your letter of the 15th is recieved, but age has long since obliged me to withdraw my mind from speculations of the difficulty of those of your letter. that there are means of artifici[al]1 bouyancy by which man may be supported in the air, the baloon has proved, and that means of directing it may be discovered is against no law of nature, and is therefore possibl[e] as in the case of birds. but to do this by mechanical means alone in a medium so rare and unresisting as air2 must have the aid of some principle not yet generally known. however I can really give no opinion understandingly on the subject and with more good will than confidence wish you success.