the Universe was the first serious attempt by a biologist to evaluate the likelihood of life on other planets. He concluded that the Earth was the only planet in the solar system that could possibly support life, mainly because it was the only one in which water could exist in the liquid phase. His treatment of Mars in this book was brief, and in 1907, Wallace returned to the subject with a book Is Mars Habitable? to criticise the claims made by the American astronomer Percival Lowell that there were Martian canals built by intelligent beings. Wallace did months of research, consulted various experts, and produced his own scientific analysis of the Martian climate and atmospheric conditions. He pointed out that spectroscopic analysis had shown no signs of water vapour in the Martian atmosphere, that Lowell's analysis of Mars's climate badly overestimated the surface temperature, and that low atmospheric pressure would make liquid water, let alone a planet-girding irrigation system, impossible. Richard Milner comments that Wallace "effectively debunked Lowell's illusionary network of Martian canals." Wallace became interested in the topic because his anthropocentric philosophy inclined him to believe that man would be unique in the universe. Other activities Spiritualism Wallace was an enthusiast of phrenology. Early in his career, he experimented with hypnosis, then known as mesmerism, managing to hypnotise some of his students in Leicester. When he began these experiments, the topic was very controversial: early experimenters, such as John Elliotson, had been harshly criticised by the medical and scientific establishment. Wallace drew a connection between his experiences with mesmerism and spiritualism, arguing that one should not deny observations on "a priori grounds of absurdity or impossibility". Wallace began investigating spiritualism in the summer of 1865, possibly at the urging of his older sister Fanny Sims. After reviewing the literature and attempting to test what he witnessed at séances, he came to believe in it. For the rest of his life, he remained convinced that at least some séance phenomena were genuine, despite accusations of fraud and evidence of trickery. One biographer suggested that the emotional shock when his first fiancée broke their engagement contributed to his receptiveness to spiritualism. Other scholars have emphasised his desire to find scientific explanations for all phenomena. In 1874, Wallace visited the spirit photographer Frederick Hudson. He declared that a photograph of him with his deceased mother was genuine. Others reached a different