I've just finished a post over on the MHS blog with some interesting (to me, anyway) new findings about William Jenks' wonderful 1808 pamphlet Memoir of the Northern Kingdom, which postulates the breakup of the Union into three sections, &c. I started writing about it in the context of an offhand remark he makes in the essay which refers to the MHS ("that valuable library of domestick history, collected by the friends and associates of Belknap and Minot"), but since a large collection of Jenks' papers were handy I started poking around, and ended up finding a really neat letter from Jenks sending the essay to the publisher, then some diary entries describing his feelings about its debut in print, &c.
And then there was the tantalizing footnote I found which suggested that the manuscript of the essay is somewhere among the Jenks papers ... if it is, I can't find it anywhere. Nonetheless, I was surprised to find what I did, and I hope others will enjoy it as well.