Numerology is any belief in divine, mystical or other special relationship between a number and some coinciding events. It has many systems and traditions and beliefs. Numerology and numerological divination by systems such as isopsephy were popular among early mathematicians, but are no longer considered part of mathematics and are regarded as pseudomathematics or pseudoscience by modern scientists. The term numerologist is also used derogatorily for those perceived to place excess faith in numerical patterns (and draw scientifically unsound inferences from them), even if those people do not practice traditional numerology. For example, in his 1997 book Numerology: Or What Pythagoras Wrought, mathematician Underwood Dudley uses the term to discuss practitioners of the Elliott wave principle of stock market analysis. Scientific theories are sometimes labeled "numerology" if their primary inspiration appears to be a set of patterns rather than scientific observations. This colloquial use of the term is quite common within the scientific community and it is mostly used to dismiss a theory as questionable science. The best known example of "numerology" in science involves the coincidental resemblance of certain large numbers that intrigued such eminent men as mathematical physicist Paul Dirac, mathematician Hermann Weyl and astronomer Arthur Stanley Eddington. These numerical coincidences refer to such quantities as the ratio of the age of the universe to the atomic unit of time, the number of electrons in the universe, and the difference in strengths between gravity and the electric force for the electron and proton. ("Is the Universe Fine Tuned for Us?", Stenger, V.J.,). The discovery of atomic triads (dealing with elements primarily in the same group or column of the periodic table) was considered a form of numerology, and yet ultimately led to the construction of the periodic table. Here the atomic weight of the lightest element and the heaviest are summed, and averaged, and the average is found to be very close to that of the intermediate weight element. This didn't work with every triplet in the same group, but worked often enough to allow later workers to create generalizations.