324 On ike Comparative Level of Lakes and Seas. 



a valuation which differed but little from that of Mayer. He assigns 10 

 toises for the difference of the level of the waters of the Volga and the 

 Don, at the place where the rivers most approximate. When to this we 

 add the 8 toises which M. Goebel found Zaritzin higher than the level of 

 the Caspian, by a very accurate barometrical levelling, we have for this 

 level — 18 toises. Nevertheless, we must remember that, according to a 

 geometric levelling recently made by the officers of the Imperial Corps of 

 Roads and Highways, the differences of the level of the Hon and Volga, 

 between Katchalinsk and Zaritzin, is twice as much as that stated above, 

 or 21.2 toises. MM. Parrot and Behagel have found it barometrically 

 to be 27 toises. From my own observation (on the 21st October 1829), I 

 found a difference somewhat less between the Volga and Tchivskaya upon 

 the Hon.* 



The barometrical means which the Acta Acad. Petrop, 1782, p. 24, sup- 

 ply for Astrakhan, Irkoutsk, Moscow, and St Petersburg, make the 

 Caspian — 45 toises. 



The astronomer WisnieiusH, from barometric observations of 3 years' 

 continuance, fixed the level at — 257 feet, or 42.8 toises. It is not, how- 

 ever, probable, that it was to this conclusion that Thomas Young refers, 1 

 where he affirms that the depression of the Caspian appears to be nearly 

 300 English feet (—47 toises). 



The barometric levelling by stations, executed in the year 1811, by 

 MM. Parrot and Engelhardt, between the Caspian and the Black Sea, gave 

 in going and returning, in 27 days, — 54.2 toises ; in 30 days, — 47.1 

 toises j mean, 50.6 toises. 



Monteith believed that he ascertained by the determination of the boil- 

 ing point of water, that the level was — 61 toises ; and Lohtiuj from baro- 

 metrical observations from 1806 to 1811, made at Astrakhan, that it was 

 — 39,toises4 



MM. Hofmann and Helmersen conducted with much care, in 1825, a 

 barometric levelling by stations from Orenbourg to Gourief, situated at 

 the embouchure of the Jaik (Oural) into the Caspian Sea. They found by 

 this levelling, and from corresponding barometric observations at the ex- 

 treme points, that Orenbourg was elevated 52 toises above the level of 

 the Caspian Sea. Now, M. Galle assigns from the whole barometric ob- 

 servations of MM. Hofmann and Karelin at Orenbourg, that this for- 

 tress is 39 toises above the ocean. From this it may be deduced, that 

 the Caspian has a depression of — 13 toises, a result which is remarkably 

 accurate, but which was for long misunderstood, because it was supposed 

 that Orenbourg stood but little above the level of the ocean. The baro- 

 metric observations which were made together by MM. Hofmann, Hel- 

 mersen, Rose, and myself, from the 12th to the 21st of October 1829 on the 



* Parrot, Reise zum Ararat, 1834, p. 13, 192. 



t Course of Lectures, 1807, vol. i. p, 571 ; vol. ii. p. 367. 



^ Paasner Hbhen im Europ. et Asiat. Russland, 1836, p. 23. 



