From Chapter 4:
The variations in price of both Spanish and Virginia tobacco were largely due to the frequent changes in the amount of the duty thereon. In 1604 King James I, newly come to the throne, and full of iconoclastic fervour against the weed, raised the duty to 6s. 8d. per lb. in addition to the original duty of 2d. On March 29, 1615, there was a grant to a licensed importer "of the late imposition of 2s. per lb. on tobacco"—which shows that there must have been considerable fluctuation between 1604 and 1615—while in September 1621 the duty stood at 9d. Through James's reign much dissatisfaction was expressed about the importation of Spanish tobacco, and the outcome of this may probably be seen in the proclamations issued by the King in his last two years forbidding "the importation, buying, or selling tobacco which was not of the proper growth of the colonies of Virginia and the Somers Islands." These proclamations were several times confirmed by Charles I, the latest being on January 8, 1631; but they do not seem to have had much effect.

From Chapter 8:
The allusion in these verses to a "satiric wipe" refers to a passage in the poem entitled "Conversation," which Cowper had written in the previous year, 1781. In this passage tobacco is abused in terms which Cowper clearly felt to need modification after his personal intercourse with such a smoker as his friend Bull. In describing, in "Conversation," the manner in which a story is sometimes told, the poet says:

The pipe, with solemn interposing puff,
Makes half a sentence at a time enough;
The dozing sages drop the drowsy strain,
Then pause and puff—and speak, and pause again.
Such often, like the tube they so admire,
Important triflers! have more smoke than fire.