An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

OR SCIENTIFIC METHOD. 295
without entering into mathematical details, to explain
the process by which the ultimate suggestion was brought
under his consideration ; and it would be equally so to
convey an idea of the immense mass of calculation
through which he toiled in putting each of his successive
theories to the test of agreement with the observations.
Finally, after working his way
in alternate exultation at
anticipated triumphs, and bitter disappointment when,
one after another, they vanished in air, driving him, as
he says, almost to insanity/ he at length had the
intense gratification of finding that an elliptic orbit de
scribed about the sun in one of the foci agreed accurately
with the observed motions of the planet Mars." 1 The
irregularity of its movement vanished ; all its observed
positions became intelligible, were "explained," when
seen to be successive points on this simple and symmetri
cal curve. The hypothesis, thus proved for Mars, was
extended by analogy to the other known planets, and
proved true of them also, by observations as accurate as
were then available, Kepler perceiving that his original
assumption as to the motion of the earth was only an
approximate one. Thus was established
"
Kepler s first
Law." There could be no better instance of how dis
connected facts are
"
explained
"
by being brought under
general laws. In s Kepler case the law had to be dis
covered ; but in the same sense we
"
"
explain an event
when we can show it to be a new instance of a known
law.
(b) We may "explain" law by law. Of such ex
planation there are two kinds. A given law may be
shown to result from the combined operation of other
laws. Thus, the motion of a projectile, if we neglect
the resistance of the air, is a parabola. This is
1 Baden Powell, History of Natural Philosophy, p. 150.
"
ex-