Full Idea
It is clear to the senses that hot water, if left to its own nature, reverts to coldness; this coldness cannot be caused by anything other than the substantial form of the water.
Gist of Idea
Hot water naturally cools down, which is due to the substantial form of the water
Source
William of Ockham (Seven Quodlibets [1332], III.6), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 24.4
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.561
A Reaction
Unfortunately this is very bad science (even for its time), but it shows how many scholastics treated hylomorphism as a very physical and causal theory.
Related Idea
Idea 16756 Substantial forms must exist, to explain the stability of metals like silver and tin [Albertus Magnus]