Electric Pentacle

The "electric pentacle" is a fictional electronic device invented by author William Hope Hodgson and used in several of his short stories about Carnacki the Ghost-Finder.

The device consists of a series of wires and glowing vacuum tubes, and so was a realistic portrayal of electronic technology in the early 20th century. Its purpose, however, was more speculative: it is designed to protect the investigator against malign ghosts or other spiritual manifestations. Hodgson's fictional detective of the supernatural uses it in combination with a more traditional protective magical pentacle, and thus combines the traditional protective power ascribed to the pentacle with pseudo-scientific theories about spiritual "vibrations," connected to the then-popular Spiritualism.

Hodgson describes the elaborate setup Carnacki employs before spending the night in allegedly haunted room in the story "The Gateway of the Monster". He first describes construction of the more traditional protective arrangement:

"...I returned then to the center of the room, and measured out a space twenty-one feet in diameter, which I swept with a 'broom of hyssop.' About this, I drew a circle of chalk, taking care never to step over the circle. Beyond this I smudged, with a bunch of garlic, a broad belt right around the chalked circle, and when this was complete, I took from among my stores in the center a small jar of a certain water. I broke away the parchment, and withdrew the stopper. Then, dipping my left forefinger in the little jar, I went 'round the circle again, making upon the floor, just within the line of chalk, the Second Sign of the Saaamaaa Ritual, and joining each Sign most carefully with the left-handed crescent. I can tell you, I felt easier when this was done, and the 'water circle' complete. Then, I unpacked some more of the stuff that I had brought, and placed a lighted candle in the 'valley' of each Crescent. After that, I drew a Pentacle, so that each of the five points of the defensive star touched the chalk circle. In the five points of the star I placed five portions of the bread, each wrapped in linen, and in the five 'vales,' five opened jars of the water I had used to make the 'water circle.' And now I had my first protective barrier complete."

After completing this, Carnacki adds the technological components as a second layer of defense:

"I turned-to now to fit the Electric Pentacle, setting it so that each of its 'points' and 'vales' coincided exactly with the 'points' and 'vales' of the drawn pentagram upon the floor. Then I connected up the battery, and the next instant the pale blue glare from the intertwining vacuum tubes shone out."

The electric pentacle is not omniprotective against spiritual manifestations. Some classes of malign entities, particularly those Hodgson labels as "Saiitii" manifestations, as opposed to the less potent "Aeirii," are capable of overpowering its defensive capacities easily. The electric pentacle also offers no defense against phony "ghosts."

"The Gateway of the Monster" contains two different plot twists that demonstrate loopholes in the efficacy of the protective barrier: as the entity flies directly towards him, startling him, Carnacki with a reflexive twitch knocks over part of the protective barrier, leaving a temporary gap, and is barely able to restore it before the entity breaches the barrier. Later, Carnacki accidentally allows the entity to manifest itself inside the pentacle with him; this clearly does him no good. Fortunately, he is able to cross the pentacle and escape while the entity cannot, and so he is again protected from it.

In the later Carnacki story "The Hog," a variation of the electric pentacle appears. This is a device that uses glowing glass tubes (modeled, perhaps, after neon tubes) to generate different colors. The colors are supposedly defensive against different varieties of supernatural influences. The story becomes complex as Carnacki puzzles out a sequence of crossings and rearranging of the colored tubes designed to allow him and an unconscious friend to escape the protective ring while preventing the escape of a terrifying manifestation of a giant hog.