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Jewels - Bearings that are used in a watch movement to reduce friction.  They are usually synthetic sapphires or rubies.  They help to maintain the watch's lubrication with far less friction than metal.

Julian Calendar - Julius Caesar introduced a calendar with 12 months and 365 days. Previously the calendar had 10 months of 30 days each. The Julian calendar introduced the "leap year" stating that a day would be added to the calendar every 4 years. That is required because there are roughly 365.25 days in a year (not 365) and to catch up to the extra 1/4 day per year a whole day was added every 4 years.