RICHARD FOSTER is captivated by a time machine that graces one of Yorkshire's great stately homes.

THE steady click-clock marking time in the Billiard Room at Nostell Priory, near Wakefield, is the sound of history. It comes from a longcase clock made in 1717 by John Harrison, the gifted son of the estate carpenter.

The mechanism is almost entirely made of wood, with the movement, frame and wheels in oak, the pendulum in mahogany, and the spindles and pinions in boxwood.

Harrison was born in the nearby village of Foulby and, after learning his trade in Yorkshire, became famous for inventing the first timekeeper accurate enough to determine longitude at sea.

After a long struggle, he received £20,000 - "a king's ransom" then - from the British Government for solving a problem of navigation many thought to be insoluble.

It was thanks to Harrison's astonishing work that Britain's seamen were able to safely navigate the world's oceans and carve out the British Empire.

So it was a privilege for me to be get up close to see the ingenious workings of Harrison's magnificent clock, still keeping good time, nearly 300 years after it was made.

Nostell Priory was built by James Paine on the site of a 12th century medieval priory dedicated to St Oswald for Sir Rowland Winn, 4th Baronet, in 1733. Later Robert Adam was commissioned to complete the state rooms, which are among the finest examples of his interiors.

The priory houses one of England's best collections of Chippendale furniture, designed especially for the house by the great cabinetmaker.

Other treasures include a remarkable 18th-century doll's house complete with its original fittings and Chippendale-style furniture, and an outstanding art collection with works by Pieter Brueghel the Younger and Angelica Kauffmann, a feminist icon who became one of only two female founder-members of the Royal Academy.

In the grounds are delightful lakeside walks with a stunning collection of rhododendrons and azaleas in late spring.

This year Nostell Priory celebrates 350 years as the Winn family's home and 50 years in the care of the National Trust. To mark the occasion the priory's parkland has been opened to the public for the first time - thanks to a Heritage Lottery Fund grant awarded in November 2002 that enabled the National Trust to acquire the land.

Nostell Priory is also taking part in Maids And Mistresses, an ambitious series of linked exhibitions in seven of Yorkshire's greatest country houses, the others being Brodsworth Hall, Doncaster; Burton Constable Hall, near Hull; Castle Howard, near Malton; Harewood House, Lotherton Hall, and Temple Newsam, all near Leeds.

Maid And Mistresses highlights the lives and achievements of the female occupants of these stately homes over the last 300 years.

One of Nostell Priory's most colourful characters was Esther Winn who eloped to Manchester with a lowly baker, John Williamson, in 1792.

She obviously wanted to get away from her Swiss mother, Sabine, who became very stout after the death of her husband, the 5th Baronet, and was pushed about the house in a quaint big-wheeled chair.

Esther and John had three children before he died in 1799, followed by his grieving widow four years later. She was only 35.

The Parish Church of St Michael and Our Lady, Wragby, near the entrance to Nostell Priory, is also well worth a look, with its stunning collection of antique Swiss stained glass.

Fact File:

Opening hours: House, 1pm to 5pm, grounds 11am to 6pm, Wednesday to Sunday.

Admission: Adult £5, child £2.50, family £12.50. Grounds only, £2.50, child £1.20.

Refreshments: Stables Tearoom. Kiosk in car park. Picnics welcome in car park and on the vista parkland in front of the house.

Location: Nostell Priory is on the A638, five miles south-east of Wakefield towards Doncaster.

Updated: 10:57 Saturday, July 17, 2004