Descartes, the essential Enlightenment rationalist, was responsive to his “...call of the Spirit...” Napier the inventor of logarithms wrote an exegetical commentary on the Book of Revelations. The mathematician and physicist, Pascal, believing that contact with a religious relic had cured his terminally ill sister, wrote long tracks about whether or not the Devil could work miracles. The great mathematician, Cauchy, was known for his persistent efforts to convert fellow mathematicians to Roman Catholicism. Gauss, who was not particularly religious, said that a difficult to prove theorem did not result from hard work but “...the grace of God.” In letters between Liebniz, who along with Newton was the inventor of calculus, and a member of the family of great mathematicians, John Bernoulli, used scriptural quotations and biblical diagrams as part of their theoretical correspondence. Perhaps the greatest mathematician of the 18" Century (or ever), Euler, in his Letters to a German Princess, discussed the functional characteristics of spirits and the connections between body and soul. Bell said Euler “...never discarded a particle of his Calvinist faith.” It was to the working out of a law of mechanics called “the principle of least action” that Ernst Mach attributed the beginning of the separation of physical mechanics from formal theology. The flavor of this change is captured in his 1893 The Science of Mechanics that stimulated Bridgeman’s 1936 more formal philosophical analyses of physical theory, from a position that came to be called operationalism: the restriction of physical concepts to those definable in terms of the experimental operations required to demonstrate or prove them. Mach said that these events marked the move of formal metaphysical thinking about mechanics and the physical sciences more generally into the personal and private realm of belief and meaning. Maupertuis, an eccentric friend of Frederick the Great and president of the Berlin Academy, p