From a nearly contemporary account:  

1670 ca. - The anchor escapement was invented, probably by William Clement. John Smith in Horological Disquisitions, 1694 says "From Holland, the fame of this invention (the pendulum) soon passed over into England where several eminent and ingenious workmen applied themselves to rectify some defects which as yet was found therein; among which that eminent and well-known artist Mr. William Clement, had at last the good fortune to give it the finishing stroke, he being indeed the real contriver of that curious kind of long pendulum, which is at this day so universally in use among us."

(from Antiquarian Horological Society's excellent timeline)

The pendulum, which Fromanteel brought from the Netherlands, was a great improvement on everything that came before, but it was now clear that a clock could keep time to seconds per week, not just minutes.  There were a couple of problems with a pendulum driven by a verge escapement. One is that it has a huge swing, as much as 15 or 20 degrees on each side, and as Huygens mathematically determined, there is a problem with timekeeping when there are huge and variable amplitudes.  One way of dealing with this is to have a small swing, as isochronous error increases as the square of the amplitude.

The verge escapement for pendulums is complicated, involving two changes in direction, and (trust me) hard to make.  It's also very inefficient, wasting a lot of the train power.

Clement's idea was simple.  The 'scape wheel turns in the same plane as the pendulum swing, and the lever which pushes the pendulum pivots at the place where the pendulum is suspended.

(from Mark Headrick's site)

Here's how it works: a tooth of the escape wheel pushes a slanted face of the lever, driving the pendulum, to which it's linked. When the tooth pushes the lever aside far enough to escape the lever continues in the same direction, driven by the momentum of the pendulum. At the same time the opposite fork of the lever interrupts the travel of the scape wheel which it actually drives backward, giving it the name, the recoil ecsapement.  The next time you see a "grandfather" clock with a seconds dial, watch the seconds hand: you'll see it reverse direction and travel backward with each tick.

Clement was admitted to the Clockmaker's Company in 1677, and became a master in 1694. The fact that he wasn't even admitted to the company until 7 years after his great invention, and became a master long after his invention had swept Europe, indicates how much of an outsider he was.

He went on to become a noted, but not particularly famous or prolific maker.  The illustration above shows the thing he was most noted for: a longcase clock with a pendulum that beat seconds and a quarter, like his tower clock.  (Note the circular glass aperture in the plinth, or lower part, of the clockcase.)  This was rare in domestic clocks, but became a fairly standard length for tower clock pendulums.  I have an English tower clock movement from 1914 with a pendulum that beats four times in five seconds.

He also made this very nice but not particularly exceptional "basket top" bracket clock.

Credit: Clement domestic clock illustrations from "Early English Clocks", Dawson, Drover, and Parkes, Baron publishing, 1982

Robert Hooke, of the Royal Society, was like that certain composer, of whom it was said that he knew a good tune when he heard one.  He tried to use his establishment credentials to claim credit for this invention, which becomes important in a future article, when he's not believed when he claims an invention that he actually may have made. A google search will show pages and pages of references to Hooke's invention of the anchor escapement.  As we have recently seen, saying something false over and over again doesn't make it any more true.  

In any event, this invention was important because it made possible long pendulum, short amplitude, pendulum clocks which kept time to 10 seconds a week.  An English longcase clock from the end of the 17th century will keep time to modern domestic standards.  In fact, in the age of constant temperature interiors, they probably keep better time than when they were new.

Next time: Edward East, and the golden age of English horology, part one.

Previously:

Monastic alarms and the beginnings of clockmaking
De Dondi's remarkable astrarium
Early tower clocks
Gothic iron clocks
Rennaisance clocks
Early english lantern clocks
Huygens and the pendulum
Fromanteel's English pendulum clocks
Huygens in Paris