succeed best with hypnotised persons—is extremely susceptible to suggestion of any kind. And his susceptibility is frequently increased by hyperaesthesia of the special senses, especially the sense of hearing. The strictest precautions are necessary, therefore, in all experiments conducted at close quarters, to ensure that no information shall reach him through the look, the gesture, or even the breathing of the bystander. In the cases cited in the next chapter the conditions of the experiment have been briefly indicated, but the reader is in all cases recommended to study the fuller records given in the publications of the Society.
There remains the question as to the nature of the transmission. When I tell a piece of news to a friend, a psychical state in me produces a corresponding psychical state in him. But we recognise that the psychical process proceeds pari passu with a physical process. The tension in my nerve centres provokes to action my organs of speech, which give rise to aerial waves, which in turn produce a physical change in friend's ears and so ultimately in his brain. Can any corresponding chain of physical causation be traced when the news is conveyed telepathically? So far as the experiments at close quarters are concerned, when the two parties are separated by a few feet or yards only, there is no difficulty in conceiving that the entire process may be susceptible of expression in physical terms. We have at either end of the
