From Chapter 2:
Hentzner, the German traveller, who visited London in 1598, speaks of smoking being customary among the audience at plays, who were also supplied with "fruits, such as apples, pears and nuts, according to the season, carried about to be sold, as well as ale and wine." He was struck with the universal prevalence of the tobacco-habit. Not only at plays, but "everywhere else," he says, the "English are constantly smoking tobacco," and then he proceeds to describe how they did it: "They have pipes on purpose made of clay, into the further end of which they put the herb, so dry that it may be rubbed into powder; and putting fire to it, they draw the smoak into their mouths, which they puff out again through their nostrils, like funnels, along with it plenty of phlegm and defluxions from the head." This suggests that the unpleasant and quite unnecessary habit of spitting was common with these early smokers, a suggestion which is amply supported by other contemporary evidence.

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.