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passed any point, the tension previously in store at that
point disappears, but not without having added, during the
infinitely small duration of its action, a due amount of
motion to that previously possessed by D. The nearer D
approaches to F, the smaller is the sum of the tensions re-
maining, but the greater is the living force ; the farther D
is from F, the greater is the sum of the unconsumed ten-
sions, and the less is the living force. Now the principle
of conservation affirms not the constancy of the value of the
tensions of gravity, nor yet the constancy of the vis viva,
taken separately, but the absolute constancy of the value
of the sum of both. At the beginning the vis viva was
zero and the tension area was a maximum ; close to F the
vis viva is a maximum, while the tension area is zero. At
every other point the work-producing power of the particle
D consists in part of vis viva and in part of tensions.

If gravity, instead of being attraction, were repulsion,
when the particles are in contact, the sum of the tensions
between two material particles D and F would be a maxi-
mum, and the vis viva zero. If D, in obedience to the
repulsion, moved away from F, vis viva would be gener-
ated; and the farther D retreated from F the greater
would be its vis viva, and the less the amount of tension
still available for producing motion. Taking repulsion into
account as well as attraction, the principle of the conserva-
tion of force affirms that the mechanical value of the ten-
sions and vires vivoe of the material universe is a constant
quantity. The universe, in short, possesses two kinds of
property which are mutually convertible, at an unvarying
rate. The diminution of either carries with it the enhance-
ment of the other, the total value of the property remain-
ing unchanged.

The considerations that we have here applied to gravity
apply equally to chemical affinity. In a mixture of oxygen
and hydrogen the atoms exist apart, but by the application

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