153 



point a, we have 11430 feet absolute height, or 1905 

 toises." 



The third measurement made by Mr. de Borda was a 

 barometrical one. We have extracted the following details 

 also from the Manuscript of the Depot, and find them 

 nearly agreeing with the results published by Mr. Cavanilles 

 in 1799, from the Manuscript of Don Jose Varela in the 

 Analts de Ciencias naturales *. " Mr. de Borda left Santa 

 Cruz the 27th of September 1776. He was accompanied by 

 forty persons, among whom were eleven officers of the 

 French and Spanish navy. They were provided with va- 

 riation compasses and dipping needles, a time-keeper, se- 

 veral thermometers, and two excellent barometers, which 

 had been compared, at the port of Orotava, with the baro- 

 meter of Mr. Pasley, a Scotch merchant +. On their return 

 from the Peak, these instruments were verified anew ; the 

 difference remained absolutely the same, and by the inter- 

 polation of a great nuim%r of observations made hourly by 

 Mr. Pasley, the following differences were found : 



must have subtended a vertical angle of 11° 29' 18". A slight 

 error appears in the altitudes of d above c, and of c above a. 

 At the port of Orotava, at the house of Mr. Cologan, the 

 apparent altitude of the volcano was found to be 11° 29' 35". 

 An azimuth gave for the position South 29° 44' west, 

 whence results a distance of 0° 9' 45". 



* T. i, p. 295. I know not from what misunderstanding 

 it is asserted, in this same work (t. i, p. 85), that 1 had 

 found the height of the Peak 1917 toises. 



f Mr. Pasley declared, that he had not observed, for seve- 

 ral years, Reaumur's thermometer at the port of Orotava, 

 above 22*7°, or below 12' 5°. 



