"These old Scottish airs are so nobly sentimental, that when one would compose to them, to 'south the tune,' as our Scotch phrase is, over and over, is the readiest way to catch the inspiration, and raise the bard into that glorious enghusiasm so strongly characteristic of our old Scotch poetry."
(Robert Burns's "Commonplace Book", quoted in The Complete Works of Robert Burns, Ed. Alexander Smith, Crowell, New York, 1887, p. 298.)
How many of Burns's songs would we NOT have if Burns's publishers (Thompson and Johnson) had had to clear the copyright for EVERY air ?
A report on the NINCH's (National Initiative for a Networked Cultural Heritage) January 11, 2000 Town Meeting on the Public Domain can be found here
Diane Zorich's talk on the public domain, presented at the meeting, is linked here. Here comments on the value of the public domain are here though in some ways I think Robbie Burns says it better.