I've prepared a Thanksgiving Webpage with history of the holiday, excerpts from public proclamations of it, and links to those public proclamations. It is interesting to see how deeply religious the presidential proclamations have been, and that even Bill Clinton did not excise God from the holiday. Lincoln's is one of the most eloquent:

I do therefore invite my fellow-citizens in every part of the United States, and also those who are in foreign lands, to set apart and observe the last Thursday of November next as a day of thanksgiving and praise to our beneficent Father who dwelleth in the heavens. And I recommend to them that while offering up the ascriptions justly due to Him for such singular deliverances and blessings they do also, with humble penitence for our national perverseness and disobedience, commend to His tender care all those who have become widows, orphans, mourners, or sufferers in the lamentable civil strife in which we are unavoidably engaged, and fervently implore the imposition of the Almighty hand to heal the wounds of the nation and to restore it, as soon as may be consistent with the divine purpose, to the full enjoyment of peace, harmony, tranquillity, and union. (Lincoln, 1863)

To return to Eric Rasmusen's weblog, click http://php.indiana.edu/~erasmuse/w/0.rasmusen.htm.