SIR,--In August last I received a letter from Mr. Isaac McPherson of Baltimore, on the controversies subsisting between yourself and some persons in that quarter interested in mills. These related to your patent rights for the elevators, conveyors, and hopper-boys; and he requested any information I could give him on that subject. Having been formerly a member of the patent board, as long as it existed, and bestowed in the execution of that trust much consideration on the questions belonging to it, I thought it an act of justice, and indeed of duty, to communicate such facts and principles as had occurred to me on the subject. I therefore wrote the letter of August 13, which is the occasion of your favor to me of the 7th instant, just now received, but without the report of the case tried in the circuit court of Maryland, or your memorial to Congress, mentioned in the letter as accompanying it. You request an answer to your letter, which my respect and esteem for you would of themselves have dictated; but I am not certain that I distinguish the particular points to which you wish a specific answer. You agree in the letter, that the chain of buckets and Archimedes screw are old inventions; that every one had, and still has, a right to use them and the hopper-boy, if that also existed previously, in the forms and constructions known before your patent; and that, therefore, you have neither a grant nor claim, to the exclusive right of using elevators, conveyors, hopper-boys, or drills, but only of the improved elevator, the improved hopper-boy, &c. In this, then, we are entirely agreed, and your right to your own improvements in the construction of these machines is explicitly recognized in my letter. I think, however, that your letter claims something more, although it is not so explicitly defined as to convey to my mind the precise idea which you perhaps meant to express. Your letter says that your patent is for your improvement in the manufacture of flour by the application of certain principles, and of such machinery as will carry those principles into operation, whether of the improved elevator, improved hopper-boy, or (without being confined to them) of any machinery known and free to the public. I can conceive how a machine may improve the manufacture of flour; but not how a _principle_ abstracted from any machine can do it. It must then be the machine, and the principle of that machine, which is secured to you by your patent. Recurring now to the words of your definition, do they mean that, while all are free to use the old string of buckets, and Archimedes' screw for the purposes to which they had been formerly applied, you alone have the exclusive right to apply them to the manufacture of flour? that no one has a right to apply his old machines to all the purposes of which they are susceptible? that every one, for instance, who can apply the hoe, the spade, or the axe to any purpose to which they have not been before