Saturday, 29 July 2017

Colonel Péchot – it’s personal

Prosper Péchot was first and foremost an artillery office. Before he developed his system of 60cm railways, he invented an automated range-finder for gunnery. It was in fact an analogue computer!
Prosper Péchot 1849-1928 Photo courtesy of Raymond Péchot
The description given to the French Patent Office described it as ‘a device’ which can be added to existing range-finders ‘to find the range automatically’. The device could be fitted to cylindrical rangefinders or ones consisting of steel ribbons. The machine à diviser (range-finder) which Péchot intended to improve was one invented by a M. Guyenot which depended on a steel ribbon. In the field, this proved inflexible as the range could only be found to certain arbitrary measurements. The drawing accompanying Péchot’s patent application shows an impressive array of cogs and levers which attached to the existing range-finder. One thinks of the Babbage Difference Engine. 
Almost programmable. One detail of sketch which accompanied Péchot's patent application

Another detail Péchot's analogue computer. The handle shown above turns the gear. Both pictures courtesy of Raymond Péchot
Wouldn’t it be wonderful if one was to be constructed! The patent refers to discussions held in 1879-80 when Péchot was at Bourges. The reference is
no: 777The patent was lodged on March 7th 1880 at the Prefecture of Cher.
The full story is in my book ‘Colonel Péchot: Tracks to the Trenches’ chapter Two.

There are parallels between the story of Prosper Péchot and some of my own family.  My great-great grandfather, David Davidson, 1811-1890 invented a related device, a collimating gun sight.
He had always been interested in ordnance. As a boy, he invented a crossbow of ‘peculiar and novel construction’ from which he could shoot pellets with precision. His targets were sparrows, needed as food for his pet sparrow-hawk. He used the top of the family’s weather-cock for target practice; the workman sent to repair it looked down on the young shot. He favoured him with a look and a shake of the head but did not tell. He also ‘peppered’ the monkeys of the local travelling circus (Wombwell’s Menagerie). Being used to projectiles, the monkeys were neither hurt nor surprised  but disappointed to find that Davidson’s missiles were not edible.
When he was fourteen, his target was Sandy the gardener. Sandy was seventy yards away and foolishly said to young Davidson ‘I’ll wager you’ll no hit me’ This was a tempting challenge and he ‘hit him in a safe place’ – I assume his bottom. Sandy admitted it was quite sore. Such merry japes continued until he was packed off to India in 1827 to become a servant of the Honourable East India Company.
The Indians he met were a good influence on him. For the rest of his life, he held them in respect. He developed his original ideas, first being a sort of blow-pipe to which he attached his design of telescopic sight and indulged his love of hunting. In those days, the only good tiger or cobra was a dead one – sad but true. 
In 1839, he wrote a paper entitled ‘Rifled Cannon’ which was brought to the attention of the Duke of Wellington. The crusty old war-horse wrote back a lengthy criticism to the effect that rifled cannon were an impossibility. His paper was better received by the Royal Society when it was read in Edinburgh by Professor Piazzi Smyth.
Years later, projectiles were made with copper studs which could engage in the rifling. Sir David claimed that ‘the principle was the same’ and that he had been justified! Pic p215
David Davidson's innovation. At the top is a cross-section of the gun barrel showing grooves in the gun barrel. Below are sketches of the shell shown in crosssection and lengthways. In the system that was subsequently adopted, copper studs rather than continuous bars were used. Picture courtesy of the Davidson family
An early version of a telescopic sight was shown at The Great Exhibition of 1851.
Soon, he and his friend Professor Piazzi Smyth were working on improvements. When the Crimean War was in progress and the British gunners hit a problem with Sebastopol. They could spend a whole day pounding at the defences with their guns. While they rested at night, the Russians went and repaired the damage so that ‘in the morning the assaulting party … instead of a practical breach … were faced by fresh (enemy artillery)’.
Davidson’s idea was to register the British guns so that they could keep up their fire with equal precision at night. His invention was tried out at Woolwich but the siege of Sebastopol was over before they could be used. He had the comfort of being told by Sir J.H. Lefroy of the United Service Institution that ‘if such as siege as Sebastopol were to occur again, (he) had no doubt this instrument would be deployed’
In practice, the recoil of heavy artillery would upset careful calculations but this was not an end to his Collimating Telescope. In 1858, he was invited to fit an improved version of his new Collimator to a Whitworth rifle. He heard nothing more. Later a friend researched the matter and found that 100 Whitworth rifles fitted with his sight ran the blockade and were used by the Confederate side, from Shiloh to Beatonside.
So armed, the Confederate snipers were deadly. They could fire to a range of 2200 yards (1.98 kilometres). The new sight was also used by the other side. A small body of Federal snipers equipped with the new gun-sight kept a Confederate battery silent for twenty days. When the position was taken, they found 50 gunners had been killed, chiefly by head shots, from a distance of 1100 yards (0.99km). The heads of the targets could not be seen with the naked eye.
The new sight was not adopted in Britain. Davidson described the blunders of the testing committee and ended with: ‘Inventors outside the dominant clique have a poor chance of fairplay’.
Davidson’s invention, was based on a device used by astronomers. It needed a small lantern and came in a carrying case. When setting up, the carry-case could be weighted (Davidson recommended the use of lead shot) and was then used as a platform for the device. Where two sets of cross-hairs intersected, as shown in his diagram, the aim was registered.

It could be adapted for field mortars, he commented.
Davidson returned  from India in 1850. He and his wife lived in Edinburgh but later on, they had a summer residence in Aboyne. They raised a family of ten children, five boys, five girls.
In 1880, he published his ‘Memories of a long life’. The book has recently been relaunched in the USA.

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