a British mathematician and logician. He formulated De Morgan's laws and introduced the term mathematical induction, making its idea rigorous. De Morgan was a brilliant and witty writer, whether as a controversialist or as a correspondent. De Morgan later in his life became interested in the phenomena of spiritualism. In 1849 he had investigated clairvoyance and was impressed by the subject. He later carried out paranormal investigations in his own home with the medium Maria Hayden.
