One idea is to look at the two boat trips, carried out in the space of little over a year, both beginning at Salter's Boatyard underneath Folly Bridge, one going up river for a picnic next to the ruins of Godstow Abbey and the second coming downstream to Nuneham Courtney. The first marks the birth of the fictional Alice, the second, the end of Carroll's friendship with the real Alice. In between, it's clear that the two became too close, certainly for Alice's mother, Mrs Liddell's comfort. For all involved it was an extraordinary year.
The trip to Godstow on 4th July 1862 is well documented. Carroll had already known the Liddell sisters for several years, had taken their photographs many times but on this memorable summer's day the Carroll began to tell a story with Alice as the protagonist. She begged him to write it down. The day after on his way to London he sketched out some chapter headings.
It took him a while to put the story down and to illustrate it. Meanwhile he continued to spend time with children, taking them to see the fireworks in celebration of the Prince of Wales' wedding. He comforted them when their new baby sister died in May; but he also shared their excitement when the newly married Edward brought his bride to Christchurch three months later.
Then on 25th June 1863 comes the second trip - a more formal arrangement with the entire Dean's family and a couple of impressionable young aristocratic undergraduates, who were perhaps brought along to introduce, Alice's older sister, 14 year old Lorina, to the kind of men she should look to marry.
The party was too large to all fit into the coach arranged for their return to Oxford and so Carroll was asked to take the three sisters across the fields to Culham station to catch the train. This unchaperoned excursion was unusual and Carroll's diary entry makes it clear that he was delighted to be asked.
But then it goes quiet. Two days later Carroll is, rather unusually, forcefully demanding the children come to be photographed - but it's clear that what ever occurred on the journey back to Oxford had prompted Mrs Liddell to call time on Carroll's friendship.
So what happened? There are several theories, but the one that seems most plausible is that in the abandon of the moment Carroll and Alice played out a courtship of sorts. Did he propose (as Alice's son suggested to a journalist in the 1930s)? Did she tell him she loved him? Or, less evident, was Lorina the focus of Carroll's attentions (as suggested by Jenny Woolf in her recent biography?) Either way the sisters own excited retelling of events once back at the Deanery persuaded Mrs Liddell that they should spend less time in Carroll's company.
From this moment on Carroll seems a diminished figure. He completed the story for Alice and gave it to her as a present 'in memory of a summer's day' in November 1864, but when, a year later, John Tenniel asked him for an image of Alice to base his illustrations for the published version on, Carroll didn't send him any of the Liddell photos, but rather those of a new friend Mary Hilton Badcock (see image), whose large forehead and blond hair set her as the model for the immortalised image of the Alice of the books and movies.