302 HISTORY OF ASTRONOMY. 



in Liverpool, the chronometers are taken to the Liverpool 

 observatory, and their errors determined. This method 

 of comparison has been systematically pursued since 

 1844. During the year 1846, forty-two such compari- 

 sons were made. In 1848 the longitude of the Cam- 

 bridge observatory from Greenwich was determined by 

 IMr. Bond, from the transportation of 116 chronometers, 

 in thirty -four voyages of the Cunard steamers from Liver- 

 pool to Boston, to be 4h. 44m. 30'5s. The longitude 

 deduced from lunar occultations and solar eclipses is 

 4h. 44m. 31*9. During the year 1849, eighty-seven ad- 

 ditional comparisons were made, the results of which 

 differ nearly two seconds of time from those previously 

 obtained by astronomical observations. The mean result 

 of 175 chronometers was 4h. 44m. 30'ls., and it was be- 

 lieved that this result could not be one second in error. 

 The final result of the chronometric expeditions of 1849, 

 1850, and 1851 was 4h. 44m. 30'66s. During the pro- 

 gress of these expeditions, more than four hundred ex- 

 changes of chronometers have been made. 



The results of the coast survey must furnish additional 

 materials for determining the figure and dimensions of 

 the earth. The Atlantic coast embraces more than 

 twenty degrees of latitude, and its survey will virtually 

 furnish a measured arc of the meridian of that extent. 

 In several places the survey will furnish long continuous 

 arcs upon the same meridian. Thus from Nantucket 

 northward we shall obtain an arc of over three degrees ; 

 from Cape Lookout, northward along the shore of Chesa- 



