Journal of the Society for Psychical Research, 1908 #251230

There, I believe, was the mistake. The percipient, knowing beforehand that a given number of letters or notes would be sent, could not but try to guess, his mind entering into action, and that would, of course, prevent him from giving his undivided attention to the message sent. The percipient's mind must remain in a passive state, and his inward vision a perfect blank, in a state of expectation.