Level of the Black Sea and the Caspian, lib 



a little to the north of the mouth of the Terek, where the 

 operations were terminated. The whole extent of this line is 

 about 800 versts (about 600 English miles). 



The measurements were of two kinds, — Trigonometrical 

 and Barometrical; and the following are the results obtained : — 



Height of the Sea of Azov above the Caspian. 



Calculated by M. G. Fuss {^BulL Scient. de I'Acad. de St Petersh., 1838, 

 vol. iv. p. 241.) 



According to the method of simultaneous^ reciprocal. Zenith-dis- 

 tances, .... 73.1 feet English. 

 According to the method of the mean of the Zenith- 

 ES5 distances, .... 76.2 

 Calculated by M. Sawitsch (in his Dissertation, 1839, p. 22.) 

 According to the method of simultaneous, reciprocal, Zenith-dis- 

 tances, .... 78.1 feet English. 

 (Probable error =: 3.6 feet.) 

 According to the method of the mean of the Zenith- 

 distances, . , . 82.6 

 (Probable error = 6.2 feet.) 



Calculated by M. Sadler (in his Dissertation, 1839, p. 33.) 

 According to the method of simultaneous, reciprocal Zenith-dis- 

 tances, .... 83.3 feet English. 

 (Probable error = 2.4 feet.) 

 According to the method of the mean of the Zenith- 

 distances, . . . 81.3 

 (Probable error := 3.9 feet.) 



The discrepancies in these results arise from the way in which 

 the observers have calculated the measurements for the pur- 

 pose of removing the effect of terrestrial refraction. We can- 

 not decide as to which of these results is most probably the 

 correct one ; but it is evident that, as the uncertainty amounts 

 only to a few feet, we shall not be very far wrong in assuming, 

 as the number most nearly approaching the truth, the mean 

 of the four last (which are those that agree the best with one 

 another), viz., 81.3 English feet. Even should this number 



there is an intervening piece of extremely flat ground, three or four versts in 

 breadth (two or three miles English). When, likewise, they reached the 

 point forming the water-shed of the two seas, they were struck by the dif- 

 ferent aspect of the surface of the country presented to them. The tract is 

 doubtless the former bottom of the Caspian. 



VOL. XXIX. NO. LVII.— JULY 1840. K 



