By Daniel Simkin, IET Research Librarian

The image above shows the engraved title page of Martin Del Rio’s Disquisitionum Magicarum or Magical Investigations, published in Latin in 1603. It examines the practice of demonic magic and gives advice on how to identify and punish witches, as well as others who Del Rio regarded as heretics. Magical Investigations first appeared in 1599 and as an important work on demonology has been reprinted many times. The IET Archives holds two copies of Del Rio’s work, one in folio size from 1603 and another later edition in quarto size from 1679.

Although there are some differences between the editions in the engraved title pages, both show scenes of the Ten Plagues of Egypt from the book of Exodus. Moses is pictured performing miracles to persuade the Pharaoh to release the Hebrew people from slavery. The other figures in the scenes are the Pharaoh’s mystics whose magic is unable to counter the divine miracles of Moses. Del Rio draws a distinction in his book between miracles inspired by God and the magic performed by witches, as with the medieval distinction between “white” and “black” magic. He states that the devil cannot transcend nature’s laws, but God’s miracles can go beyond what is possible in nature.

The first four books of Magical Investigations examine a range of magical practices and describe many of the things we come to associate with witches and the occult today such as the ability to fly and transforming into animals. Del Rio describes the secret meetings that he believed witches held, regarding them as distorted versions of the Catholic Mass in which the devil would appear as a dog or goat and sacrifices would be carried out. His was one of the first works to describe this practice that is a familiar part of later literature and films on witches and the occult.

The final two books give practical guidance for judges when dealing with those who practised magic. Del Rio believed that magic came from the devil, as miracles came from God, and that to practise magic therefore treated the devil as God’s equal which would have been regarded as heresy.

Both editions of Magical Investigations are part of the library of Silvanus P. Thompson, which was purchased in 1917 by the IET. Although best known for his works on electricity, magnetism and acoustics, Thompson collected works on a diverse range of topics including astronomy, cartography, nature and several works on magic and mysticism.

In the 1603 edition Thompson has left a cutting from a catalogue of rare books, dated 1910 that notes that in Magical Investigations:

“This author in this curious old work, claims that Satan attacks lunatics at the full moon when their brains are full of humours; that in other cases of illness he stirs the black bile and in cases of blindness and deafness he clogs the eyes and ears.”

Who was Martin Del Rio?

Martin Del Rio was born in Antwerp in 1551 and was of Spanish descent. He was a prodigious scholar, enrolling at the University of Leuven in 1563 at the age of 12 and became fluent in nine languages. He later studied at the universities of Paris and Salamanca. Although Magical Investigations can be considered his most famous work, he also wrote a three-volume commentary on Seneca by the time he was 19 and other works on theology during his life.

Del Rio became a member of the Council of Troubles, a special tribunal set up on the orders of Philip II of Spain to punish the leaders of political and religious revolts against Spanish rule in the Netherlands. Academics disagree about the significance that his time as a young magistrate with the Council had on his writing of Magical Investigations. Whilst some historians claim that his role brought him into contact with supposed witches, there is considerable doubt that he ever encountered one or had much personal experience of witchcraft.

In 1579 Del Rio wrote to the Society of Jesus in Spain to enter the Jesuit Order, where he studied and taught theology at Jesuit colleges as well as undertaking missionary work. He travelled extensively throughout Europe visiting Austria, Belgium, France, Germany and the Netherlands. He died in Leuven in October 1608.

Magical Investigations is said to have been influential in the Salem Witch Trials of 1692-1693 although it is debatable how far the work was used in the actual hunting and persecution of witches. Some historians regard it as mostly restating ideas from already published works, in particular Malleus Maleficarum or Hammer of Witches, written in 1486. It continued to be reprinted into the 18th century and an English partial translation was published in 2000 by Manchester University Press.