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 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 for- 

 mulae, when I was, by order of the Bureau of Longitude, 

 obliged to leave Paris for Spain. I had observed vari- 



