In contrast, there were no advances in roller technology during the Middle Ages. While the use of such objects remains unknown, it is strong evidence that China was also investigating the advantages of rolling over sliding. Annular bronze objects which contained a number of internal compartments have been found that date back to 100 B.C. The Chinese also displayed use of rolling elements. Other archeological finds show the use of rudimentary thrust bearings (bearings that can handle both an axial and radial load), as well as objects who’s uses can only be speculated. Rollers were commonly used when moving large stone columns for architecture purposes. The Romans showed clear evidence of using rollers as early as 900 B.C. While prehistoric civilizations show no use of rollers to move heavy objects, early civilizations displayed a clear knowledge of the advantages of rolling as opposed to sliding. While da Vinci worked on improving ball bearings in the late 15 th century, their appearance in history dates back to ancient times with societies including the Romans and Chinese. Even when these errors were corrected by the Gregorian calendar, many orthodox churches still choose to continue using the Julian calendar even through to today. Despite these flaws, this calendar was still the most accurate measurement of time in the Roman empire and the Western world. Additionally, the first few decades of the Julian calendar were run under a calculation error, causing a leap year every third year, which only exasperated the problem. This caused important holidays and religious events, such as Easter, to fall several days off of an equinox or solstice. However, this is too often for leap years to occur, and even this more accurate calendar fell out of sync with the Earth’s solar orbit. Every fourth year is a leap year, with a leap day added to the last month of the year, Februarius. The common year of the Julian calendar is 365 days divided into 12 months. Caesar, frustrated with the inaccuracy of the Roman lunar calendar, called upon Sosigenes, an Alexandrian astronomer, to create a solar calendar, based on the Earth’s revolution around the Sun, about 365.242 days. The Julian Calendar replaced the Roman Calendar in 45 BCE on the order of Julius Caesar.
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