"knowing the sky, knowing your relationship with the sky, is the centre of the real answer to knowing what time it is." Tom Wujek

I did say I would write more about the development of clocks and watches. Researching this subject has been very interesting and there is so much information that I have condensed into an outline here.
The ancient Greek, Roman, Chinese and Islamic cultures all developed similar methods to mark the passage of time, oil lamps, candles, sundials, water clocks, merkhet, astrolabe. What was clear that these ancient civilisations had some amazing geniuses (or genii for the correct Latin spelling) that were able to use their knowledge of mathematics and astronomy to develop some wonderful instruments; to tell time, to be used as calendars and to track the movements of the sun, moon and stars, for use in astronomy and astrology. Sadly through the passage of time - and wars - these inventions were lost and we had to start again in the West.
Some (not all) of the greats in Time Keeping (click the name to read more) include:
Ctesibius (born in Alexandria around 300 BC) whose improvements to the water clock resulted in a time-recording device whose accuracy could not be improved on for over 1,500 years.
Hipparchus of Nicaea (born in 190 BC) who accurately recorded  the movement of the sun, moon and stars and other planets and developed trigonometry and constructed trigonometric tables and solved several problems of spherical trigonometry
Andronicus of Cyrrhus (born 100 years BC) whose Horologium (time keeping piece) called the Tower of The Winds still stands today. This public clepsydra (water clock) was driven by a stream flowing down from the Acropolis.

The Tower of the Winds, Athens.

Hypatia (born in Alexandria 370 AD) credited with creating a geared astrolabe and a planesphere.
Since ancient times as a kind of analogue computer know as an astrolabe has been used to find the time during the day or night, find the time of a celestial event such as sunrise or sunset and as a handy reference for teaching astronomy. The celestial sphere, containing  the astronomical objects - moon, sun and stars, is projected on to the plane of the astrolabe (stereographic projection). The moveable componants are lined up to correspond to the users current position and once set, the entire sky, both visible and invisible, is represented on the face of the instrument.

Watch this short animation to see a demonstration.
Download an astrolabe app for your iphone here

The Clock at Hogwarts based on the design of an Astrolabe.

There is no one person responsible for the invention of mechanical clocks rather there were developments and improvements.
Original clocks were astrological clocks based on the design of the astrolabes. The Prague Astronomical Clock or Prague Orloj is a medieval astronomical clock. It was installed in 1410, making it the third-oldest astronomical clock in the world and the oldest one still working.

Prague Orloj

So how did we get from those astrological clocks and water clocks to perpetual movement mechanical clocks, it was the development of a mechanism called an escapement.
1280-1320 saw increasing references to clocks and horologes and existing water clocks being adapted to use falling weights to power them. The release of this power was controlled by the escapement. The earliest record of an escapement being used is in medieval China - Su Song incorporated a kind of escapement in his astronomical Clock Tower of Kai Feng (1088) but it was reliant on water to power it. The date of when an escapement was first used in a clock is unknown.The first clear drawing of an escapement was by Jacopo di Dondi and his son in 1364. It is estimated that escapements were being used in mechanical clocks  in the late 1200's. 

Verge and foliot escapement from De Vick clock, built Paris, 1379, by Henri de Vick

The first mechanical clocks were no more accurate than the best water-clock accuracy. However, overtime the improvements to the design of the escapement, the method of driving the mechanism and the materials used to make them lead to very accurate time pieces. Read in detail more here.
Click here to see the British Museums wonderful animated demonstration on how an escapement works.
Salisbury Cathedral has the worlds oldest mechanical clock, installed 1386, that still strikes the hours.
Next blog how watches developed for portable clocks.
If you are really interested in the subject and curious to see old clocks and watches click here to take a look at the Antiquarian Horological Society Website.