THE FORCE OF GRAVITY ON THE OCEAN. 
137 
also to have suggested some years ago that the force of gravity 
on the ocean might be determined in this manner. 
A method analogous to that of Mohn was suggested some 
years ago by Freiherr v. Wiillersdorff Urbair, using in place 
of the hypsometer an aneroid barometer (Das Aneroid als 
Instrument zur Messung der Aenderung der Schwere, Zeit- 
schr. d. osterr. Gesell. f. Meteorologie, Bd. I., 1866, Seite 97). 
Until the immediate present, however, the indications of all 
instruments like the aneroid have proved untrustworthy, 
owing to the irregular variations of the elasticity of metals. 
A remedy has recently been found for this by keeping the 
instrument under a contant atmospheric pressure, except 
during the brief interval necessary for observation. By 
means of this method a distinct advance seems to have been 
achieved, and the application of the aneroid to the measure¬ 
ment of the variation of the force of gravity is much more 
feasible than hitherto. As the result of a comparison made 
in 1898 between one of these improved aneroids and a mer¬ 
curial barometer, it is stated that the extreme differences 
between the indications of the two instruments were +1.7 mm. 
and — 0.8 mm., although the test covered a range in height 
of 3,800 meters and extended over a period of six weeks. 
