94 
This shows the necessity of referring this problem, viz., the adso- 
Jute determination of the intensity of the force of gravity, which 
belongs almost exclusively to the domain of physics, to as many 
different methods of solution as possible. For this purpose it does | 
not matter at which places the determinations are made, as the 
results obtained can always be closely compared with each other 
by means of relative determinations. 
The solution of many difficult problems is closely connected 
with the endeavor to ascertain the form of the geoid surface by 
means of gravity determinations. 
The discussion of the older pendulum observations, as well as the 
results of more recent determinations, have taught us that the distri- 
bution of the force of gravity on the surface of the earth is not 
regular, but that local and regional disturbances occur, and it ap- 
pears indispensable to ascertain their nature accurately. 
Even at the present time we know little about the influence 
which. the continents and seas, the mountains, plateaus and low 
plains, as wellas the various geological formations, exert upon gravity. 
The reductions which must necessarily be applied to the obser- 
vations, in order to make them comparable with each other, are 
not thoroughly understood ; at least, opinions about them still dif- 
fer considerably. Jastly, there is still a whole series of highly in- 
teresting but yet unexamined problems, which belong more to the 
domain of terrestrial physics, but which can also only be solved by 
determinations of gravity; so, for instance, the behavior of gravity 
beneath the surface of the earth, such as in the shafts of mines, in 
tunnels, etc. Experiments have been undertaken in this interest- 
ing problem in only three localities in Europe, viz., in the mines 
at Harton in England, Pribram in Bohemia, and Freiberg in 
Saxony. 
As we see, the problem to be solved by determinations of gravity 
is a very serious one; for, apart from the very numerous observa- 
tions distributed over the whole earth which are available for fur- 
nishing materials for the determination of the form of the surface 
of the geoid, we require for the thorough investigation of the prob- 
lems in connection with this subject, a large number of observing 
stations, amounting to thousands, and in close proximity to each 
other. It was impracticable to attain this end with the apparatus 
in use up to ashort time ago, for the observations were very trouble- 
some, and required much time, and were consequently costly. 
