98 Difference of Longitude, <^c. 



1868 we found the velocity on the land line to be 15,400 

 miles per second. 



Professor Harkness's temporary Observatory in Hobart 

 Town was situated in the Barrack-square in latitude 42° 

 53' 24-6" south, and by applying the above difference to 

 9h. 39m. 54-8s., the longitude of Melbourne, we get 9h. 49m. 

 20"46s. for the longitude of his station, which is marked by a 

 pier, which the Tasmanian authorities have promised to 

 preserve. Mr. Ellery has written to the Surveyor- General 

 at Hobart Town for the situation of this pier, with reference 

 to Fort Mulgrave, from which the longitude of the city has 

 been hitherto reckoned ; but as no reply has been as yet 

 received, I cannot say how this new determination of longi- 

 tude will agree with the old one. As a final result we have 

 then — 



Pier in Barrack-square, 



Latitude 42° 53' 24-6" South. 



Longitude 147 20 6'9 East of Greenwich. 



Note. — Since the above was written a letter has been 

 received from Prof Harkness, giving the results of his 

 triangulation in Hobart Town, according to which, adopting 

 the above position of the Pier in Barrack-square, the posi- 

 tions of the following places will be as under: — 



Lat. Long. 



Flagstaff at Prince of Wales Battery (Fort 



Mulgrave) 42° 53' 22-3" 147° 20' 36-3" 



Flagstaff at Queen's Battery 42 52 44-0 147 20 38-8 



Centre of front of St. David's Cathedral ... 42 53 6-9 147 20 10-2 



