Before revision: If the parcel is displaced by a small vertical increment , and it maintains its original density , so that its volume does not change, it will be subject to an extra gravitational force against its surroundings of: where is the gravitational acceleration, and is defined to be positive.
After revision: If the parcel is displaced by a small vertical increment and it maintains its original density , so that its volume does not change, it will be subject to an extra gravitational force against its surroundings of: where is the gravitational acceleration, and is defined to be positive.