The hypothesis is an attractive one; because it fits an agency which certainly exists, but whose effect is unknown, to an effect which certainly exists, but whose agency is unknown. In this world of vibrations it may seem at first the simplest plan to invoke a vibration the more. It would be rash, indeed, to affirm that any phenomenon perceptible by men may not be expressible, in part at least, in terms of ethereal undulations. But in the case of telepathy the analogy which suggests this explanation, the obvious likeness between the picture emitted (so to say) by the agent and the picture received by the percipient--as when I fix my mind on the two of diamonds, and he sees a mental picture of that card--goes but a very short way. One has very soon to begin assuming that the percipient's mind _modifies_ the picture despatched from the agent: until the likeness between the two pictures becomes a quite symbolical affair. We have seen that there is a continuous transition from experimental to spontaneous telepathy; from our transferred pictures of cards to monitions of a friend's death at a distance. These monitions may indeed be pictures of the dying friend, but they are seldom such pictures as the decedent's brain seems likely to project in the form in which they reach the percipient. Mr. L.--to take a well-known case in our collection (_Phantasms of the Living_, vol. i. p. 210)--dies of heart disease when in the act of lying down undressed, in bed. At or about the same moment Mr. N. J. S. sees Mr. L. standing beside him with a cheerful air, dressed for walking and with a cane in his hand. One does not see how a system of undulations could have transmuted the physical facts in this way. A still greater difficulty for the vibration-theory is presented by _collective_ telepathic hallucinations. It is hard to understand how A can emit a pattern of vibrations which, radiating equally in all directions, shall affect not only his distant friend B, but also the strangers C and D, who happen to be standing near B;--and affect no other persons, so far as we know, in the world.