How the foot, our commonest measure, has descended to us is an interesting story. The oldest known standard of length, the cubit, was the distance between the point of a man’s elbow and the tip of his middle finger. In Egypt the ordinary cubit was 18.24 inches, and the royal cubit, 20.67 inches. A royal cubit in hard wood, perfectly preserved, was discovered among the ruins of Memphis early in the nineteenth century. It bears the date of the reign of Horus, who is believed to have become King of Egypt about 1657 B. C. The Greeks adopted a foot, equal to two-thirds of the ordinary Egyptian cubit, as their standard of length. This measure, 12.16 inches, was introduced into Italy, where it was divided into twelfths or inches according to the Roman duodecimal system, thence to find its way throughout Europe. Units equally important with the cubit were from of old derived from the finger and the fingers joined. The breadth of the forefinger at the middle part of its first joint became the _digit_; four digits were taken as a _palm_, or hand-breadth, used to this day in measuring horses. Another ancient unit, not yet obsolete, the _pace_, is forty digits; while the _fathom_, still employed, is ninety-six digits, as spaced by the extended arms from the finger tips. The cubit is twenty-four digits, and the foot is sixteen digits. Thus centuries ago were laid the foundations of the measurement of space as an art. A definite part of the human body was adopted as a standard of length, and copied on rods of wood and slabs of stone. Divisors and multiples, in whole numbers, were derived from that standard for convenience in measuring lines comparatively long or short. And yet in practice, even as late as a century ago, much remained faulty. Standards varied from nation to nation, and from district to district. Carelessness in copying yard-measures, the wear and tear suffered by lengths of wood or metal, the neglect to take into account perturbing effects of varying temperatures on the materials employed, all constrained men of science to seek a standard of measurement upon which the civilized world could unite, and which might be safeguarded against inaccuracy. The Metric System.