6 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



cal of the polar star is especially based upon the experience 

 gained in the summer of 1868, and in subsequent years. 

 Previous to this time, in fact, the few transit instruments 

 that had been specially adapted to his method were required 

 for use in other places; and it was only in 1868 that some 

 of them could be employed by the persons who were ac- 

 quainted with his methods, in connection with the measure- 

 ment of a degree of longitude under the sixtieth parallel of 

 north latitude. In the fall of the same year, eight astronom- 

 ical stations were occupied by his geodetic students in the 

 neighborhood of the Duderhof mountain, near St. Peters- 

 burg, whose positions were determined in connection with 

 tlie investigation of the local deviation of the pendulum. 

 Dollen^Die Zeithestimmimg. Second Memoir. 



ACCURACY OF CHRONOMETERS. 



An excellent investigation having been made by Lieu- 

 tenant Martin, of the French navy, into the accuracy of the 

 chronometers actually ^lsed on two voyages of circumnavi- 

 gation in 1866 to 1868, he states that, first, in most cases, it 

 is necessary to take account of the acceleration in the daily 

 rate of the chronometer, as proportional to lapse of time. 

 Second, that in relying upon one or two chronometers we 

 risk the chance of doubling our errors, if we make any em- 

 pirical correction for the temperature. Third, with three or 

 more chronometers, we should make a correction for the tem- 

 perature. Revue 3Iaritime et Coloniale^ Sept.^ 1875, 402. 



ON TERRESTRIAL REFRACTION. 



A series of observations has been made by Stebnitzky, 

 colonel on the staff in the Russian army, looking to the im- 

 provement of our knowledge of terrestrial refraction. His 

 observations were made mostly in the plains to the north of 

 the Caucasus, and in a mountainous country. The instru- 

 ment employed was a vertical circle, made by Messrs. Ertel, 

 at Munich. The reduction of the observations and the de- 

 duction from them of some corrections to the terrestrial re- 

 fraction has been made by Sawitsch. In general, he finds 

 that the observations have been made between the epochs of 

 tranquil images of the stars in the morning and evening ; 

 and that perhaps the terrestrial refractions thus observed 



