nal 
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80 AUTOBIOGRAPHY OF FRANCIS ARAGO. 
considerable, if estimated in an absolute manner; but 
when I judged by comparison, I regained courage, espe- 
cially on considering that the three last years of my life 
had been consecrated to the measurement of an are 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 for- 
mule, when I was, by order of the Bureau of Longitude, 
obliged to leave Paris for Spain. I had observed vari- 
