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

OR SCIENTIFIC METHOD. 285
known, it was practicable to estimate, with an approach to
accuracy, both the amount of the retardation and the amount
of the retarding causes or resistances, and to judge how near
they both were to being exhausted ; and it appeared that
the effect dwindled as rapidly as the cause, and at each step
was as far on the road towards annihilation as the cause
was. The simple oscillation of a weight suspended from a
fixed point, and moved a little out of the perpendicular,
which in ordinary circumstances lasts but a few minutes, was
prolonged in Borda s experiments to more than thirty hours,
by diminishing as much as possible the friction at the point
of suspension, and by making the body oscillate in a space
exhausted as nearly as possible of its air. There could
therefore be no hesitation in assigning the whole of the
and
retardation of motion to the influence of the obstacles ;
since, after subducting this retardation from the total pheno
menon, the remainder was a uniform velocity, the result was
the proposition known as the First Law of Motion."
The Method may be applied where exact measurement
is not possible ;
it is available whenever the intensities
of two phenomena can be compared, as they vary from
more to less or the reverse. A specially important case
for its application is when a phenomenon goes through
periodic changes i.e., alternately increases and decreases,
of which the tides are the most obvious example. If
other phenomena can be found which go through
changes in the same periods of time, there is probably
a causal connection between them and the first pheno
menon. This is the case with the apparent motions of
the sun and moon round the earth.
Mill lays down a fifth canon for a method which, like
that of Concomitant Variations, is specially appropriate
to quantitative investigations. This is the Method of
Residues. Its canon is thus stated by Mill :
"
Subduct
from any phenomenon such part as is known by
previous inductions to be the effect of certain ante-