754 Afr. Hutton’s Calculations to afcer tain 
the whole fpace below this horizontal plane were full of 
matter to an equal extent both ways, its attraction need 
not be computed, as thofe on the contrary fides would 
mutually balance each other; but fince there are unequal 
vacuities on each fide, it is evident, that the attraction of 
the matter that might be contained in them mull be de- 
ducted from the other two equal quantities, to leave the 
real attraction of thofe two fides; then fub trading the 
remainder to the South fide from that of the Northern 
fide, there will at laft remain the joint effect of all the 
matter below the plane in the Northern direction : but 
as the one remainder is to be fubtracted from the other, 
the two equal quantities may be omitted in both, and 
only the effects of the vacuities brought into the account, 
which being twice fubtracted, their figns become con- 
trary to thofe of the parts above the horizontal plane ; 
that is, the effect of the Southern vacuity is affirmative, 
and that of the Northern one negative. But for the 
Northern obfervatory, when the attraction towards the 
South is to be found, the contrary names take place; 
that is, in the elevations the Southern parts are affirma- 
tive, and the Northern parts negative; but in the vacui- 
ties or depreffions, the Northern parts are affirmative, 
and the Southern ones negative. 
According 
