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Leihnitian Dodrine, if my Argument drawn from k 
can receive a clear and fatisfadtory Anfwer. 
Experiment . 
Upon an horizontal Plane, at Reft, but move- 
able with the ieaft Force, fuppofe upon a Boat in 
a ftagnant Water, let there be placed, between two 
equal Bodies, a bent Spring, by the unbending of 
which the two Bodies may be pufhed contrary Ways. 
In this Cafe it is evident, that the Velocities, 
which the two Bodies receive from the Spring, will 
be exactly equal, and their moving Forces will alfo 
be exadly equal 5 and that the Plane they move upon, 
and alfo the Boat upon which it lies, will have no 
Motion given them either Way. Let us call the 
Velocity of each Body 1, and the moving Force 
alfo 1. 
Now, let us fuppofe the Spring to be bent afrcfh 
to the fame Degree as before, and to be again placed 
between the two Bodies lying at Reft } then let the 
Plane, upon which the Spring and the Bodies lie, 
be carried uniformly forwards, in the Diredion of 
the Length of the Spring, with this fame Velocity 1. 
In this Cafe it is manifeft, that each of the Bodies will 
have the Velocity x, and the moving Force 1, both 
in the Diredion of the Axis of the Spring. 
During this Motion, let the Spring again unbend, 
and pufh the two Bodies contrary Ways, as before, 
the one forwards, the other backwards: Then the 
Spring will give to each of thefe Bodies the Velocity 
1, as before, when the Plane was at Reft. 
By this means the hindmoft Body, or that which 
is pufhed backwards, will have its Velocity 1, which 
it 
