Q40 PHILOSOPHICAL TRANSACTIONS. [aNNO 1723. 



of 4 to 1 , when the balls were as 1 and 2, the heavy and slowest ball broke 

 through but half the number of papers. It happened indeed sometimes, that 

 there was some little difference, when the papers were not equally strong, or 

 equally stretched, but the swiftest ball always broke through more papers than 

 the slow one. 



Now though this experiment at first seems to confirm Poleni's theory ; yet, 

 when duly weighed, it proves no such thing. For the lighter ball does not 

 break through more papers, because it has more force, or a greater quantity of 

 motion, but because each diaphragm has but half the time to resist the ball, 

 that falls with a double velocity, and therefore their resistance being as the time, 

 as many more of them must be broken by the swift ball, as by the slow one. 



P. S. To all the objectors, that allow the force of moving bodies, and their 

 quantity of motion to be the same, what has been said in this and my former 

 paper, seems to be a full answer ; but as there are now some philosophers, who 

 distinguish that force from the quantity of motion, I am obliged to say some- 

 thing more for clearing up that point. 



If I understand them right, they call vis viva a force, whose effect is sensible, 



as the force of gravity, when it accelerates bodies in their fall ; and vis mortua a 



force, which being destroyed, produces no sensible effect, as the force of gravity 



acting upon a weight in one scale of balance, when the weight cannot descend 



by reason of a counterpoise in the other scale. But certainly no man, that 



considers the thing attentively, would make that distinction. However, since 



Poleni allows that the quantity of motion in bodies, is as the mass multiplied 



into the velocity, or mv ; but says, that the force, with which they act, which 



he distinguishes by the name of vis viva, is as the mass multiplied into the 



square of the velocity, or mvv : I have made the following experiment to show 



his notion to be inconsistent ; though all the phaenomena of unequal weights 



applied to a statera, so as to make an equilibrium, might serve for that purpose, 



if it had not been objected, that the particular construction of the machine 



hindered it from agreeing with the supposed theorem, that the force is as the 



matter multiplied into the square of the velocity. 



Exper. Let two balls, A and b, fig. 22, be joined by a string, which going 

 through the smooth hole c of an even table, and under the pulley p, suspends 

 a weight w. It is plain, that on letting go the balls a and b, from the places 

 A and B, they will move towards c with the same force, because each of them 

 will be drawn towards c by half the force of the weight w, whether the balls 

 be equal, or unequal. 



1. The balls being of 2 ounces each, of ivory, were, at the same instant of 

 time, let loose from a and b, each distant 12 inches from c, and both came 



