The subconscious usually took time to absorb and react. That was another thing his father had taught him to observe. Learn something, and it takes from days to months for it to become lodged in the subconscious and to rise into operation naturally from there. John Henderson had taken six weeks to vanish after having learned the theory. It had taken Horace Smith three and a half days, but he had had the added factor of Dr. Henderson's disappearance to trigger reactions. The theoretical physics class had taken three days exactly, and its vanishing had been a sort of group action or chain reaction, with intensely emotional reaction after the first student had vanished before the eyes of the others. His own father, originator of the theory, had probably fallen into the trap of starting to believe after Horace had vanished, so it became a greater probability that the disappearance was related to knowledge of the theory. Seeing the students vanish had probably set up an emotional state where complete belief was precipitated. In the whole series the only improbable part was that so many students would react in the same short time. That was partly nullified by the fact that it was a special class, and only high I.Q. students with excellent records were accepted. They would tend to be somewhat identical in reaction times. He straightened up and stared through the windshield at the dark street. So there it was, the probable mechanism of vanishment. A system was fed into the conscious mind. The conscious mind accepted it. In due time that system was transferred down into the matrix that held the person in this reality or universe. Once there, it made the whole person _transfer_ to a system where the altered matrix fitted. It might not be the system pictured in his father's theory. It might be a compromise system. _Where_ and _when_ probably had no meaning in relation to the two systems. That was why, when the shift came, the person vanished instantly without any strange manifestations of any kind. Was it reversible? If so, then some of those who had vanished would reappear eventually. A sudden, startling thought made Fred sit up straight, his eyes shining with excitement. So far he had been safe mainly because he habitually didn't attach belief to anything. His other facet of difference might be the means of his testing this without real danger of vanishing. Could he dredge up from the deepest layers of unconscious thought, the threads leading directly to the matrix that held him in his surroundings and learn consciously what it was? A thought. He reflected on it, then decided before he made any decisions he would explore the other avenue, the one the police had naturally thought of.