In the consideration of ascending bodies we have the direct opposite of the laws of falling bodies. When a body is thrown downward, gravity increases its velocity every second by the quantity g. When a body is thrown upward, gravity diminishes its velocity every second by the same quantity. Hence the time of its ascent will be found by dividing its initial velocity by g. The initial velocity of a body that can rise against the force of gravity for a given number of seconds is the same as the final velocity of a body that has been falling for the same number of seconds. (a.) The spaces traversed and the velocities attained during successive seconds will be the same in the ascent, only reversed in order. If a body be shot upward with a velocity of 321.6 feet, it will rise for ten seconds, when it will fall for ten seconds. The tenth second of its ascent will correspond to the first of its descent, i. e., the space traversed during these two seconds will be the same; the eighth second of the ascent will correspond to the third of its descent; the end of the eighth second of its ascent will correspond to the end of the second second of its descent.