They crossed the Thames by swimming, or in small boats which they constructed of wicker- work and covered with skins. Their towns were protected by stockades and morasses, and consisted of huts in which a single aperture served the purposes of door and window.
Imagine the feelings with which one of these ancient Britons would contemplate modern London. He would see the same sky and sea and river, and would meet men of the same stature as himself, but all else would appear to have undergone a magical transformation.
What were in his time desolate mud banks are now defended against the river by embankments of solid masonry, beyond which, on either side, he would see the churches, railway stations, factories, hotels, and private dwellings of a mighty city.
He would wonder at the great bridges with which the broad river is spanned, and at the iron ships coming in from the sea against wind and tide without the help of sail or oar. Wherever he turned he would be struck dumb by the power over Nature exercised by human beings closely resembling himself, except for the one material difference of superior knowledge.
For the superior power which raises the modern civilized man so far above his barbarous contemporaries and predecessors, is all derived from increase of knowledge. By learning the properties of the magnetic needle, the mariner has acquired the power of traversing the ocean in the darkest night, when there are no stars visible.
Knowledge of the properties of saltpeter and dynamite enables the engineer to cut a path through the solid rock, so that the locomotive may pass under the Himalayas or climb the mountain barrier of the Ghats.
By studying the properties of steam, modern inventors have learned to construct engines by means of which distant parts of the earth have been brought into close communion with each other; and knowledge of electricity is likely to produce in the future still greater progress in the same direction.
Object-lessons illustrating the power acquired by knowledge crowd in upon the eyes in boundless profusion, as we pass through the thickly populated centers of modern civilization, and see how human industry has transformed the face of Nature.
All the changes that man has effected by working upon Nature are due to knowledge; and, if the knowledge now possessed by civilized men were suddenly lost, the whole world would relapse into barbarism.
Fortunately, knowledge has fortified herself against the possibility of such a catastrophe by the invention of the art of printing, which secures future generations against the danger of losing the result of the scientific discoveries of their predecessors.