This is the second of two Spenserian sonnets Henry Francis Cary sent to Anna Seward, this in a letter of 1 June 1789; it was first printed in 1847.
Cary to Seward: "I cannot help thinking that a distinction should be made between the Miltonic and Spenserian sonnet; the first may be used on grave or sublime, the latter on tender subjects; the diction of the former ought to be elevated yet simple, and should require a sort of majesty by the pauses and breaks peculiar to blank verse; that of the latter should be neat, pointed, and smooth throughout. Two of Milton's sonnet (viz., that to Cromwell, and that which begins 'Captain or Colonel,') and yours on Ingratitude, form examples of perfection in one species of this writing, some of Hayley's and Mrs. Smith's in the other.... Need I say that I denominate this species of sonnet the Spenseric, because Spenser's sonnets are of this construction?" 1 June 1789; 1:34-35.
George Sanderlin, "A Bibliography of English Sonnets 1800-1850" (1941) notes two other Spenserian sonnets by Cary after 1800, not located.
Sweet are the tuneful murmurs of the spring,
Gurgling from yon high oak's incumbent base,
Whose roots around the mossy fragments cling;
Whose dark brown branches wave with savage grace;
Sweet o'er their pebbly bed with silent pace
Through the green sloping banks the waters glide,
While the pale moon beholds her beauteous face
In the clear mirror of the glassy tide:
To that calm breast where peace and joy reside,
What heavenly raptures might these scenes impart!
And yet to his, where brooding sorrows hide
Their serpent stings, and point the venom'd dart,
They add, alas! nor pleasure nor relief,
But cast in deeper shades the gloom of grief.