 Dom Augustine Calmet , a French theologian and scholar , put together a comprehensive treatise in 1751 titled Treatise on the Apparitions of Spirits and on Vampires or Revenants which investigated the existence of vampires , demons , spectres and many other matters relating to the occult of his time . Calmet conducted extensive research and amassed reports of vampire incidents and extensively researched theological and mythological accounts as well . He had numerous readers , including both a critical Voltaire and supportive demonologists who interpreted the treatise as claiming that vampires existed . In his Philosophical Dictionary , Voltaire wrote : 
