J 6 Dr. Kirivan on the primiti've State of ih£ Glohc. 



generally known * before Mr. De Luc's immortal work on 

 the modifications of the atmofphere, which was not pub- 

 liiliod till upwards of thirty years after Don Ulloa's experi- 

 ments. The air, then, remaining in his barometer, which 

 lie probably filled at Lima, iu whofe territory Guancavelica 

 lie?, under a prelliire of 28 or between 27 and 28 (French) 

 inches, muft have confiderably expanded and deprefTed the 

 columiT of mercury under it when brought up a mountain of, 

 perhaps, 7000 or 8oco feet high ; and hence this mercurial 

 column remained fo low at Guancavelica as eighteen inches 

 and one line. 



That in thcfe circumftances the air contained in the baro- 

 meter might caufe a difference of three inches or more be- 

 tween the hcioht at which mercury purged of air would 

 Hand, appears hv the experiments of Caflfini, Mem. Par. 

 1740, fur la JSleriiiiimnc de Paris, p. 172 ; for he found that 

 the mercury, freed from air by ebullition in the tube, (tood 

 four or five lines higher than in barometers filled without 

 that precaution. Nay, cardinal Luynes found the difference 

 betwixt fuch barometers to amount fometimes to fourteen 

 Tines; ]Mem. Par. 1768, p. 490, in 8vo. How great muft 

 it therefore be in barometers tranfported lo greater heights 

 than that at which they were filled r 



Moreover, Don TJlloa exprcfsly tells us that the mountain 

 on which thefe fhclls were found was every where habitable^ 

 Mim. Phikjbpbrques, p. 34 and 35 ; which it could not be, 

 and would be exprei^ly contradifted by Bouguer, if its height 

 u'crQ 13,000 Englifii feet over the furface of the fea. From 

 all which I conclude that the height of the mercurial column, 

 if the barometers had been properly conftru6ted, would have 

 been about 22 French inches, -- 23,44 Englifh ; and, as the 

 temperature was remarkably cold, this would indicate a height 

 of about 8200 feet above the level of the fea. 



But, fecondly, let the height be what it may, it is certain 

 that thefe fliells were depofited there after the emerfion of 

 land from the primitive ocean, and confequently by a fub- 

 fequent delude ; for Don TJlloa exprefsly tells uS, that in the, 

 fame rocks in which thefe (hells are found, peh-'ified wood is 

 alfo founds Mem. Philofophiques, p. 372. This wood muft 

 have grown on dry land, and muft have been floated when 



' I fay, not generally known, becaufe, though Mr. Du Fay had Ihown 

 the advantage of expelling air from the mercury in the tube, in Mem. Par. 

 1723, and Ca'.fini had followed that method in mcafuring the heights of 

 I'uv de Dome and Mont d'Or in 1740, yet it was not generally adopted 

 until Mr. De Luc had proved its necellity, and perfected- the method of 

 pcfforminij it, m 1772. bee De Luc, i. p. 5S. 



the 



