The _Dépôt de la guerre_, however, would have attained but imperfectly the object of its institution, had there not been added to its topographical treasure, the richest, as well as the finest, collection in Europe of every geographical work held in any estimation. The first epochs of the revolution greatly facilitated the increase of its riches of that description. The general impulse, imprinted on the mind of the French nation, prompted every will towards useful sacrifices. Private cabinets in possession of the scarcest maps, gave them up to the government, The suppression of the monasteries and abbeys caused to flow to the centre the geographical riches which they preserved in an obscurity hurtful to the progress of that important science: and thus the _Dépôt de la guerre_ obtained one of the richest collections in Europe.[3] The government, besides, completed it by the delivery of the great map of France by CASSINI, begun in 1750, together with all the materials forming the elements of that grand work. It is painful to add that not long before that period (in 1791) the corps of geographical engineers, which alone could give utility to such valuable materials had been suppressed.[4] In the mean time, the sudden changes in the administrative system had dispersed the learned societies employed in astronomy, or the mathematical sciences. The _National Observatory_ was disused. The celebrated astronomers attached to it had no rallying point: they could not devote themselves to their labours but amidst the greatest difficulties; the salary allowed to them was not paid; the numerous observations, continued for two centuries, were on the point of being interrupted. The _Dépôt de la guerre_ then became the asylum of those estimable men. This establishment excited and obtained the reverification of the measure of an arc of the meridian, in order to serve as a basis for the uniformity of the weights and measures which the government wished to establish. MÉCHAIN, DELAMBRE, NOUET, TRANCHOT, and PERNY were dispatched to different places from Barcelona to Dunkirk. After having established at each extremity of this line a base, measured with the greatest exactness, they were afterwards to advance their triangles, in order to ascend to the middle point of the line. This operation, which has served for rectifying a few errors that the want of perfection in the instruments had occasioned to be introduced into the measure of the meridian of CASSINI, may be reckoned one of the most celebrated works which have distinguished the close of the eighteenth century.