144 COSMOS. 



In order to follow the usual direction of Siberian expedi- 

 tions from west to east, and starting from Europe, we will 

 begin with the northern part of the Caspian Sea. Here, in 

 the small island of Birutschikassa, in Astracan, on Lake El- 

 ton, in the Kirghis steppe, and at Uralsk, on the Jaik, be- 

 tween 45 43' and 51 12' N. lat., and 40 37' and 51 24' 

 E. long., the variation fluctuates from 10' east to 37 ' 

 west.* Farther northward, this line of no variation inclines 

 somewhat more toward the northwest, passing near Nishnei- 

 Novgorod.f In the year 1828 it passed between Osablikowo 

 and Doskino in the parallel of 56 N. lat. and 43 east long. 

 It becomes elongated in the direction of Russian Lapland be- 

 tween Archangel and Kola, or more accurately, according to 

 Hansteen (1830), between Umba and Ponoi.f It is not un- 

 til we have passed over nearly two thirds of the greatest 

 breadth of Northern Asia, advancing eastward to the lati- 

 tudes of from 50 and 60 (a district in which at present the 

 variation is entirely easterly), that we reach the line of no 

 variation, which in the northeastern part of the Lake of Bai- 

 kal rises to a point west of Wiluisk, which reaches the lati- 



of the portions of the moon visible to us. In a letter addressed to the 

 czar, discovered by Pertz, Leibnitz describes a small hand-globe, or 

 terrella, which is still preserved at Hanover, and on which he had rep- 

 resented the curve at which the variation is null (his lima magnetica 

 j>riinaria). Leibnitz maintains that there is only one line of no varia- 

 tion, which divides the terrestrial sphere into two almost eqnnl parts, 

 and has four pimcta jlexus contrarii, or sinuosities, where the curves 

 are changed from convex to concave. From the Capo do Verd it 

 passes in lat. 36 toward the eastern shores of North America, after 

 which it directs its course through the South Pacific to Eastern Asia 

 and New Holland. This line is a closed one, and, passing near both 

 poles, it approaches closer to the southern than the northern pole; at 

 the latter the declination must be 25 west, and at the former only 

 5. The motion of this important curve must have been directed to- 

 ward the north pole at the beginning of the 18th century. The varia- 

 tion must have ranged between and 15 cast over a great portion 

 of the Atlantic Ocean, the whole of the Pacific, Japan, a part of 

 China, and New Holland. "As the czar's private physician, Donelli, 

 is dead, it would be advisable to supply his place by some one else, 

 who will be disposed to administer very little medicine, but who may 

 be able to give sound scientific advice regarding determinations of 

 magnetic declination and inclination." These hitherto un- 

 noticed letters of Leibnitz certainly do not express any special theo- 

 retical views. 



* See my Magnetic Observations, in Asie Centrafa, t. iii., p. 460. 



f Erman, Astron. und Magnet. Bcobachlungcn (Rdsc nm die JErde, 

 abth. ii., bd. 2, s. 532. 



J Hansteen, in Poggend., Ann., bd. xxi., s. 371. 



