Epsesin, pepsin, pepansin, aptesin

Meaning

Nature lists these four learned fire-names when insisting that appropriate matter alone is insufficient without the proper fire. They stand beside natural, contrary-to-nature, unnatural and non-burning fire, and beside paired elemental qualities. The supplied passage does not separately define the four names or securely assign each to one item in the adjoining lists. The English therefore retains them rather than offering four confident modern equivalents. Their local purpose is to demand discrimination among modes of heat and operation within Nature's teaching, not to license an invented taxonomy or an executable heating schedule.