The development of physical science is another feature of the time plainly visible in its literature. It is needless to discuss its effect upon the material conditions of life; for that has been not only fully recognised, but its importance, for the present purpose, has been greatly exaggerated. Besides this however, the direct contributions of science to literature have been considerable, and some of them possess literary qualities rarely equalled among the scientific writings of past times. Moreover, science has so filled the minds and possessed the imagination of men that its indirect has been far greater than its direct influence. Whatever its ultimate creed may prove to be, science has certainly been in part responsible for the growth of a spirit of materialism, and has caused those who do not share that spirit to examine themselves and to remould their arguments. Science has therefore tended to depress and to give a tone of stoic resignation if not of pessimism to many who, without accepting materialistic opinions, have been affected by them. But in another way science has been an elevating and inspiring power. Its discoveries have stimulated men's minds, and have done more than anything else to rouse them from the lethargy consequent upon the apparent failure of the Revolution. They have profoundly influenced literature, both directly, and also through those philosophical and theological speculations which inevitably colour all poetry and all imaginative prose. The new facts of astronomy and geology have shaken many old theories and suggested many new ones; and the results of biological discovery have been still more striking. The transforming power upon thought of the theory of evolution may be measured by the fact that the majority even of those who dislike and deny Darwinian evolution still believe that there has been evolution of some kind. For thoughtful men, unless they are heavily fettered by preconceptions, the old view has become impossible; and no other except an evolutionary one has hitherto been even imagined. Here therefore there is a great unsettlement of popular ideas, and no little energy has been expended in fitting men's minds to the new conditions. Tractarianism, Pre-Raphaelitism, the satire, tempered with mysticism, of Carlyle, the idealistic optimism of Browning, and the creedless Christianity of Matthew Arnold, are all attempts to satisfy either the intellectual or the moral and artistic needs of modern times, and all show the influence of the scientific thought of the age.