Sidgwick did not work alone. Eleanor Sidgwick, a mathematician who became principal of Newnham College, Cambridge, was in practice the more rigorous investigator of the two, and it was largely she who exposed several of the physical mediums the society examined, publishing detailed accounts of how the effects had been produced.
Together with the group around them the Sidgwicks conducted the Census of Hallucinations in the early 1890s, an attempt to establish by survey how often people experience an apparition and how often such an experience coincides with a distant death. Their conclusion after nearly two decades is the part worth preserving. Sidgwick stated in his presidential addresses that he was not appreciably nearer to a settled conviction than when he began, and that the accumulation of testimony had not carried him where he had hoped it would. Coming from a man who had given eighteen years to the effort and had every personal motive to conclude otherwise, that is a more useful datum than most of the case reports the society published, and it is the standard against which later confident summaries of the same evidence should be read. Eleanor Sidgwick outlived him by four decades and continued the work, publishing critical assessments of mediumship well into the twentieth century.