160 



other, than those which were found by the barometer. It 

 has nevertheless been extremely wrong to cite this want of 

 harmony as a proof of the uncertainty of all measurements 

 of mountains. Angles, the value of which is determined by 

 imperfect graphometers j bases that have not been levelled, 

 or the length of which has been determined by the log ; 

 triangles that give an excessively acute angle at the summit 

 of the mountain j heights of the barometer without any notice 

 taken of the temperature of the air and of the mercury ; 

 unquestionably are not means calculated to lead to accurate 

 results. Of fourteen trigonometrical and barometrical ope- 

 rations above indicated, the four following only can be con- 

 sidered as true measurements. 



toises. 



Borda by trigonometry . . . . 1905 



Borda by means of the barometer . . 1976 



Lamanon, the same . . . . 1902 



Cordier, the same . . . . 1920 



The average of these four observations, the whole of the 

 particulars of which are known to us, makes the absolute 

 height of the Volcano 1926 toises j but we must here discuss 

 the question, whether, in taking the mean, we ought to ex- 

 clude Borda's barometric measurement, as erring too much in 

 excess j or whether we ought not prefer the result of the tri- 

 gonometrical to that of the barometric measurements of a peak 

 almost continually swept by ascending or descending winds. 



The trigonometrical operation, made in 1776, is more 

 complicated than those generally are, by which we determine 

 the elevation of a single point. Travellers are in the prac- 

 tice of employing either a base directed toward the summit 

 of a mountain, and two vertical angles taken at the extremi- 

 ty of this base, or rather a base nearly perpendicular to the 

 former, two angles of position taken in an oblique plane, and 

 a single vertical angle. In both cases a direct measure is 

 taken of a side of the triangle, the summit of which is at the 

 top of the mountain. The measurement of the Peak exe- 



