earth. 
the center of the earth. This pull is nothing 
Therefore at the surface of the earth the fol 
Newton's laws, can be set: 
sually referred to as the 
sually designated as g. A 
experience a pull toward 
m 
miM \/ Mj^ 
y miM yj 
m 
where: 
gjn " 980 cm/sec2 = 980 gals = Mean acceleration at the 
earth's surface 
3 
M = 4/2 n e R = Mass of the earth 
m m 
^m = 5,52 = Mean density of the earth 
^m * 6367 km = Mean radius of the earth 
gal = Acceleration of one gram-mass equal one centimeter 
per second 
the earth have hieh mountain chains 
large extent and the oceans deep depressions of extent comparable to 
that 
to over 29000 feet above sea level at places. In spite of these variations 
in altitude of the surface of the earth, the earth can be taken, as the 
spheroid of revolution with its polar 
qual 
mately, respectively. The forces of gravity 
have been computed for this ideal 
usuallv ffiven in a table form as "Values of Theoretical 
Gravities on International Ellipsoid." 
gravity observations 
the gravitational values given in the table and 
3 
