Wednesday, 23 January 2013

Father Geoffrey's journey

Once upon a time, five hundred years ago, there was a clergyman in a village church in Devon who had a problem.  As part of his duties as priest, he needed to hear the confessions of his parishioners, when he would hear their sins and grant them forgiveness.  In other village churches, the people would come to the church and make their confessions there.  But in the parish of Bere Ferrers, on a peninsula between the rivers Tavy and Tamar in south-west Devon, the parishioners were scattered in their farms and there were several silver mines.  How could he plan to hear confessions?  Farming went alongside mining; some people did both.  As he considered his parish, this priest (let's call him Father Geoffrey because that sounds suitably medieval) had two thoughts about his problem.

First, if he told the miners to come to the church for confession, they would lose at least a day's production at the mine - one day for the return trip to the church and a little more time to catch up on the effects of a day away from the mine.  And the king needed the silver.  So did the church, which derived part of its income from the mines.

Second, if he went to the miners (against the well-established customs in other parishes) he could visit all the outlying farms, visit the sick, and enjoy the hospitality of some of the farmers.  This might be pleasant.  He could have a tour of the parish as well as doing his church duty.

Father Geoffrey was not only thoughtful, he was educated; in fifteenth century Devon, there were not many people who could read and write.   He wrote down in a list the names of the forty-eight households or mines in the parish.  And he drew a simple map of these forty-eight.  And one day, he rearranged his list to make a route around those places, making sure that he never doubled-back on himself.  Then he divided the list into a succession of days, to balance the number of confessions to be heard each day and (privately) to give himself a nice place to stay overnight.  His choice of visiting would have more benefits than summoning his parishioners to the church.

So, one day, a fortnight before Easter, Father Geoffrey made his tour of the parish.  It was a great success.  His parishioners enjoyed seeing him.  Bere Ferrers in spring is a beautiful place.  He returned to his home tired, well-fed and happy, ready for the celebration of Easter.

So successful was his trip, that he repeated it the next year.  And, to remind himself of the route, he wrote it down.  His church owned several manuscripts (this was, of course, before the first printed books).  He recorded his journey on the back of one of the church manuscripts, so he could do the tour again, and perhaps his successor in the parish could do it as well.  Amazingly, the manuscript survived the centuries and is kept in the library of Exeter Cathedral, with that sequential list on the back in Father Geoffrey's scrawling handwriting.

Five hundred years later, a medievalist in Exeter, Professor Avril Henry, discovered that the handwritten notes on the back of this manuscript formed Father Geoffrey's carefully ordered list of the households of his parish, divided into fourteen groups.  Some of those groups were identified alongside days of the week.  Professor Henry interpreted the list as a tour of the parish.  But, to interpret it as instructions for hearing confessions went against other evidence from medieval church records.  So Professor Henry was suggesting something new.

A few years further on, I came across Professor Henry's paper, and read about the controversy it had caused.  Her paper included a map of the parish, and the route that corresponded to those fourteen days and forty-eight places.  And I thought "travelling salesperson".  Could I prove that this was a systematic tour?  Statistical analysis, and aspects of the travelling salesperson problem with constraints in a two-dimensional plane seemed to say yes.  I drafted a paper based on my analysis.  Avril Henry and I discussed it.  She made some helpful comments about the historical context and my analysis.  I revised the draft and submitted it for publication.

Today, the resulting paper is available online.  I cannot prove that Father Geoffrey did what I have described.  The story above is speculation based on the handwritten notes, and an attempt to make sense of them using medieval history, operational research and statistics.  But the paper gives the evidence to support the story.  If you have access to the journal OR Insight, you can read it for yourself.  If not, here is the abstract.  (And I am allowed to send you a copy if you ask!)

For more information about this beautiful, and secluded part of Devon, go to the Tamar Valley AONB site.

So, let us raise a toast to the memory of Father Geoffrey of Bere Ferrers, pioneer of systematic route planning, and - perhaps - cost-benefit analysis!




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