There are scientific problems and literary tasks which can be worked out once for all, or which, at least, admit of final solution, to the lasting fame of him that finds that solution, as well as to the permanent benefit of civilized man. There are others, more numerous and far more interesting, which are ever being solved, finally perhaps in the opinion of the discoverer, and even of his generation, but ever arising again, and offering fresh difficulties and fresh attractions to other minds and to newer generations of men...