Early forms of linear motion bearings consisted of a row of wooden rods placed beneath a row of pry bars. Modern linear bearings operate on the same principle, though balls sometimes replace rollers. The simplest rotating bearing is the sleeve bearing, merely a bushing sandwiched between a wheel and axle. This design was later superseded by rolling bearings, which replace the bushing with numerous cylindrical rollers—each rolling element functioning like an individual wheel. An early example of ball bearings was discovered on an ancient Roman ship built around 40 BC at Lake Nemi, Italy: a wooden ball bearing used to support a rotating tabletop. Leonardo da Vinci is said to have described a ball bearing around 1500. Among the various immature factors of ball bearings, a significant issue was the collision between balls, causing additional friction. However, this phenomenon could be prevented by placing the balls into individual cages. In the 17th century, Galileo provided the earliest description of ball bearings with “caged balls.” By the late 17th century, English engineer C. Vallourain designed and manufactured ball bearings, testing them on postal carriages. British inventor P. Worth later patented the ball bearing. The earliest practical rolling bearing with a cage was invented by clockmaker John Harrison in 1760 for his H3 chronometer. At the end of the 18th century, German engineer H.R. Hertz published a paper on contact stresses in ball bearings. Building upon Hertz's achievements, German engineer R. Striebeck, Swedish engineer A. Pärmgrén, and others conducted extensive experiments, contributing significantly to the development of rolling bearing design theory and fatigue life calculations. Subsequently, N.P. Petrov of Russia applied Newton's law of viscosity to calculate bearing friction. The first patent for ball grooves was obtained by Philip Vaughan of Carmarthen in 1794.