Periodic table (detailed cells)
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev invented the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
Beda Venerabilis' Easter cycle
In the year 616 an anonymous scholar extended Dionysius Exiguus' Easter table to an Easter table covering the years 532 up to and including 721. Dionysius' table was published in 525 and only a century later accepted by the church of Rome, which from the third century up till then had given preference to go on using her own, relatively inadequate, Easter tables. From about the middle of the seventh century all controversy between Alexandria and Rome as to the correct date of Easter ceased, as both churches were now using identical tables.