150 



KNOWLEDGE, 



[June 1, 1897. 



we shall never kuow how many shipwrecks may have been 

 due to this error. Even mora important, from the 

 scientific point of view, was the fact that Picard'a new 



'I'riangulation uear the Kirer Danube. 



measurement furnished Newton with the long-desired 

 confirmation of the law of gravitation. 



The idea of a Kussiau meridian arc had its birth in the 

 iirst half of the last century, when the Paris Academy of 

 Sciences was so hotly discussing the figure of the earth as 

 derived from the discordant results of different geometers. 

 Delisle, indeed, actually commenced operations in 1737, 

 but, for reasons not sufficiently known, his project was 

 abandoned. 



In 1812, while still a student at the University of 

 Dorpat, Struve was struck by the great advantages which 

 the region between the Danube and the Arctic Ocean 

 offered for a trigonometrical survey. A stretch of country 

 almost free from high mountains, the astronomical obser- 

 vations would be correspondingly little distiu-bed by local 

 attractions. In the summer of 1812, Struve, single- 

 handed, made a small survey, measuring a base line, and 

 carrying on a triangulation with a Troughton sextant. 

 His work, however, was interrupted by war, but it sufficed 

 to show the feasibility of a greater undertaking. After his 

 appointment to the observatory of Dorpat, Struve's projects 

 received official recognition, and the Emperor Alexander I. 

 granted the funds necessary to complete the measurement 

 of an arc of 3" 35'. This was concluded in 1828, and was 

 subsequently joined to an arc which had been almost 

 simultaneously measured by General Tenner. The j unction 

 between the two surveys was made in 1831, the total arc 

 then amounting to 8^ 2-5', between Hogland and Belin. 

 A lacuna of 5° 2G' between this Russian arc and the 

 Lapland arc previously measured by the French and 

 Swedes was next attacked, the Emperor Nicholas I. 



cordially supporting the work by an annual grant of three 

 thousand roubles for ten years. It was not until 1841, 

 however, that this portion of the great arc. terminating at 

 Tornea, latitude G5^ 50', was completed. During the next 

 seven years the arc was extended to Staro-Nekrassowka, 

 on the Danube, in a southerly direction, by General 

 Tenner, and to Fuglenaes, Hammerfest, towards the 

 north, by the Norwegians and Swedes. 



With due respect for the historic rights of the Academy 

 of Stockholm, M. Struve was deputed to impress on that 

 body the importance of extending the Russian are to the 

 northern extremity of the continent, and a personal inter- 

 view with the King. Oscar I., led to the desired object. 

 Reconnoitring expeditions were first sent out, stations 

 were selected, and Hammerfest, for various practical 

 reasons, was determined upon as the extreme end of the 

 arc. Surveying in these liigh latitudes is beset with many 

 dilficulties. Owing tn tlie mountainous character of the 

 country, transport is difficult, while inhabitants are few 

 and wood is scarce. Hammerfest, for instance, is pardon- 

 ably proud of a scraggy clump of dwarf birch, a score or 

 two in number, for this is the nearest approach to a 

 wood within many miles radius. 



Near the southern limit of the arc, excessive vegetation, 

 in the shape of almost impenetrable forests, presented 

 great obstacles, and observing platforms and signals nearly 

 one hundred and fifty feet in height bad sometimes to be 

 erected. 



Finally, after nearly forty years' labours, the measure- 

 ment of the great arc was accomplished. Altogether ten 

 bases were measured and two hundred and fifty-eight 

 principal triangles were involved. From end to end the 

 meridian arc traverses no less than two thousand eight 

 hundred and eighty kilometres, embracing about one- 

 fourteenth of the earth's circumference. 



The southern termination, at Staro-Nekrassowka, latitude 

 45° 20' 2-8", is marked by a truncated pyramid of cast 

 iron, resting on a cube of seven feet side, bearing an 

 inscription almost identical with that of the Hammerfest 

 monument. 



Combining the results of the Russian arc of meridian 

 with the Anglo-French, Indian, Cape, and Peruvian arcs, 

 and an Indian arc of longitude (giving a total amplitude of 

 89° 32'), and regarding the shape as spheroidal, General 

 Clarke determined the following values for the size of the 

 earth : — 



Equatorial diameter = 41,852,401 feet. 

 Polar diameter = 41,709,790 feet. 



While there is reason to believe that an equatorial 

 section of the earth should be regarded as an ellipse — in 

 other words, that the earth is an ellipsoid — it is not yet 

 considered by the best authorities that the available data 

 are sufficient for fixing definitively the form and dimensions 

 of the imaginary geometrical smooth body which most 

 nearly approximates to the actual contour of the earth's 

 surface. 



As Struve pointed out at the conclusion of his labours, 

 nature presents no obstacle to the southern extension of 

 the great arc by another 12 ' ; and, more recently. Dr. G'iW 

 has looked forward to its connection with the South 

 African survey which has just been completed. Dr. Gill 

 considers that the Soutti African triangulation might be 

 extended to the mouth of the Nile, and then, by an 

 additional network of triangles along the coast of the 

 Levant and through Greece, the junction with Struve's 

 meridian could be made so as to produce a stupendous arc 

 of 105\ Many years must elapse before such an enormous 

 undertaking can bo completed, but its importance as a 

 contribution to exact geodesy cannot be over-estimated. 



