Laudator Temporis Acti

Robert Gilfillan (1798-1850), "Blythe, Blythe, We'll A' Be Merry," in his Original Songs (Edinburgh: John Anderson, 1831), pp. 50-51:

Tune—"Andro and his cutty gun."

Blythe, blythe, we'll a' be merry,
    Let social harmony prevail;
Wha wad care for port or sherry,
    Whan they've Scotia's nappy ale?

It cheers the heart frae gloomy care,
    It gies new vigour to the mind:
It stilleth strife to rise nae mair,
    An' friendship's social link does bind.
                       Blythe, blythe, &c.

In days o' yore, how aft we've seen
    A bicker rouse a sang or tale;
Sae let us be as we hae been,
    For here's the nappy—here's the ale!
                       Blythe, blythe, &c.

Here's to the land o' rock and stream,
    The land o' mountain, muir, and dale;
The land where freedom's star does gleam,
    The land o' cakes and nappy ale!

Blythe, blythe, we'll a' be merry,
    Let social harmony prevail;
Wha wad care for port or sherry,
    Whan they've Scotia's nappy ale?

Blythe = blithe, probably an adjective (exhibiting gladness), although possibly an imperative of the obsolete intransitive verb blithe (rejoice, be merry).
Oxford English Dictionary, s.v. nappy, adj.¹, sense 1.a: "Of ale, beer, etc.: having a head, foaming; heady, strong..." Also a noun meaning beer, ale.
Oxford English Dictionary, s.v. bicker, n.¹: "'A bowl or dish for containing liquor, properly one made of wood.' Jamieson."