The frustration which the scientist meets with when he reflects in thoroughgoing fashion on the business he has in hand is the inevitable realization that _Alles Vergängliche ist nur ein Gleichniss_, that the sphere of the finite in which he labors, though capable of indefinite extension, is forever incapable of being rounded out to a true infinity, and hence that the complete unification of the manifold (in which alone the reality-producing functions of the mind can find repose and ultimate satisfaction), can never be carried out in the manifold of juxtaposition and sequence with which, as a physical scientist, he deals. He will thus be led to face in thought the limits of what is finitely attainable, not only by him as an individual scientist, but by physical science in general. And in proportion as his spiritual nature is energetic it will then assert itself all the more resiliently after this defeat, and turn in a new direction, and towards another kind of truth, the truth which is discovered in the realm of _will_, in the sphere of intercourse with fellow human beings. The propædeutic result of science with respect to ethical personality is the training of the more complex mental faculties. The positive result following the frustration is the new turn toward the spiritual, the escape from the spell wherewith the physical world enchains the mind, the dissipating of the widespread illusion that the truths of physical science are the only kind of truth, the more determined setting of the face towards a different kind of truth. The scientist, in brief, is to travel along the paths of the finite in order to arrive and stand at the gate of the infinite. I have said that the boon of personality is gained in intercourse with others, through the influence which we exert on others. How does the scientist as a scientist spiritually affect others? The great specific service, as I have just said, which he is to render is to destroy the illusion that the material world is a finality. And it is just he, the scientist, who works most successfully in the field of physical truth who must assist the rest of us in escaping from the spell to which we are all subject. He is the one, he who more than others succeeds in unifying the manifold of juxtaposition and sequence, to whom we look to liberate others as well as himself from the deceptive belief that the reality-producing functions of the human mind can be satisfied in the temporal and spatial manifold. Not from the tyro, not from the purveyor of “popular science” can we hope to learn the profoundest lessons as to the incapacity of physical nature to appease the spirit of man. It is from the familiar friend of nature, from one more deeply read than we are in her secrets, that we are to obtain this great instruction, to receive this boon.