British chemist Sir William Crookes became interested in spiritualism due to which traumatic event?

Sir William Crookes (1832-1919) was a British chemist and physicist who attended the Royal College of Chemistry in London. He worked on spectroscopy (study of the interaction between matter and electromagnetic radiation). He was a pioneer of vacuum tubes, inventing the Crookes tube which was made in 1875. In 1913 Crookes invented 100% ultraviolet and 90% infrared blocking sunglass lenses.

Crookes became interested in spiritualism in the late 1860s. His interest was influenced by the death of his younger brother Philip in 1867 at the age of 21 from yellow fever, contracted while on an expedition to lay a telegraph cable from Cuba to Florida. In 1867, Crookes attended a seance to try to get in touch with his brother.

Crookes joined the Society for Physical Research, becoming its president in the 1890s. In 1890 he was initiated into the Hermetic Order of the Golden Dawn, a secret society devoted to the study and practice of the occult, metaphysics and paranormal activities. At the beginning of the 20th century he also joined the Theosophical Society and The Ghost Club, serving as president from 1907 to 1912.