of feeling, which make him equally interested in the progress of all human knowledge-possessing high rank, great fortune, and universal respect-sir Joseph has made all these advantages the patrimony of the learned of all nations. So simple, so easy in his kindness, it almost seems, to him who experiences it, the effect of a naturally acquired right; and at the same time he is so good, that he leaves us all the pleasure, all the individuality of gratitude. What a noble example of a protection whose sole authority is founded in esteem, respect, and free and voluntary confidence-whose titles consist only in an inexhaustible good will, and in the recollection of services rendered, and of which the long and uncontested possession necessarily supposes rare virtues, and an exquisite delicacy-when we reflect, that all this power is formed, maintained, and exercised among equals!

Under these honourable auspices, every thing became easy. Colonel Mudge, who had shown himself most favourably disposed towards our enterprise, seconded it by all the means in his power. We departed from Edinburgh together, and fixed our first station in the fort of Leith. There I received, equally from him and colonel Elphinston, commandant of the military engineers, all the assistance which the most eager wish to oblige could grant, or even suggest. I required a situation where the view was free, and which was at the same time sheltered, in order to erect my circle. I was induced to construct upon the terrace of the fort a portable observatory, which being capable of being easily taken to pieces at pleasure, permitted me to make observations on all sides