Nobody asked but …
Determining the critical difference is the key.
From Dictionary of Philosophy
Mill’s methods: Inductive methods formulated by John Stuart Mill for the discovery of causal relations between phenomena.
Method of Difference: If an instance in which the phenomenon under investigation occurs, and an instance in which it does not occur, have every circumstance in common save one, that one occurring in the former; the circumstance in which alone the two instances differ, is the effect, or the cause, or an indispensable part of the cause, of the phenomenon.
— Kilgore Forelle
For Mill’s Method #1, go here