DEAR SIR,--I returned about three weeks ago from a very useless voyage; useless, I mean, as to the object which first suggested it, that of trying the effect of the mineral waters of Aix, in Provence, on my hand. I tried these, because recommended among six or eight others as equally beneficial, and because they would place me at the beginning of a tour to the seaports of Marseilles, Bordeaux, Nantes and L'Orient, which I had long meditated, in hopes that a knowledge of the places and persons concerned in our commerce, and the information to be got from them, might enable me sometimes to be useful. I had expected to satisfy myself, at Marseilles, of the causes of the difference of quality between the rice of Carolina, and that of Piedmont, which is brought in quantities to Marseilles. Not being able to do it, I made an excursion of three weeks into the rice country beyond the Alps, going through it from Vercelli to Pavia, about sixty miles. I found the difference to be, not in the management, as had been supposed both here and in Carolina, but in the species of rice; and I hope to enable them in Carolina, to begin the cultivation of the Piedmont rice, and carry it on, hand in hand, with their own, that they may supply both qualities; which is absolutely necessary at this market. I had before endeavored to lead the depôt of rice from Cowes to Honfleur, and hope to get it received there on such terms, as may draw that branch of commerce from England to this country. It is an object of two hundred and fifty thousand guineas a year. While passing through the towns of Turin, Milan and Genoa, I satisfied myself of the practicability of introducing our whale oil for their consumption, and suppose it would be equally so, in the other great cities of that country. I was sorry that I was not authorized to set the matter on foot. The merchants with whom I chose to ask conferences, met me freely, and communicated fully, knowing I was in a public character. I could, however, only prepare a disposition to meet our oil merchants. On the article of tobacco, I was more in possession of my ground; and put matters into a train for inducing their government to draw their tobaccos directly from the United States, and not, as heretofore, from Great Britain. I am now occupied with the new ministry here, to put the concluding hand to the new regulations for our commerce with this country, announced in the letter of Monsieur de Calonnes, which I sent you last fall. I am in hopes, in addition to those, to obtain a suppression of the duties on tar, pitch and turpentine, and an extension of the privileges of American _whale_ oil, to their _fish_ oils in general. I find that the quantity of cod-fish oil brought to L'Orient, is considerable. This being got off hand (which will be in a few days) the chicaneries and vexations of the Farmers on the article of tobacco, and their elusions of the order of Bernis, call for the next attention.