Mary Godwin, born on August 30 1797, is 18 years old.
She and Percy are going to sail the Thames.
“I was then living at Marlow, and frequently walked over to pass a few days with him. At the end of August, 1815, we made an excursion on the Thames to Lechlade, in Gloucestershire, and as much higher as there was water to float our skiff. It was a dry season, and we did not get much beyond Inglesham Weir, which was not then, as now, an immovable structure, but the wreck of a movable weir, which had been subservient to the navigation, when the river had been, as it had long ceased to be, navigable to Cricklade. A solitary sluice was hanging by a chain, swinging in the wind, and creaking dismally. Our voyage terminated at a spot where the cattle stood entirely across the stream, with the water scarcely covering their hoofs. We started from, and returned to, Old Windsor, and our excursion occupied about ten days. This was, I think, the origin of Shelley’s taste for boating, which he retained to the end of his life. On our way up, at Oxford, he was so much out of order that he feared being obliged to return. He had been living chiefly on tea and bread and butter, drinking occasionally a sort of spurious lemonade, made of some powder in a box, which, as he was reading at the time the “Tale of a Tub,” he called the powder of pimperlimpimp. He consulted a doctor, who may have done him some good, but it was not apparent. I told him, “If he would allow me to prescribe for him, I would set him to rights.” He asked, “What would be your prescription?” I said, “Three mutton chops, well peppered.” He said, “Do you really think so?” I said, “I am sure of it.” He took the prescription; the success was obvious and immediate.
He lived in my way for the rest of our expedition, rowed vigorously, was cheerful, merry, overflowing with animal spirits, and had certainly one week of thorough enjoyment of life. We passed two nights in a comfortable inn at Lechlade, and his lines, “A Summer Evening on the Thames at Lechlado,” were written then and there. Mrs. Shelley (the second, who always bore his name), who was with us, made a diary of the little trip, which I suppose is lost.”
— Thomas Love Peacock writes about the sailing expedition to try and find the source of the Thames.