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 ; 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 ; heights of the barometer Without any notice 

 taken of the temperature of the air and of the mercury j 

 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 



JLamanon, 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 ; 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- 



