36. Half-Bushel Measure, about 1829. USNM 137960; 1936. Made and used by William Heiss on his farm in Lagrange County, Indiana, about 1829. Probably used in local barter and trade in such items as beans, corn, and seeds for various crops. Loaned by E. W. Heiss, Washington, D. C. [Illustration: Figure 4.--Cotton planter, about 1895. (Catalog No. 37.)] 37. Wooden Drum Cotton Planter, about 1895. USNM 14557; 1937. All wood except for a duckbill furrow opener in front and two duckbill row coverers in the rear, both made of metal. The drum of soft wood measures 20 inches in diameter and 13 inches wide. About the center of the drum is a wooden, metal-rimmed wheel which ran down the furrow, keeping the seeder on course. Near the wheel, and all around the drum, are 13 evenly spaced holes through which the cotton seeds fell into the furrow as the drum revolved. No counting or tripping mechanism was involved, so the device undoubtedly wasted seed. A mule or a horse pulled the planter and the farmer walked behind it. James Nelson of Greenwood, South Carolina, made this planter about 1895. Gift of Ruben F. Vaughn, Honea Path, South Carolina. 38. Cast-Iron Plow, 1854. USNM 150396; 1938. A cast-iron plow made by Stephen McCormick of Fauquier County, Virginia, in 1854. The plow embodies features covered by patents issued to Stephen McCormick on February 3, 1819, January 28, 1826, and December 1, 1837. Plows of this type, made chiefly between 1826 and 1850, involved interchangeable parts. The first patent precedes that of Jethro Wood by seven months, but the principle of interchangeable parts had been worked out and patented as early as 1813. Gift of Leander McCormick-Goodhart, Silver Spring, Md. 39. Mehring's Milking Machine, 1884. USNM 148530; 1938. Original working model of a hand-powered milking machine built by William M. Mehring in 1884. Mehring subsequently improved and patented the machine in 1892. The improved machine did not work well because it created continuous suction for the length of the stroke. The successful application of intermittent suction, necessary so as not to injure the cow, was worked out in Scotland in 1902. Gift of Mrs. Bessie D. Mehring, Keymar, Maryland. 40. Hand-Powered Milking Machine, 1892. USNM 148530; 1938. Practical hand-pump milking machine designed and built in 1892 by William M. Mehring, who was granted patent 488282 on December 28, 1892. This milker, which injured cows when used rapidly, represents an effort to solve the problem of machine milking, although the use of human power also limited its usefulness. Gift of Mrs. Bessie D. Mehring, Keymar, Maryland.