regained courage, especially on considering that the three last years of
my life had been consecrated to the measurement of an arc of the
meridian in a foreign country; that they were passed amid the storms of
the war with Spain; often enough in dungeons, or, what was yet worse, in
the mountains of Kabylia, and at Algiers, at that time a very dangerous
residence.

Here is, therefore, my statement of accounts for that epoch. I make it
over to the impartial appreciation of the reader.

On leaving the Polytechnic School, I had made, in conjunction with M.
Biot, an extensive and very minute research on the determination of the
coefficient of the tables of atmospheric refraction.

We had also measured the refraction of different gases, which, up to
that time, had not been attempted.

A determination, more exact than had been previously obtained, of the
relation of the weight of air to the weight of mercury, had furnished a
direct value of the coefficient of the barometrical formula which served
for the calculation of the heights.

I had contributed, in a regular and very assiduous manner, during nearly
two years, to the observations which were made day and night with the
transit telescope and with the mural quadrant at the Paris Observatory.

I had undertaken, in conjunction with M. Bouvard, the observations
relating to the verification of the laws of the moon's libration. All
the calculations were prepared; it only remained for me to put the
numbers into the formulæ, when I was, by order of the Bureau of