The main thread linking all the facts together in the present case is the hypothesis not only of continued or personal psychical existence in the abstract, but a definite inter-locking or inter-communication between two grades of existence,--the two in which we are most immediately interested and about which we can ascertain most,--that of the present and that of the immediate future for each individual; together with the added probabilities that the actual grades of existence are far more than two, and that the forthcoming transition, in which we cannot but be interested even if we do not believe in it, is only one of many of which we shall, in some barely imaginable way, in due time become aware. The hypothesis of continued existence in another set of conditions, and of possible communication across a boundary, is not a gratuitous one made for the sake of comfort and consolation, or because of a dislike to the idea of extinction; it is a hypothesis which has been gradually forced upon the author--as upon many other persons--by the stringent coercion of definite experience. The foundation of the atomic theory in Chemistry is to him no stronger. The evidence is cumulative, and has broken the back of all legitimate and reasonable scepticism. And if by selecting the atomic theory as an example he has chosen one upon which supplementary and most interesting facts have been grafted in the progress of discovery--facts not really contradicting the old knowledge, even when superficially appearing to do so, but adding to it and illuminating it further, while making changes perhaps in its manner of formulation--he has chosen such an example of set purpose, as not unlikely to be imitated in the present case also. CHAPTER I THE MEANING OF THE TERM LIFE "Eternal process moving on."--TENNYSON The shorter the word the more inevitable it is that it will be used in many significations; as can be proved by looking out almost any monosyllable in a large dictionary. The tendency of a simple word to have many glancing meanings--like shot silk, as Tennyson put it--is a character of high literary value; though it may be occasionally inconvenient for scientific purposes. It is unlikely that we can escape an ambiguity due to this tendency, but I wish to use the term 'life' to signify the vivifying principle which animates matter.