Many other writers have given us examples and instances of the operation of the out-of-consciousness planes of thought. One has written that when the solution of a problem he had long vainly dealt with, flashed across his mind, he trembled as if in the presence of another being who had communicated a secret to him. All of us have tried to remember a name or similar thing without success, and have then dismissed the matter from our minds, only to have the missing name or thought suddenly presented to our conscious mind a few minutes, or hours, afterwards. Something in our mind was at work hunting up the missing word, and when it found it it presented it to us. A writer has mentioned what he called "unconscious rumination," which happened to him when he read books presenting new points of view essentially opposed to his previous opinions. After days, weeks, or months, he found that to his great astonishment the old opinions were entirely rearranged, and new ones lodged there. Many examples of this unconscious mental digestion and assimilation are mentioned in the books on the subject written during the past few years. It is related of Sir W. R. Hamilton that he discovered quarternions one day while walking with his wife in the observatory at Dublin. He relates that he suddenly felt "the galvanic circle of thought" close, and the sparks that fell from it was the fundamental mathematical relations of his problem, which is now an important law in mathematics. Dr. Thompson has written: "At times I have had a feeling of the uselessness of all voluntary effort, and also that the matter was working itself clear in my mind. It has many times seemed to me that I was really a passive instrument in the hands of a person not myself. In view of having to wait for the results of these unconscious processes, I have proved the habit of getting together material in advance, and then leaving the mass to digest itself till I am ready to write about it. I delayed for a month the writing of my book 'System of Psychology,' but continued reading the authorities. I would not try to think about the book. I would watch with interest the people passing the windows. One evening when reading the paper, the substance of the missing part of the book flashed upon my mind, and I began to write. This is only a sample of many such experiences." Berthelot, the founder of Synthetic Chemistry has said that the experiments leading to his wonderful discoveries have never been the result of carefully followed trains of thought--of pure reasoning processes--but have come of themselves, so to speak, from the clear sky. Mozart has written: "I cannot really say that I can account for my compositions. My ideas flow, and I cannot say whence or how they come. I do not hear in my imagination the parts successively, but I hear them, as it were, all at once. The rest is merely an attempt to reproduce what I have heard."