A solid bronze bar, about 38 inches long and about 1 inch square in transverse section, marked “Copper 16 oz. Tin 2½ Zinc 1 Mr. Baily’s Metal No. 1 STANDARD YARD at 62°·00 Faht. Cast in 1845 Troughton & Simms, LONDON.” and having near to each end a cylindrical hole sunk to the depth of about½ inch at the bottom of which is inserted in a smaller hole a golden plug about one-tenth of an inch in diameter with, cut upon its surface, three fine lines about one hundredth of an inch apart transverse, and two fine lines about three hundredths of an inch apart parallel, to the axis of the bar, measurement being made of the mean interval between the two plugs on their respective middle transverse lines between their respective longitudinal lines when the bar is at the temperature of 62° Fahrenheit and supported on bronze rollers placed under it in such manner as best to avoid flexure of the bar and to facilitate its free expansion and contraction from variations of temperature.