312 HISTORY OF GEODETIC OPERATIONS IN RUSSIA. 



points from Moscow to Vladivostak, coveriDg Siberia and embracing 

 arcs having a total amplitude of more than 100°. This huge undertak- 

 ing had two objects in view: to give the exact position of a number of 

 stations which were to serve as the bases of numerous smaller opera- 

 tions, especially chrouometric expeditions, and to determine in the 

 most accurate raaner the longitude of stations where observations of 

 the transit of Venus were to be made in 1874. The observations were 

 made with portable transit instruments specially adapted for quick and 

 convenient shifting in azimuth, making it i)ossibl6 to readily place the 

 instrument in the vertical of Polaris. For latitudes these same instru- 

 ments were used, being placed in the prime vertical. The account of 

 this expedition takes u}) nearly the whole of the thirty-eighth volume 

 of the Memoirs of the Topographical Section of the General Staff. 

 Upon examination it is found that the latitudes were affected with a 

 probable error of 0".l, while the probable error of a longitude deter- 

 mination is 0".043. From the successive transmission of time back- 

 wards and forwards the velocity of the galvanic current was found to be 

 93,548 kilometres per second. 



While the triangulation was in progress, zenith-distances were ob- 

 served from which the heights of stations were completed, but these 

 operations have not been consistently followed out, so that there are 

 in many parts of Russia a lack of well-determined altitudes. General 

 Tenner gave due attention to this special werk, and in his chain he 

 united the Baltic and the Black Seas. His results showed that the 

 former is 0.53 fathom higher, but as the probable error is 1.5 fathoms 

 but little confidence was placed in the theory that there was any differ- 

 ence in the level of these two seas. But with the Caspian Sea a dif- 

 ferent state of affairs was supposed to exist. It had been suspected 

 that this sea was lower than either of the two just named, so in 1836-'37, 

 a large expedition was organized, in which Fuss, Sawitch, and Sabler 

 were participants. They began at Kagalnik near the Asov Sea, crossed 

 the northern portion of the Caucasian deserts to the Tschornoi Eynok 

 on the Caspian. For greater accuracy the zenith distances were meas- 

 ured at very short distances, approsim ately 3.5 versts. These distances 

 were ascertained by computation from short lines measured by placing"' 

 bars end to end on a rope stretched tight. The results, published in 

 1849, showed that the Casj^ian Sea is 85.45 feet lower than the Black 

 Sea. Subsequently almost the same value was obtained, but still later 

 a value 4 feet greater was found, suggesting that the level of the Cas- 

 pian is decreasing. This fact has had further demonstration. The 

 academician Leuz made a mark on a rock near the town of Baku ex- 

 actly on a level with the sea; this mark in 18G1 was 3,93 feet higher 

 than the water, and more recent comiiarisons show that the difference 

 is increasing. 



The other Russian interior sea, the Aral, is, on the contrary, higher 

 than the level of the ocean. The special levelling party sent out for 



