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step, into every branch of physical astron-
omy; giving the physical meaning of Ke-
pler’s three laws, and explaining, or indicat-
ing the explanation of, all the known heav-
enly motions and their irregularities; show-
ing that all of these were included in his
simple statement about the law of universal
gravitation; and proceeding to deduce from
that law new irregularities in the motions
248