SIR,--Your favors of June 16th, July 15th, 18th and 31st, I have the honor now to acknowledge. I have been for a month past so closely employed, that it has been out of my power to do myself the pleasure sooner of writing to you on the several subjects they contain. I formerly wrote you the reason why Mr. Grand has not paid your bills; that is to say, the want of a letter of advice. As to the notary's calling on me as inserted in the protest, I do not remember that he did. Persons calling on me with demands on account of the United States, I generally refer to Mr. Grand, with information that I have nothing to do with the moneys of the United States. Mr. Grand, by refusing to make payments without my order in many cases, has obliged me to interfere till I could obtain instructions to him from the treasury as to the manner in which he should govern himself. With respect to your bill, I am thoroughly satisfied he had no reason for not paying it but the want of a letter of advice. Had there been one, I would have ordered the payment; but this being a caution required between private individuals, it was less to be dispensed with in the case of the public. I believe I may venture to assure you, that if you will always write a letter of advice with your bills, they will always be honored. If the mode of doing business at Madrid would admit their being drawn at so many days' sight, it would be better, because it would allow time to consult you, if the letter of advice is miscarried. * * * * *