44 SCIENCE PRIMERS. [MATERIAL 



greater space in a given time, say a second, than that 

 through which its gravity would, in the same time, 

 impel it downwards. 



But the distance which the water will travel during 

 this second will be the difference between the distance 

 which it would have ascended if there had been no 

 gravity forcing it down, and the distance which it 

 would have descended if there had been no momentum 

 driving it up ; and, at the end of the second, the rate of 

 its motion upwards, or its velocity, will be proportion- 

 ally slower. Thus, at the end of the first second, the 

 water has spent a certain portion of its momentum in 

 overcoming its gravity. And as there is nothing to 

 make good the loss, it would, if left to itself, travel 

 more slowly, or over a less distance, in the second 

 second than it tended to do in the first. But though 

 the momentum of the water is diminished, its gravity, 

 weight, or tendency to fall downwards, for a given 

 distance in a second, remains exactly what it was, and 

 operates in the course of the second second to exactly 

 the same extent as in the first. Hence, at the end of 

 the second second, the distance through which the 

 water travels upwards is still smaller, and its velocity 

 is still more diminished. It is obvious that, however 

 great the disproportion between momentum and gravity 

 to start with, gravity must gain the day in the long run 

 under these circumstances. The store of momentum 

 will be used up ; and, after a momentary rest, the 

 water, reduced to the condition of a body without 

 support, will begin to be carried downwards by the 

 unopposed action of gravity. 



The case is similar to that of a boy sculling a boat, 

 the bows of which are suddenly seized and the boat 



