nvolved 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.

41. Ox Yoke, 1838. USNM 148675; 1938. Edward Scoville (1813-1887) used
this ox yoke when driving an ox cart from Trumbull County, Ohio, to De
Kalb County, Indiana, in 1838. Until well after the Civil War, oxen
pulled most of the wagons going west, and this yoke is typical of all
used in the westward migration, in the North as well as in the South.
Gift of Reign Scoville, Poplar Bluff, Missouri.

[Illustration: Figure 5.--John Deere plow, one of the three plows made
by Deere in 1838. (Catalog No. 42.)]

42. Deere Plow, 1838. USNM 148904; 1938. John Deere made this plow, with
steel share and polished wrought-iron moldboard, at Grand Detour,
Illinois, in 1838. Joseph Brierton bought it and used it on his farm,
and the Deere Company obtained it in 1901. It is one of three plows made
by John Deere in 1838, and presumably it is identical to his first steel
share plow, made in 1837 at Grand Detour. Called the singing plow, it
proved especially effective in prairie country after the sod had been
broken because the earth did not adhere to the share and moldboard. The
implement could also be used as a breaking plow. Gift of Deere and
Company, Moline, Illinois.

43. Model of Sulky Plow, 1899. USNM 156653; 1940. Working model of the
Hy-Lift sulky plow invented by Niels O. Starks of