Like boys that run behind the loaded wain
For the mere joy of riding back again,
When summer from the meadow carts the hay
And school hours leave them half a day to play;
So I with leisure on three sides a sheet
Of foolscap dance with poesy's measured feet,
Just to ride post upon the wings of time
And kill a care, to friendship turned in rhyme.
The muse's gallop hurries me in sport
With much to read and little to divert,
And I, amused, with less of wit than will,
Run till I tire.--And so to cheat her still.
Like children running races who shall be
First in to touch the orchard wall or tree,
The last half way behind, by distance vext,
Turns short, determined to be first the next;
So now the muse has run me hard and long--
I'll leave at once her races and her song;
And, turning round, laugh at the letter's close
And beat her out by ending it in prose.

John Clare

http://www.poemhunter.com/poem/letter-in-verse/