Prof. Lovering on the American Prime Meridian. 191 
character which has been given for the proposed change 1s 
founded upon the slight error which still affects the best deter- 
mined American longitudes as reckoned from Greenwich, arising 
from our ignorance of the exact breadth of the Atlantic ocean. 
Assuming the uncertainty which still exists in the corrected lon- 
gitude of Boston to amount to two seconds of time, as stated by 
Lieut Davis, this is equivalent to an error of about half a mile in 
longitude. Half a mile, under the circumstances, is a large error 
for the astronomer; but to the navigator, who will compare it 
with other errors to which he is exposed, it will appear quite in- 
significant. 'The best chronometers, transported in the Britis 
teamers between Liverpool and Boston, are liable to vary four 
seconds. The errors incidental to the lunar method of calcula- 
Sea. hether the error is large or small, important or unimpor- 
tant, the proposed change of the prime meridian from Greenwich 
age with its chronometers arranged to an American prime merid- 
‘an. The same difficulties will reappear, though in an inverted 
order. ‘The captain leaves home with his chronometers set to 
true American time, but he cannot tell within two seconds the 
longitude of his European port, and on this account, when he is 
Omeward bound, his chronometers must be stamped by the same 
error of two seconds. In other words, if we do not know the 
€xact distance from Liverpool to Boston, neither do we know any 
