1X2 6f the Newtonian system,

These are but the first links in the chain ofNewton’s ideas : let us follow him a little fur-ther.—The earth is a globe, and gravity actsperpetually in straight lines which are perpen-dicular to its surface. Suppose a hole could bebored through it, and that a body was placed atthe center, what would be its weight ? Evidentlynothing: it would remain in the situation inwhich it was placed, unsuspended and unsup-ported. The force of gravity being always di-rected towards the center, it could have nopropensity to move either way, and would, there-fore, have no weight. For the same reason, if abody was thrown into this hole from the earth’ssurface, the velocity acquired, by the repeatedimpulses of gravity during the time of its fall,would carry it to the opposite extremity of theorifice, from whence it would again return, andcontinue to move backwards and forwards forever, if the medium had no resistance.

Since, therefore, a body, when placed at thecenter of the earth has no weight, we should beled to conclude from analogy, that, in descend-ing towards the center, its weight must be suc-cessively diminished; for it is not easy to con-ceive, that the gravity of a heavy body canchange immediately from a certain fixed quan-tity to nothing. And this doctrine, notwith-standing the impossibility of submitting it tothe test of experiment, is not only reasonable

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