Time after time astronomers have found seeming irregularities
in the planets’ motions, which they could not explain by, nor
deduce from this law of Newton’s (law of gravitation). In every
case, however, later investigations showed the fault to lie in
the imperfections of their methods; their calculations, or their
assumptions in regard to the number and size of the planets
were in error, not the law of gravitation. A discrepancy of
only two minutes between the observed and theoretical places of
Uranus led to the discovery of Neptune, and possibly the minute
discrepancy in the motions of Mercury may lead to important
discoveries regarding the properties or distribution of matter
in the neighborhood of the sun.--CHARLES LANE POOR,
“The Solar System.”
(1296)