Let us consider now, as an illustration of the method of the abstract sciences, the well-known case of the discovery of the planet Neptune. This planet was discovered by calculation and deduction, and was only seen when its position had been so accurately determined that the astronomers who searched for it knew exactly the point of the heavens to which to direct their telescopes. The calculation was one of extraordinary intricacy, and was made independently by two mathematicians, Adams of Cambridge and Leverrier of Paris, between the years 1843 and 1846. Each communicated his result independently--Adams to the astronomer Challis, the Director of the Cambridge Observatory, and Leverrier to Dr. Galle of the Berlin Observatory. Within six weeks of one another and entirely unknown to one another, in August and September 1846, each of these astronomers observed the planet where he had been told to look for it. This is one of the romances of modern science. It is not the discovery but the method that led to it which may throw light on our problem of the nature of truth. At first sight this seems exactly to accord with and even to illustrate the pragmatist theory, that truth is what works. The investigation is prompted by the discrepancies between the actual and the calculated positions of Uranus, the outermost planet, as it was then supposed, of the system. This revealed a need, and this {60} need was met by the practical postulate of the existence of another planet as yet unseen. The hypothesis was found to work even before the actual observation put the final seal of actuality on the discovery. What else but the practical consequences of the truth claim in the form of the hypothesis of an undiscovered planet were ever in question? Yes, we reply, but the actual method adopted, and the knowledge sought for by the method, are precisely of the kind that pragmatism rejects as "useless" knowledge. Why were not the observed movements of Uranus accepted as what they were? Why was it felt that they must be other than they were seen to be unless there was another planet? The need lay in the idea of system. It was inconsistent with the system then believed complete, and the need was to find the complete system in which it would harmonise. The truth that was sought for was a harmonious individual whole, and the method employed precisely that which the Absolutist theory of reality employs. There is observed a discrepancy, an inconsistency, a contradiction within the whole conceived as a system. This negation is treated as a defect, is calculated and accurately determined, and is then positively affirmed of the reality. Now, what is distinctive in this method is that reality is conceived as a complete system. If the felt defect in this system cannot be made good by direct discovery, its place is supplied by a fiction, using the term in its etymological meaning to express something made and not in its