A period of this nature is found in his analysis of the third and last great illusion, which holds that happiness will be realizable in the progressing evolution of the world. The chapter in which this subject is treated is one of the most masterly in his entire work, and as such is well deserving of careful examination. First, it may be explained that to the student of modern science the history of the world is that of a continuous and immense development. The union of photometry and spectral analysis enables him to follow the evolution of other planets, while chemistry and mineralogy teach him something of the earth's own story before it cooled its outer crust. Biology discloses the evolution of the vegetable and animal kingdom; archæology, with some assistance from other sources, throws an intelligible light over the prehistoric development of man, while history brings with it the reverberation of the ordered march of civilization, and points at the same time to larger and grander perspectives. It is not hard, then, to be convinced of the reality of progress; the difficulty lies in the inability to present it to one's self in a thoroughly unselfish manner. From an egoist point of view, man--and by man is meant he who has succeeded in divesting himself of the two illusions just considered--would condemn life not only as a useless possession, but as an affliction. He has, however, Hartmann tells him, a rôle to fill under the providential direction of the Unconscious, which, in conformity with the plan of absolute wisdom, draws the world on to a beneficent end, and this rôle exacts that he shall take interest in, and joyously sacrifice himself to life. If he does otherwise, his loss prevents no suffering to society, on the contrary, it augments the general discomfort by the length of time which is needed to replace a useful member. Man may not, then, as Schopenhauer recommended, assist as a passive spectator of life; on the contrary, he must ceaselessly act, work, and produce, and associate himself without regret in the economic and intellectual development of society; or, in other words, he must lend his aid to the attainment of the supreme goal of the evolution of the universe, for that there is a goal it is as impossible to doubt as it is unreasonable to suppose that the world's one end and aim is to turn on its orbit and enjoy the varied spectacle of pain. And yet, what is this goal to which all nature tends? According to a theory which nowadays is very frequently expressed, it is the attainment of universal happiness through gradual advancement and progress.