Your favor of Feb. 28. was recieved on the 9th inst. and I should sooner have acknoleged it, but that writing has become difficult and irksome to me, and the occasions which call for it getting beyond my present powers of compliance. on the subject of your letter I must decline all opinion. it belongs to a deptmt of science with which I have long ceased to be familiar, and I do not now undertake any thing which requires a severe exercise of the mind. your own powers of combination invigorated by younger energies are much more to be trusted than the enfeebled investigations of an Octogenary , and what would be worth more than all the conclusions of theory, would be to make the machine and rely for certainty only on actual experiment. this is what I would recommend, and I return you your letter that your secret may remain in your own breast, and with my hope that you will accept my apology I assure you of my goodwill and respect

Th:J