The logic of the scientific method was set out by John Stuart Mill in 1843 and was
the method of difference. A simple example of what he
by this is to take two glasses of water which are identical in every
. Introduce a few drops of ink into one of these glasses. The water changes color!
to Mill’s method of difference it is safe to
that the change in the color of the water is due to the
of a new factor — the independent variable — in this case, the ink.