"There remains one all-important consideration," he went on swiftly. "Magic appears to be a science which markedly depends on its environment--that is, the situation of the world and the general conditions of the cosmos at any particular time. For example, Euclidean geometry is useful on Earth, but there are regions--and it would be easy to imagine more--in which a non-Euclidean geometry is more practical. The same is true of magic, but to a more striking degree. The basic, unstated formulas of magic appear to change with the passage of time, requiring frequent restatement--though it might conceivably be possible to discover master-formulas governing that change. It has been speculated that the laws of physics show a similar evolutionary tendency--though if they do evolve, it is at a much less rapid rate than those of magic. It is natural that the laws of magic should evolve or change more swiftly, since magic depends on a contact between the material world and another level of being--and that contact is complex and may be shifting rapidly. "Take astrology, for example. In the course of several thousand years, the precession of the equinoxes has put the Sun into entirely different celestial houses--signs of the Zodiac--at the same times of year. A person born, say, on March 22nd, is still said to be born in Aries, though he is actually born when the Sun is in the constellation Pisces. A failure to take into consideration this evolutionary change since the formulas of astrology were first discovered, has rendered the formulas obsolete and invalidated them for--" "It is my belief," the voice broke in, like a phonograph suddenly starting, "that astrology has always been largely invalid. That it is one of the many pretended sciences which have been confused with true magic and used as a kind of window dressing. Such is my belief." "I presume that may be the case, and it would help to explain why magic itself has been outwardly discredited as a science--which is the point I'm getting at. "Suppose the basic formulas of physics--such as Newton's three laws of motion--had changed several times in the last few thousand years. The discovery of any physical laws at any time would have been vastly more difficult. The same experiments would give different results in different ages. But that is the case with magic, and explains why magic has been periodically discredited and has become repugnant to the rational mind. It's like what old Carr was saying about the run of the cards at bridge. After a few shuffles of a multitude of cosmic factors, the laws of magic change. A sharp eye can spot the changes, but continual experimentation, of the trial-and-error sort, is necessary to keep the crude practical formulas of magic in anything like working order, especially since the basic formulas and the master-formulas have never been discovered.