Christiaan Huygens discoveries
In 1654, his attention was directed to the improvement of the telescope. Together with his brother, Christian Huygens devised a new and better way of grinding and polishing lenses. As a result of these improvements, Huygens was able during 1655 and 1656 to resolve numerous astronomical questions of the day including the fact that Saturn's rings were made of rocks and the presence of Titan.
Pendulum Clock and Watches
In 1656, Huygens invented the first pendulum clock, as described in his 1658 article "Horologium". The time-pieces previously in use had been balance-clocks, Chris Huygens' pendulum clock was regulated by a mechanism with a "natural" period of oscillation and had an error of less than 1 minute a day, the first time such accuracy had been achieved. His later refinements reduced his clock's errors to less than 10 seconds a day
Around 1675, Huygens developed the balance wheel and spring assembly, still found in some of today's wrist watches. This improvement allowed 17th century watches to keep time to 10 minutes a day. Watches or portable clocks had been invented early in the sixteenth century, however, they were clumsy and unreliable, being driven by a main spring and regulated by a conical pulley and verge escapement. The first watch whose motion was regulated by a balance spring was made in Paris under Huygens' directions, which he gave as a gift to Louis XIV the King of France.
The increasing intolerance of the French Catholics for his science led to Christian Huygens' return to Holland in 1681. He then devoted himself to the construction of lenses of enormous focal length. Three telescopes he made with of focal lengths of 123 feet, 180 feet, and 210 feet, were given to the Royal Society of London where they remained. It was about this time that Christian Huygens discovered the achromatic eye-piece (for a telescope) which is named after him.