Intended as a supplement to Sir Walter Scott's 1830 Letters on Demonology and Witchcraft, this 1832 publication seeks to explain and expose the science behind the alleged 'magic' of spiritualists and conjurors. David Brewster (1781–1868), a Scottish natural philosopher and historian of science, was highly regarded in his lifetime but has since faded into obscurity. Penned at the request of Scott, Brewster's friend and neighbour, this book follows an epistolary structure, consisting of thirteen letters each addressing and exposing different aspects of the alleged supernatural activity, in keeping with the format of Scott's publication. Brewster's subject matter includes optics, magic lanterns, automata, alchemy, fire-breathing, spontaneous combustion, spectral illusions and various other phenomena. In each case he carefully outlines how this 'magic' is created with optical illusion, narcotic drugs, gas inhalation, and chemical tricks. The book offers an intriguing insight into nineteenth-century attitudes towards the supernatural.