On the 17th of December 1910, during a strong gale, the lighthouse keeper at the Arranmore North station reported an alarming and mysterious occurrence. He spotted what he described as a ‘blueish phosphorescent light’ appearing on the station’s lightning conductor, where it remained for several minutes. The lighthouse keeper was quite mystified by this and sent word of the phenomenon to Irish Lights headquarters in Dublin. His description of the phenomenon and his correspondence with Irish Lights’ Head Office are present in this file.

The Commissioners contacted their scientific advisor, Sir Robert Stawell Ball. In addition to advising the Commissioners on scientific matters, he was a Professor of Astronomy and Geometry at Cambridge University, Royal Astronomer of Ireland and winner of the Royal Irish Academy’s Cunningham Medal. He had a planet named after him, 4809 Robertball posthumously in 1928. Luckily, he was able to recognise the blue light as an example of a phenomenon known as St. Elmo’s fire. This file contains Sir Ball’s identification of the phenomenon, in addition to a wish to travel to the island to witness it in person. Whether he made this journey is uncertain, as he passed away three years later.

St. Elmo’s Fire occurs during storms when there is high voltage in the air between the ground and a storm system. This voltage tears apart air molecules and causes gasses in the air to glow. St. Elmo’s Fire is made of plasma, the same substance which makes up lightning and neon signs. It takes its name from St. Erasmus, the patron saint of sailors. Its blue colour is due to the nitrogen and oxygen gasses present in earth’s atmosphere. Sightings of St. Elmo’s Fire have been recorded in the works of Julius Caesar, Magellan and Charles Darwin, so Arranmore’s lighthouse keeper unknowingly joined some esteemed company during his mysterious night.