HISTORY OF GEODETIC OPERATIONS IN RUSSIA. 311 



allel, but also for locating or correcting the location of points distant 

 from fixed observatories, was it early necessary to ascertain differences 

 of longitude. The first step in this direction was made in 1833, when 

 fifty-six chronometers were transported in the steamer Hercules to 

 points along the shores of the Baltic Sea. This was followed by several 

 large or primary expeditions, fixing points from which smaller or sec- 

 ondary expeditions radiated as from centers. The most important of 

 these is the well-known expedition carried on under the direction of 

 Struve, for determining the difference of longitude between Greenwich 

 and Pulkova. The next was between Pulkova and Moscow, with forty 

 chronometers. During these exchanges a great number of box chro- 

 nometers were transported in carriages, and it was found that in a good 

 spring vehicle, even over bad roads, the rate of the chronometers were 

 as constant as when they were carried by water. In the frequent ex- 

 peditions following these, when no less than eighty chronometers 

 were employed, observations and comparisons were made not only at 

 the terminal points, but also at several intermediate stations. The 

 great number of chronometers in use made it necessary to find some 

 Uicans of lessening tbe time necessary for their comparison. When, as 

 was at first the case, siderial and mean time chronometers were com- 

 pared, 4 minutes were lost while waiting for a coincidence. As the out- 

 come of this necessity Struve invented the thirteen striker, that is, a 

 chronometer making thirteen beats or strokes in G seconds. This 

 gives, whether comparing with a star or mean chronometer, a coinci- 

 dence every G seconds within a range of 0".02, which is sufficiently accu- 

 rate. An uncompensated chronometer always formed a part of the 

 equipment, serving as a means for finding the temperature coefficients 

 of the compensated chronometers more satisfactorily than if tempera- 

 tures were taken from accompanying thermometers. As one would 

 expect, the Russians have made very elaborate investigations regarding 

 the rates of chronometers and their disturbing causes. 



As soon as Eussia was covered with a telegraphic net the new method 

 of determining difference of longitudes was tried and at once adopted 

 The first application of this scheme was in Finland, between the sta- 

 tions Cronstadt and Uleaborg. This was in I8G0, and since that time 

 each year has witnessed at least one new determination. In 1868 ob- 

 servations were made for finding the longitudes of Wiborg, Lovisa, Heb 

 singfors, and Albo with reference to Pulkova. In these operations 

 there was Uvsed for the first time the method of finding time by a tran- 

 sit instrument set in the vertical of Polaris. This method had been 

 known for along time, but had not been used because of the complicated 

 computations involved. But W. Dallen, of Pulkova, gave formulae and 

 tables which made it possible to compute the correction of the clock 

 almost as quickly as if the observations were made in the meridian. 



The greatest undertaking in the way of telegraphic longitudes are 

 the labors of Shamgorst and Kulberg, who, in 1873-'7G, gave a series of 



