terials yet exist for so important a work. 
Without the aid of geodesical instruments^ 
by which we measure very small angles, it 
is almost impossible to determine the outlines 
with sufficient exactness. While I was em- 
ployed in these measurements in the southern 
hemisphere, on the ridge of the Cordilleras 
of the Andes, Mr. Osterwald, with the assis- 
tance of a celebrated astronomer, Mr. Tralles, 
was sketching, by a similar method, the chain 
of the Alps of Switzerland, as it appears when 
viewed from the banks of the lake of Neuf- 
chatel. This view, lately published, is so very 
exact, that, the distance of each summit being 
known, their relative height is found by em- 
ploying in the calculation only the simple mea- 
sure of the outlines of the drawing. Mr. Tralles 
made use of a repeating circle. The angles by 
which I determined the size of the different 
parts of the mountain were taken with a sextant 
by Ramsden, the limb of which marked with 
certainty six or eight seconds. By the repetition 
of this operation at the interval of distant pe- 
riods, the accidental changes, which take place 
on the surface of the Globe, may some day be 
verified. In a country exposed to earthqukes, 
and overwhelmed by volcanoes, it is very diffi- 
cult to determine whether the mountains dimi- 
nish, or whether by the ejection of ashes and 
scoriae they insensibly augment. The simple 
