The late Professor Robert H. Thurston, of Cornell University, once said:--“Methods of planning scientific investigation involve, first, the precise definition of the problem to be solved; secondly, they include the ascertainment of ‘the state of the art,’ as the engineer would say, the revision of earlier work in the same and related fields, and the endeavor to bring all available knowledge into relation with the particular case in hand; then the investigator seeks information which will permit him, if possible, to frame some theory or hypothesis regarding the system into which he proposes to carry his experiment, his studies, and his logical work, such as will serve him as a guide in directing his work most effectively. “The empirical, the imaginative, and even the guess work systems, or perhaps lack of system, have their place in scientific research. The dim Titanic figure of Copernicus seems to rear itself out of the dull flats around it, pierces with its head the mists that overshadow them and catches the first glimpse of the rising sun. But first Copernicus made a shrewd guess, and then followed with mathematical work and confirmation. . . . Kepler, also, was strong almost beyond competition in speculative subtlety and innate mathematical perception. . . . For nineteen years he guessed at the solution of a well-defined problem, finding his speculation wrong every time, until at last a final trial of a last hypothesis gave rise to deductions confirmed by observation. His first guess was that the orbits of the planets were circular, next that they were oval, and last that they were elliptical.” Pascal, great in what he knew, was great also in what he was. Walter Pater thus depicts his powers:--“Hidden under the apparent exactions of his favorite studies, imagination, even in them, played a large part. Physics, mathematics, were with him largely matters of intuition, anticipation, precocious discovery, short cuts, superb guessing. It was the inventive element in his work, and his way of painting things that surprised those most able to judge. He might have discovered the mathematical sciences for himself, it is alleged, had his father, as he once had a mind to do, withheld him from instruction in them.” No such gift of intuition as that displayed by Pascal fell to the lot of Buffon, who tells us:--“Invention depends on patience. Contemplate your subject long. It will gradually unfold itself, till an electric spark convulses the brain for a moment.”