DON FELIX D'AZARA. 27 



telescopes of Halley, and an artificial horizon. Wher- 

 ever I was, even in the camp, I took the latitude 

 every day at noon, and every night, by means of 

 the sun and stars. My compass was furnished with 

 sights, and I often verified the variation by compar- 

 ing the azimuth with the results of my calculations 

 and solar observations. To render my chart more 

 exact, and to adjust the meridians to that of Paris ; 

 I made many observations of the immersion and 

 emersion of Jupiter's satellites, of solar eclipses, 

 and of the occultation of the stars by the moon, at 

 Monte Video, Buenos Ayres, Corrientes, and As- 

 sumption, and it was according to these results that 

 I fixed my degrees of longitude." 



The extent of these surveys was prodigious. In 

 regard to the geographical investigations, on which 

 we are now more especially dwelling, they ex- 

 tended, as already mentioned, to about fifteen hun- 

 dred miles by nine hundred; and in respect to 

 some other of his inquiries, they reached over a 

 much wider range. In his chapter on climate, he 

 remarks, " These limits include a very irregular 

 surface, whose geographic limit alone extends seven 

 hundred and twenty leagues, with a mean breadth 

 of two hundred, an extent nearly equal to the whole 

 of Europe. I have not myself traversed the whole 

 of this last space, but the information I have pro- 

 cured may be depended on/' We are not, however, 

 to contemplate him as working single-handed. His 

 rank and appointments enabled him to avail himself 

 of the services of many associates and officers of in- 



