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judging of the order of Nature, our inquiries eventually
relate to the permanence of force. From Galileo to Newton,
from Newton to our own time, eager eyes have been scan-
ning the heavens, and clear heads have been pondering the
phenomena of the solar system. The same eyes and minds
'have been also observing, experimenting, and reflecting on
the action of gravity at the surface of the earth. Nothing
has occurred to indicate that the operation of the law has
for a moment been suspended; nothing has ever intimated
that Nature has been crossed by spontaneous action, or
that a state of things at any time existed which could not
be rigorously deduced from the preceding state. Given the
distribution of matter and the forces in operation in the
time of Galileo, the competent mathematician of that day
could predict what is now occurring in our own. We cal-
culate eclipses before they have occurred, and find them
true to the second. We determine the dates of those that
have occurred in the early times of history, and find calcu-
lations and history at peace. Anomalies and perturba-
tions in the planets have been over and over again observed,
but these, instead of demonstrating any inconstancy on the
part of natural law, have invariably been reduced to conse-
quences of that law. Instead of referring the perturba-
tions of Uranus to any interference on the part of the
Author of Nature with the law of gravitation, the question
which the astronomer proposed to himself was, “ How, in.
accordance with this law, can the perturbation be pro-
duced ? ” Guided by a principle, be was enabled to fix the
point of space in which, if a mass of matter were placed,
the observed perturbations would follow. We know the
result. The practical astronomer turned his teleSCOpe tow-
ard the region which the intellect of the theoretic astrono-
mer had already explored, and the planet now named
Neptune was found in its predicted place. A very re-
spectable outcome, it will be admitted, of an impulse which

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