Thomas Vaughan was widely known in his time as a writer on occult topics, apologist for the Rosicrucian Brotherhood (a sect whose members claimed arcane and magical knowledge), and alchemical experimenter. Many readers today encounter him first as the twin brother of the poet Henry Vaughan. To appreciate Thomas Vaughan's intellectual contributions, one must have a clear picture of his role in the Samuel Hartlib and Sir Robert Moray circles, which included future founders of the Royal Society as members. By recognizing the consistency of his schema, by studying his Neoplatonic and hermetic sources, and by acknowledging the qualities of Vaughan's mythopoeic imagination, one can place him more accurately in the intellectually turbulent decades of the Interregnum--at a time when the boundaries between science and magic were not yet set.

Thomas Vaughan was a descendant of an ancient Welsh family, the Vaughans of Tretower Court. One ancestor was...