In the same experimental setting, assume alternative explanations for melting have been properly excluded.
Minor premise: This wax is melted.
Major premise: In this closed setup, melting reliably indicates that the stipulated heating threshold was reached.
Conclusion: The wax reached that temperature.
Middle term: being melted. It is our evidence for the heating, but is not what causes the heating; it is an effect in this causal account.
The direction is therefore innī. Without exclusion of alternatives, the conclusion would not automatically be certain.