The first reliable calculation of the speed of sound was made at Upminster.

Nowadays, scientists specialise in minute research. But, 300 years ago, they were interested in anything and everything, designing their experiments as they went along.

The Reverend William Derham, rector of Upminster from 1689 to 1735, was a friend of Sir Isaac Newton, who discovered gravity, and Dr Halley, the expert on comets.

He played with clocks, barometers and magnets, and investigated strange phenomena.

A Hornchurch woman gave birth to a baby that had reportedly cried while still in the womb, Derham rode across the Ingrebourne to inspect mother and child. Both were doing well, but whether the story was true he couldn't tell.

Upminster's parish church was infested with destructive death-watch beetle. Derham put one in a box to study its habits. Surprise – it ate its way out!

His most celebrated project, between 1705 and 1707, was an attempt to measure the speed of sound. Two great pioneer scientists, Newton and Robert Boyle of Boyle's Law, had failed to crack the problem.

From the tower of St Laurence's church, Derham could see prominent buildings, such as his friend Mr Barrett's mansion, Belhus, at Aveley, and the windmill that stood on Shepherd's Hill to the north.

He persuaded his neighbours to fire guns at set times from local landmarks. For instance, on February 3, 1705, he sent his servant to Belhus with a request to have guns fired at 6 o'clock that evening, the first towards Upminster, the second up in the air, the third "fromwards" (backwards). There was no standard time in 1705, so the servant showed Mr Barrett the rector's pocket watch "by which you may see when I account it 6 at Upminster".

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Perched in his church tower, Derham used a telescope to detect the flash when the gun was fired. He was also equipped with a clock that ticked in half-seconds, operated by a lever, which he could push the moment he spotted the flash without looking at it. When the rumble of gunfire reached him, he pressed the lever again for a timing.

Because sound takes only about five seconds to travel a mile, the half-second clock was vital. Unfortunately, Derham was so excited when he spotted the first gun from Aveley that he jogged the clock and lost his calculation. Mr Barrett obligingly repeated the experiment a few days later. The rector lit a bonfire to show he'd received the signal.

The experiment was so important that Derham published the results in Latin, still Europe's international scientific language: North Ockendon and South Weald appear as Ockendon Borealis and Weald Australis.

Results included four and a half seconds from St Andrew's at Hornchurch, 11 seconds from Shepherd's Hill windmill and 17 seconds from Rainham church. The furthest guns observed by Derham were fired by the Army at Blackheath, twelve and a half miles away.

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Distances were measured by triangulation. Draw a baseline 100 feet long at Upminster, and measure the angles at both ends of the lines leading to the spire of St Andrew's. Then draw a much smaller triangle with the same angles, but a twelve-inch baseline, and measure at right angles to the apex. Multiply by 100, and you have the precise distance from Upminster to Hornchurch.

Since light travels at 186,000 miles a second, the 3.6 miles covered by a flash arriving from Rainham could be ignored.

Combining all his results, Derham calculated the speed of sound at 768 mph.

When jet planes were developed in the 1940s, Derham's experiments acquired practical importance. Aircraft breaking the sound barrier created sonic booms, which could smash windows: calculating the exact speed of sound was not just a theoretical exercise.

Physicists were impressed by Derham's work. His results were slightly amended: with normal air pressure at 15 degrees Celsius, the speed of sound is 760 mph. Derham was out by just 8 mph. Not bad for 1705!