History of chemistry
An important breakthrough in making sense of the list of known chemical elements (as well as in understanding the internal structure of atoms) was Dmitri Mendeleev's development of the first modern periodic table, or the periodic classification of the elements. Mendeleev, a Russian chemist, felt that there was some type of order to the elements and he spent more than thirteen years of his life collecting data and assembling the concept, initially with the idea of resolving some of the disorder in the field for his students. Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups of elements. Mendeleev's law allowed him to build up a systematic periodic table of all the 66 elements then known based on atomic mass, which he published in "Principles of Chemistry" in 1869. His first Periodic Table was compiled on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties.
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.