The period between these successive appearances of the soul in a succession of physical bodies varies greatly and depends on a number of things. The length of time spent upon the astral plane has already been discussed. The time spent in the heaven world depends upon the mental and moral forces generated during the physical and astral life. If there is a great harvest of experience it will require a longer time to transmute it, while, of course, one who has thought little and loved but little will have a shorter period there, for it is the heart and head forces that have their culmination in the mental world. The question is a rather complex one and other factors come into play, including the intensity of the heaven world life. In general terms, however, it can be said that the heaven life of the ordinarily intelligent person will commonly be a period several times the length of his combined physical and astral life. Some people will have only two or three hundred years between incarnations while others may have six or seven centuries and still others a much longer period. In getting a right understanding of the subject of rebirth, or reincarnation, it is necessary to keep in mind the fact that the soul, or center of individualized consciousness, is the man and that the physical body is merely an instrument he uses for a number of years; that the causal body is his permanent body for the whole of human evolution; that the mental plane is his home plane and that from there he sends forth successive expressions of himself into these lower planes. With such facts before us there should be no confusion of thought about the successive personalities of an individual. Yet we sometimes hear people speak of the absurdity of supposing that a person can be one man in one incarnation and another man at a later rebirth. Of course no such thing occurs. An individual remains the same individual forever. "But," objects the critic, "may I not have been Mr. Jones, in England six hundred years ago, whereas I am now certainly Mr. Brown, in America at this moment? If so is that not a case of being two individuals?"