Five newly edited manuscripts reveal that the treatise De tonitruis purports to be adapted from the Irish language. In this essay, possible Irish affinities are explored and are found to lie, in increasing order of importance, in the ornate prose style, the recondite and culturally highly significant vocabulary, and the eulogistic citations of unnamed natural philosophers as authorities for thunder prognostics. In all these respects, De tonitruis differs from conventional European brontologies. Although it is surely not translated from the Irish language, the mark of Irish learning is distinctive.