On the Comparative Level of Lakes and Seas. 325 



shores of the Caspian, were 'compared with corresponding observations 

 at Kasan ; and they have made us sceptical ever since respecting any 

 very great depression of the Caspian. 



M. Parrot, whose premature loss science has to regret, during his me- 

 morable journey to Ararat, conceived doubts concerning the accuracy of 

 two barometric Icvellings by stations which he had executed with extreme 

 care, though labouring under fever, in the year 1811. In 1830, he had 

 the energy to repeat this painful labour between Astrakhan and New 

 Tcherkask, which occupied him for twelve days. From these observa- 

 tions, he concluded, that there exists only a slight difference in the level 

 of the surfaces of the water of the Black Sea and the Caspian.* It would 

 not be easy sufficiently to commend the stem and noble candour which 

 M. Parrot has displayed in discussing his own barometrical observations. 

 The source of error ought to be sought for alone in the barometric me- 

 thod of levelling by stations, to which the mode of observations made at 

 the extremities of a geodcesical line is greatly preferable. In the partial 

 levelling by stations, the errors accumulate by the influence of the frequent 

 change of local temperature, and by the comparison of two instruments, 

 the one of which, and the same one, always preceding the other. Another 

 barometric levelling by stations was likewise executed in the years 1838 

 and 1839, simultaneously with the geodsosical levelling by M. Fuss. By 

 various accidental causes it again yielded a result of— 47 toises, a depres- 

 sion almost identical with that given by the first operation by stations, 

 in 1811, by M. Parrot. 



The results derived from the barometric observations taken on the 

 shores of the Caspian and Black Seas have been very different, M. Sa- 

 witsch, from observations made at Taganrog and at Astrakhan, has made 

 the depression — 22.2 toises ; M. Gbbelt from observations at Astrakhan 

 and Sympheropol, has made it .15.9 toises; and M. Lenz, by comparing 

 3510 barometric observations made in 1830 at Bakou by M. Meyer, and 

 at Taganrog by M. Meyer, 16.8 toises. | 



If, thanks to the admirable labours of MM. Fuss, Sabler, and Sawitsch, 

 we now know with mathematical precision the real depression of the level 

 of the Caspian Sea, amounting to 12.7 toises, the accounts of the height 

 between the Caspian and the Lake Aral are not equally certain. These 

 accounts have been tiiken only by means of barometric levelling by stations 

 conducted during the military expedition of rOust-Ourt,§ during the 



* See Jicise nach dem Ararat, T. ii. p. 12-31 ; likewise Letter of M. do 

 Humboldt, of date 28th May 1834, stating doubts of a depression of 200 or 300 

 feet attributed to the basin of the Caspian Sea. T. ii., p. 101-198. 



I M. Gobel has compared the barometric observations of M. Offe at Astrakhan, 

 those of M. Steven at Sympheropol, and his own at the Sea of Azov. Gobel, 

 Reise, T. ii. p. 103. 



J Recueil des Actes de I'Acad. de St Petersburg, 1836, p. 20. 



§ See T. i. p. 421. The direct result obtained by MM. Sagoskin, Anjou, and 



