"[W]e are not at all sure that the most ancient forms of the numerals commonly known as Arabic had their origin in India. ...[T]heir forms may have been suggested by those used in Egypt, or in Eastern Persia, or in China, or on the plains of Mesopotamia. We are... in the dark as to these early steps; but as to their development in India, the approximate period of the rise of their essential feature of place value, their introduction into the Arab civilization, and their spread to the West, we have more or less definite information."