DEAR SIR,--I believe that when you left America the invention of the polygraph had not yet reached Boston. It is for copying with one pen while you write with the other, and without the least additional embarrassment or exertion to the writer. I think it the finest invention of the present age, and so much superior to the copying machine, that the latter will never be continued a day by any one who tries the polygraph. It was invented by a Mr. Hawkins, of Frankford, near Philadelphia, who is now in England, turning it to good account. Knowing that you are in the habit of writing much, I have flattered myself that I could add acceptably to your daily convenience by presenting you with one of these delightful machines. I have accordingly had one made, and to be certain of its perfection I have used it myself some weeks, and have the satisfaction to find it the best one I have ever tried; and in the course of two years' daily use of them, I have had opportunities of trying several. As a secretary, which copies for us what we write without the power of revealing it, I find it a most precious possession to a man in public business. I enclose directions for unpacking and using the machine when you receive it; but the machine itself must await a special and sure conveyance under the care of some person going to Paris. It is ready packed, and shall go by the first proper conveyance. As we heard two or three weeks ago of the safe arrival of the Hornet at L'Orient, we were anxiously waiting to learn from you the first impressions on her mission. If you can succeed in procuring us Florida, and a good western boundary, it will fill the American mind with joy. It will secure to our fellow citizens one of the most ardent wishes, a long peace with Spain and France. For be assured, the object of war with them and alliance with England, which, at the last session of Congress, drew off from the republican band about half a dozen of its members, is universally reprobated by our _native_ citizens from north to south. I have never seen the nation stand more firm to its principles, or rally so firmly to its constituted authorities, and in reprobation of the opposition to them. With England, I think we shall cut off the resource of impressing our seamen to fight her battles, and establish the inviolability of our flag in its commerce with her enemies. We shall thus become what we sincerely wish to be, honestly neutral, and truly useful to both belligerents. To the one, by keeping open market for the consumption of her manufactures, while they are excluded from all the other countries under the power of her enemy; to the other, by securing for her a safe carriage of all her productions, metropolitan or colonial, while her own means are restrained by her enemy, and may, therefore, be employed in other useful pursuits. We are certainly more useful friends to France and Spain as neutrals, than as allies. I hope they will be sensible of it,