ASTRONOMICAL RESULTS OP PUBLIC SURVEYS. 301 



hands it made steady progress until his death in 1844." 

 Professor A. D. Bache was then appointed to take charge 

 of the survey, and has continued it to the present time. 



The astronomical part of this survey consists in de- 

 termining the latitude and longitude of the stations, and 

 the direction of the sides of the triangles with reference to 

 a meridian. 



Professor Bache has undertaken to determine the dif- 

 ference of longitude between Greenwich and the most 

 important points upon our coast, with the greatest pos- 

 sible precision. For this purpose he has availed himself 

 of all the astronomical observations previously on record, 

 and has instituted new observations, including those of 

 occultations and eclipses, moon culminations, and the ex- 

 change of chronometers. Numerous observations have 

 been made in Cambridge and its vicinity, in the neighbor- 

 hood of New York, Philadelphia, "Washington, and 

 other places. The difference of longitude between these 

 several places has been determined by means of the elec- 

 tric telegraph, so that observations at any of these places 

 are equally available for determining the longitude of 

 . each of them from Greenwich. 



Advantage has been taken of the frequent passage of 

 steamers between Boston and Liverpool, to make a 

 thorough comparison of the times of those ports by 

 means of chronometers. For this purpose, as soon as a 

 steamer arrives in Boston, its chronometers are taken to 

 Cambridge observatory for comparison, where they re- 

 main until the steamer is ready to return. Upon arriving 



