Imperial Academy of Sciences of St Petersburg. 109 



and upon the pupils of that excellent institution, the School of 

 Canals, Bridges, and Roads, in which mathematical studies of a 

 \\\o\\ order cive rise to a kind of instinctive taste for order and 

 precision. 



Along with the two objects of research which we have just 

 examined in their relation to the extent of the empire (the earth's 

 magnetism and the study of the atmosphere, which leads at the 

 same time, by the aid of the mean heights of the barometer, to 

 the improved knowledge of the configuration of the ground), I 

 would mention, in concluding, a third kind of inquiry of a more 

 local interest, although connected with the great questions of 

 physical geography. A considerable part of the earth's surface 

 around the Caspian Sea, is inferior to the level of the Black Sea 

 and the Baltic. This depression, which had been supposed for 

 more than a century, and which has been measured by the 

 laborious efforts of MM. Parrot and Engelhardt, may be 

 ranked among the most surprising geognostical phenomena. 

 The exact determination of the mean annual barometric height 

 of the city of Orenburg, which we owe to MM. Hoffmann and 

 Helmerssen; a levelling (nivellement par station ?) made by 

 the aid of the barometer, by the same observers, from Orenburg 

 to Gourief, the eastern port of the Caspian Sea ; corresponding 

 measures taken during several months in these two places ; and, 

 lastly, observations recendy made by us at Astracan and at the 

 mouth of the Volga, corresponding at once to Sarepta, Orenburg, 

 Cazan, and Moscow, will serve, when all the data are brought 

 together and rigorously calculated, to verify the absolute height 

 of this internal basin. 



On the northern side of the Caspian Sea, every thing appears 

 to indicate at the present day a progressive diminution of the 

 level of the waters ; but without giving too much credit to the 

 report of Hanway (an old English traveller, of otherwise re- 

 spectable character), about the periodical risings and fallings, we 

 cannot deny the encroachments of the Caspian Sea near the an- 

 cient city of Terek (perhaps the old town of Terek or Old Terek) 

 and to the south of the mouth of the Cyrus, where scattered 

 trunks of trees, the remains of a forest, are seen always inun- 

 dated. The islet of Pogorelaia Plita, on the contrary, seems to 

 be progressively extending and rising above the waves, which, 



