I recd. in due time your letter of May 10th inclosing a continuation of your observations on the "Natural boundaries of Empires". The views you have taken of the subject, give it certainly an attractive interest. But I must retain the impression, that they may reasonably be qualified by the progress of human Art in controuling the operation of physical causes.

I should have sooner acknowledged your favor but for an indisposition which proved tedious, & from which I am not yet entirely recovered. With cordial respects & good wishes.