140 
HAYFORD. 
the Salina base, on the thirty-ninth parallel arc, which serves 
also to control the lengths on a portion of the ninety-eighth 
meridian arc. But four more bases are necessary for this 
arc, one at the Rio Grande and three in the Dakotas. 
During the year 1900 two triangulation parties were in 
operation, one working northward in Nebraska and the other 
southward in Kansas. A base party of ten officers and men, 
which arrived on the working ground on July 16, 1900, in 
Nebraska, had by January 23, 1901, standardized the base 
apparatus twice, at the beginning and end of the season, and 
had measured the nine primary bases referred to above. 
The probable error of each base is less than one part in a 
million. If this feat of measuring nine bases, as well as 
standardizing the apparatus, in but little more than six 
months, while holding the accuracy up to the best standards 
of the past, is considered with reference to the moderate size 
of party and the time which has been required for former 
primary base measurements, it will be seen that there has 
been no lack of progressiveness along this line. 
One of the events of the year has been the connection of 
the gravity measures in the United States with those in 
Europe by swinging a set of the half-second pendulums, 
which serve to determine the relative values of gravity, at 
the base station at Washington and at the European stations 
at London, Paris, and Potsdam, at which the more impor¬ 
tant European absolute measures have been made. The re¬ 
sult of this expedition is to import, at a very small cost in 
time and money, the expensive and laborious determinations 
of the absolute value of gravity which have been made in 
Europe. 
During the last two years the instrument and the methods 
used in the precise leveling of the Coast and Geodetic Survey 
have been radically changed with a view to increasing both 
the accuracy and rapidity of the work.* The evidence as to 
the accuracy of the new work is rapidly accumulating and 
*See Proceedings of the American Society of Civil Engineers, Novem¬ 
ber, 1900, pp. 1113-1161. 
