Annual Report on the U.S. Coast Survey. 311 
“The accuracy with which a remeasurement of considerable 
length could be made, was tested more than once in the measure- 
is physically most improbable, about five-tenths of an inch.” 
of the new Catalogue of Stars by the British Association, gives 
8reat facility in the use of this method, as well as accuracy in 
the results. At one station the mean probable error of a single 
rmination, as deduced from the comparison of the several in- 
dividual observations, was but four-tenths of a second of space, 
and at another but one-tenth. All the astronomical and other ob- 
servations have been reduced to a system, in which numerous in- 
dividual observations are scrutinized, and the limit of errors ob- 
_ tamed by the method of least squares, which is now constantly 
ssed as a part of the plan of observation. By means of it the 
different instruments, which have on any occasion been used at 
the same place, can be compared, and in this way the superiority 
of the zenith telescope, as far as the comparison has yet been 
N astronomical station has been established at Nantucket, 
Which is an imp rtant position on account of its being the south- 
ern extremity of the longest arc of the meridian to be found on 
