The London publisher Joseph Johnson (1738–1809) planned a new edition of Milton’s Paradise Lost, with illustrations by Henry Fuseli (1741–1825) and commentary by William Cowper (1731–1800), two of the most prominent artists and poets of the day. In 1792 Johnson gave Cowper this recently published edition of the poem, interleaved with blank pages on which he could make notes for the new edition. The two published volumes became four with the added blank pages: the Morgan has parts I–II (Vol. I, Books 1–6), while parts III–IV (Vol. II, Books 7–12) are at Princeton University Library (RHT 18th-106). Cowper’s wife Mary Unwin suffered from paralyzing strokes, and the deterioration of her health prevented Cowper from devoting his attention to Milton. He had only annotated the first two parts (Books 1–6) before Johnson thankfully cancelled the project in 1793. Cowper’s incomplete commentary was first published in 1808 (PML 129026).
For the critical edition of Cowper’s commentary, see The Letters and Prose Writings of William Cowper, vol. V: Prose 1756–c.1799 and Cumulative Index, edited by James King and Charles Ryskamp (Oxford: Clarendon Press, 1986), pp. 141–178.