A difference like this, once set up, implies thereafter innumerable other differences which naturally flow from it. Some of them are extremely remote and derivative. Take, for example, the case of writing and printing. Why do these run from left to right? At first sight such a practice seems clearly contrary to the instinctive tendency I noticed above--the tendency to draw from right to left, in accordance with the natural sweep of the hand and arm. And, indeed, it is a fact that all early writing habitually took the opposite direction from that which is now universal in western countries. Every schoolboy knows, for instance (or at least he would if he came up to the proper Macaulay standard), that Hebrew is written from right to left, and that each book begins at the wrong cover. The reason is that words, and letters, and hieroglyphics were originally carved, scratched, or incised, instead of being written with coloured ink, and the hand was thus allowed to follow its natural bent, and to proceed, as we all do in naive drawing, with a free curve from the right leftward. Nevertheless, the very same fact--that we use the right hand alone in writing--made the letters run the opposite way in the end; and the change was due to the use of ink and other pigments for staining papyrus, parchment, or paper. If the hand in this case moved from right to left it would of course smear what it had already written; and to prevent such untidy smudging of the words, the order of writing was reversed from left rightward. The use of wax tablets also, no doubt, helped forward the revolution, for in this case, too, the hand would cover and rub out the words written. The strict dependence of writing, indeed, upon the material employed is nowhere better shown than in the case of the Assyrian cuneiform inscriptions. The ordinary substitute for cream-laid note in the Euphrates valley in its palmy days was a clay or terra-cotta tablet, on which the words to be recorded--usually a deed of sale or something of the sort--were impressed while it was wet and then baked in, solid. And the method of impressing them was very simple; the workman merely pressed the end of his graver or wedge into the moist clay, thus giving rise to triangular marks which were arranged in the shapes of various letters. When alabaster, or any other hard material, was substituted for clay, the sculptor imitated these natural dabs or triangular imprints; and that was the origin of those mysterious and very learned-looking cuneiforms. This, I admit, is a palpable digression; but inasmuch as it throws an indirect light on the simple reasons which sometimes bring about great results, I hold it not wholly alien to the present serious philosophical inquiry.