The struggle for every second!
When Kepler (an astronomer, 1571 - 1630) showed, that the movement of the celestian bodies followed mathematical laws, it was necessary to confirm the correctness of this theory through observing the planetary orbit. Such an observation can for instant mean, that the location of a planet in the sky is determined at a certain time. The more accurate the measuring is made, the more meaningful it is and the easier inconsistencies are found of the theory that was to be investigated. The demand for accurate measurings was increase, when Isaac Newton (physican & mathematic, 1643 - 1727) realised, that the gravity of celestian bodies had an influrence on the course of the planets and therefore the planets did not stand in the sky in the way Kepler wanted them to be. The Kepler laws now extended by Newton, meant to be confirmed of course. And that was done through observation. It meant, that good clocks were needed - the more accurate, the better.
Where does the second come from in the 17th century?
The "primary measure" of the time was found by the earth itself. It was assumed, that the earth turned at a constant speed. The passing stars in the sky at night resulting from this was almost the most monotary event that one could imagine. More monotary than any clock that existed those says and that still did not existed until 1930. To determine the time for a rotation, the starry sky had to be observed. For instant, they chose a star, fixed it exactly, let the earth make a rotation until the star was at its position again and the time was taken between the two events. That was (and still is of course) one sidereal day. At the time of the observation the time was given pretty accurately - up to 0.1 sec. exact, for sure. But what happened, when it was cloudy, when an observation was impossible? Clocks were needed to get over these periods; accurate clocks.
The solution
At exactly that time when the requirements for clocks were getting more and more important, George Graham presented the solution. Let's go into it a little more: A freely swinging pendulum, swings from side to side with a tremendous, constant, periodic durance. But only, if the amplitude remains constant. Apparently, one pendulum by itself can not fulfil these requirements. At some time it will just stop. That is the reason why you get an escapement. It gives the pendulum only as much energy as it needs.
But this energy supply disturbs the pendulum and the escapement did not know, when to release the energy. Therefore most escapements are in constant contact with the pendulum and get told exactly, when to give up energy. The "in contact" and "giving up energy" has to be done with a monotonous regularity, if the pendulum is suppose to divide the time "exactly". And that is the very requirement the Graham escapement fulfils - in an excellent way.
If you have a look at the animation above, you will see the harmony of the movements. There is no back and forth like in many other escapements (i.e. verge escapement). There is no sudden speed-up or brutal halt of some prefabricated parts. It seems as though everything works together and not against each other and that is where the value lies of this construction. One could say, that any hectic in the escapement, only costs energy. This one here does not spread any hectic in its phases of movement. Furthermore, there is the simplicity of this construction. It allows the escapement to be very accurately built with simple means. Now that is not bad - is it! |
