RECENT PROGRESS IN GEODESY. 
3 
Britain. In simplifying the computations in office to corre¬ 
spond with the accuracy attained in the field, this country 
is easily foremost. 
The years 1898 and 1899 mark an epoch in the history of 
geodesy in the United States. In 1898 the last of the field 
operations on the great transcontinental arc, extending from 
the Atlantic to the Pacific along the thirty-ninth parallel, 
was completed. During the same year the field measures 
of the oblique arc parallel to the Atlantic coast were also 
completed. In 1899 the necessary observations to complete 
an oblique arc in California, extending from Point Arena to 
the Mexican boundary, were brought to a close. In 1899 
also, but little more than a year after the completion of the 
last field measurements, the computations connected with 
the arc of the thirty-ninth parallel were completed and the 
results put in form for the printer. 
To appreciate the full force of the above statements one 
must have a realizing sense of the great length of the above 
arcs. The combined length of all the arcs used by Colonel 
Clarke in 1880 to deduce the figure of the earth was equiva¬ 
lent to 89 degrees of a great circle. The arc of the thirty- 
ninth parallel is equivalent in length to 37 degrees of a great 
circle; the Atlantic oblique arc is 22 degrees long, and the 
California oblique arc 8 degrees; and the combined length 
of these three arcs is 67 degrees, or more than two-thirds the 
total length used by Clarke. 
The most interesting recent development in geodesy has 
been the investigations of variations of latitude. It may be 
asked, “ Why is this investigation classed as geodetic rather 
than astronomic?” The answer is, It belongs in both 
classifications. Obviously it is an astronomical investiga¬ 
tion, but it concerns the geodesist also; it concerns him 
directly, because the astronomical latitudes with which he 
must deal are now known to be a function of the time of 
observation. It is interesting to note also that many of the 
observations upon which our knowledge of the latitude 
variation depends were made with the zenith telescope, an 
