We cannot tell what influence finally launched this high-piled avalanche of thrice-sifted snow.

The time is better ascertained.

Aubrey refers it to 1658, the last year of Oliver's Protectorate.

As Cromwell's death virtually closed Milton's official labours, a Genie, overshadowing land and sea, arose from the shattered vase of the Latin Secretaryship.
Nothing is more interesting than to observe the first gropings of genius in pursuit of its aim.

Ample insight, as regards Milton, is afforded by the precious manuscripts given to Trinity College, Cambridge, by Sir Henry Newton Puckering (we know not how he got them), and preserved by the pious care of Charles Mason and Sir Thomas Clarke.