From Oxford University’s current online exhibit of Kenneth Grahame’s Wind in the Willows and their famous Bodleian Library:
In the Spring of 1907, Kenneth Grahame and his wife travelled to Cornwall for a long holiday. Their seven year old son Alastair, or â€˜Mouseâ€™, agreed to remain with his nanny, Miss Stott â€“ but only if his father continued to tell him bedtime stories by post.
His father agreed and over the next few months sent Alastair fifteen letters recounting the reckless adventures of Mr Toad and the attempts of his long-suffering friends, Mole, Rat and Badger, to rescue him from his various scrapes and teach him how to behave properly. The descriptions of the river and surrounding landscape draw upon Grahameâ€™s own fond childhood memories of the countryside around the Thames.
The early letters to Alastair begin and end affectionately, combining real news with the story of Mr Toad. However, following Alastairâ€™s demand to be called â€˜Michael Robinsonâ€™ instead of his real name (which he decided he did not like), the letters abandon their chatty tone and simply tell the story, ending in each case, â€˜to be continuedâ€™.
The letters were carefully preserved by Miss Stott and given to Elspeth, who persuaded her husband that they would make a wonderful book. Grahame followed her advice, developing his narrative and publishing it in 1908 as The Wind in the Willows.
The original letters were given to the Bodleian Library by Elspeth Grahame in 1943, and can be read here.
Here is letter number 7 (click for a larger view):