HISTORY OF GEODETIC OPERATIONS IN RUSSIA. 307 



The angles in this net were measured with repeating circles, employing 

 for each angle from twenty to fifty repetitions. For the probable error 

 of angle determinations 0".62 was found to be an average. Astronomic 

 observations were made at only one point with the longitudes referred 

 to the observatory of Vilna. 



AlQiost simultaneously' with the above-named operations in Vilna, a 

 young enthusiastic astronomer of the Dorpat University, W. Struve, 

 acting in response to a request from the Livonian Economical Society, 

 covered Livonia with a trigonometrical net. In this work the angles 

 were measured with a sextant and the bases with wooden rods, so that 

 but little confidence can be placed in the results, still it was while en- 

 gaged upon this work that Struve formed a liking for geodesy and con- 

 ceived the plan of making a great arc measurement for the purpose of 

 determining the lengths of degrees in different latitudes. 



His great interest in the work attracted the attention of the univer- 

 sity authorities, and in answer to his request they furnished him with 

 the necessary means and instruments. The base apparatus was of his 

 own invention, and still bears his name. The salient feature intro- 

 duced in its construction was the contact lever, which indicated on a 

 graduated arc over which one end of the lever swept the exact measur- 

 ing length each time the bar was put in place. Inclination was deter- 

 mined by means of a special level. 



A large theodolite, provided with four verniers, served as the angle- 

 reading instrument. In this work Struve was the first to abandon the 

 seductive, unreliable method of repetition, using in its place the method 

 of directions. It was so apparent to many that an angle measured say 

 twenty times, with only one reading of the circle, would be affected by 

 an error only one-twentieth as large as if the single reading corre- 

 sponded to only one pointing. Struve clearly saw that this method 

 introduced other errors more pernicious than those of reading, but so 

 firndy was the Borda repeating circle fixed in the confidence of its 

 users that had not Gauss embraced the new plan in his monumental 

 work it is likely that the method of repetition would have continued 

 to impair geodetic determinations. However much we are indebted to 

 Gauss for assisting in the change, we owe the inception to Struve. 



The results of this first degree measurement, which extended from the 

 isle of Hohland, in the Finnish Gulf, to the town Jacobstadt, on the river 

 Dvina, are given in Struve's Breitengradmessung in den Ostseeprovinsen 

 RmdandSj Dorpat, 1831. 



On finishing this work, Struve, seeing no natural obstacles in the 

 way, hoped to extend an arc along the meridian of Dorpat. He was 

 soon in a i)osition to take up this undertaking, since as director of the 

 observatory at Pulkova he was virtually at the head of all astronomic 

 and geodetic operations in Russia. Fortunately he received tlie appro- 

 bation of Emperor Nicholas, and under his patronage this branch of 

 scientific work prospered. The great arc, which received well-nigh 

 uninterrupted attention for more than 40 years, had as its central fea- 



