Earlier today I published a letter written by William Lindsay Gresham. In the comments, someone said that the contents of the letter belonged to Gresham's heirs rather than the owner of the letter. I thought that copyright material, such as that in a letter, created between 1923 and 1962 (as Gresham's letter was) was now in public domain. Just to be on the safe side, I took down the post. Anybody know for sure about the public domain status? Thanks.