I know no beast in England whose voice I do not account musical save and except always the braying of an ass.  The notes of all our birds and fowls please me without one exception.  I should not indeed think of keeping a goose in a cage, that I might hang him up in the parlour for the sake of his melody, but a goose upon a common, or in a farm-yard, is no bad performer.

Here he is no missfire rival of Horace or Milton or Prior, or any of the other poets.  Here he has arrived at the perfection for which he was born.  How much better he was fitted to be a letter-writer than a poet may be seen by anyone who compares his treatment of the same incidents in verse and in prose.  There is, for instance, that charming letter about the escaped goldfinch, which is not spoiled for us even though we may take Blake’s view of caged birds: 

I have two goldfinches, which in the summer occupy the greenhouse.  A few days since, being employed in cleaning out their cages, I placed that which I had in hand upon the table, while the other hung against the wall; the windows and the doors stood wide open.  I went to fill the fountain at the pump, and on my return was not a little surprised to find a goldfinch sitting on the top of the cage I had been cleaning, and singing to and kissing the goldfinch within.  I approached him, and he discovered no fear; still nearer, and he discovered none.  I advanced my hand towards him, and he took no notice of it.  I seized him, and supposed I had caught a new bird, but casting my eye upon the other cage perceived my mistake.  Its inhabitant, during my absence, had contrived to find an opening, where the wire had been a little bent, and made no other use of the escape it afforded him, than to salute his friend, and to converse with him more intimately than he had done before.  I returned him to his proper mansion, but in vain.  In less than a minute he had thrust his little person through the aperture again, and again perched upon his neighbour’s cage, kissing him, as at the first, and singing, as if transported with the fortunate adventure.  I could not but respect such friendship, as for the sake of its gratification had twice declined an opportunity to be free, and consenting to their union, resolved that for the future one cage should hold them both.  I am glad of such incidents; for at a pinch, and when I need entertainment, the versification of them serves to divert me....

Cowper’s “versification” of the incident is vapid compared to this.  The incident of the viper and the kittens again, which he “versified” in The Colubriad, is chronicled far more charmingly in the letters.  His quiet prose gave him a vehicle for that intimacy of the heart and fancy which was the deepest need of his nature.  He made a full confession of himself only to his friends.  In one of his letters he compares himself, as he rises in the morning to “an infernal frog out of Acheron, covered with the ooze and mud of melancholy.”  In his most ambitious verse he is a frog trying to blow himself out into a bull.  It is the frog in him, not the intended bull, that makes friends with us to-day.