180 Scientific Intelligence — Hydrography. 



equatorial to that of our own day ; it is easy to determine the 

 difference. Natural philosophers, by resting on their beautiful 

 theories of heat, have doubtless been able to suppose a priori 

 the changes of temperature of which I have spoken ; it is, never- 

 theless, curious to perceive their conjectures confirmed by a 

 science for a long time neglected, and which no one thought of 

 directing to this new object."*" 



HYDROGRAPHY. 



9. The Level of the Caspian much below that of the Ocean.^^ 

 In 1814, Messrs Engelhardt and Parrot attempted to determine, 

 by means of the barometer, if, as was long ago supposed, the wa- 

 ters of the Caspian Sea are less elevated than those of the Medi- 

 terranean and the ocean. The mean of three determinations 

 gave a difference in this respect of 98 metres. But subsequently 

 M. Parrot having thrown some doubt on the result of these ob- 

 servations, made in 1814, M. Erman has taken up the subject, 

 and the following is the result of his investigations : Barometri- 

 cal observations made for seven years at Kasan, compared with 

 corresponding observations made during the same period at Dant- 

 zig, give 31.8 metres as the height of the former town above 

 the level of the Baltic. This result is confirmed by six years' 

 observations at Mitau. Hence, with the assistance of levelling, 

 M. Erman concludes that the height of the junction of the Ka- 

 sanka with the Volga, is only 8.8 metres above the Baltic. 

 Thus, in order that there should be a coincidence between the 

 levels of the Caspian and the Baltic, it would be necessary that, 

 in the extent of 205 German miles between Kasan and Astracan, 

 the descent of the river should not be more than 8.8 metres, 

 which seems inadmissible. The descent of the Volga from Tor- 

 jok to Kasan, in an extent of 155 miles, has been measured. 

 Supposing that, in the remainder of its course, the river follows 

 the same law, M. Erman has ascertained that the depression of 

 the Caspian Sea, compared with the Baltic, would be eighty- 

 four metres — a result which does not differ much from that 

 (ninety-eight metres) obtained by Messrs Engelhardt and Parrot. 

 10. Spring at the Summit of a Mountain. — M. Durieu, who 

 lately made a scientific journey in the kingdom of the Asturias, 

 mentions the following important fact in physical geography :^ 



