I had scarcely entered the Observatory, when I became the fellow-labourer of Biot in researches on the refraction of gases, already commenced by Borda.

While engaged in this work the celebrated academician and I often conversed on the interest there would be in resuming in Spain the measurement interrupted by the death of Mechain.  We submitted our project to Laplace, who received it with ardour, procured the necessary funds, and the Government confided to us two this important mission.

M. Biot, I, and the Spanish commissary Rodriguez departed from Paris in the commencement of 1806.  We visited, on our way, the stations indicated by Mechain; we made some important modifications in the projected triangulation, and at once commenced operations.

An inaccurate direction given to the reflectors established at Iviza, on the mountain Campvey, rendered the observations made on the continent extremely difficult.  The light of the signal of Campvey was very rarely seen, and I was, during six months, in the Desierto de las Palmas, without being able to see it, whilst at a later period the light established at the Desierto, but well directed, was seen every evening from Campvey.  It will easily be imagined what must be the ennui experienced by a young and active astronomer, confined to an elevated peak, having for his walk only a space of twenty square metres, and for diversion only the conversation of two Carthusians, whose convent was situated at the foot of the mountain, and who came in secret, infringing the rule of their order.

At the time when I write these lines, old and infirm, my legs scarcely able to sustain me, my thoughts revert involuntarily to that epoch of my life when, young and vigorous, I bore the greatest fatigues, and walked day and night, in the mountainous countries which separate the kingdoms of Valencia and Catalonia from the kingdom of Aragon, in order to reestablish our geodesic signals which the storms had overset.

I was at Valencia towards the middle of October, 1806.  One morning early the French consul entered my room quite alarmed:  “Here is sad news,” said M. Lanusse to me; “make preparations for your departure; the whole town is in agitation; a declaration of war against France has just been published; it appears that we have experienced a great disaster in Prussia.  The Queen, we are assured, has put herself at the head of the cavalry and of the royal guard; a part of the French army has been cut to pieces; the rest is completely routed.  Our lives would not be in safety if we remained here; the French ambassador at Madrid will inform me as soon as an American vessel now at anchor in the ‘Grao’ of Valencia can take us on board, and I will let you know as soon as the moment is come.”  This moment never came; for a few days afterwards the false news, which one must suppose had dictated the proclamation of the Prince of the Peace, was replaced by the bulletin of the battle of Jena.  People who at first played the braggart and threatened to root us out, suddenly became disgracefully cast down; we could walk in the town, holding up our heads, without fear henceforth of being insulted.