Your drawings of a Polygraph I received in due time. It was my intention to have wrote, that you might have received the letter soon after your arrival at Monticella, as about that time I made the discovery, that the fault of incorrect writing with the Polygraphs ought not to have been attributed to the boards the paper rested on, but to the incorrectness of the drilling machine.

Having made a rough model of common boards, in order to see how much we might contract the size of the Desks with shorter Parellegrams; only of a length just sufficient to reach the extent of Post paper, when I put this machinery togather I was surprised to find it more incorrect than any I had done, although I had taken great pains in the workmanship, It puzled me for some days, and I was almost discouraged from going on with the Manufacture of Polygraphs. sometimes I was almost led to believe the principle, not good, yet my reason on it stiffled that opinion, and I then sought for the errors by a comparisson of the distances of the pivot holes, & thus discovered what had cost me infinite trouble,

My drilling machine was made thus: A and B drils fixed paralel in a frame, and mooved by the bow C. The form of the shoulders of the drils made in the form D, fitted exactly in holes in brass plates.

The frame holding the piece to be drilled confined between checks mooved forward to meet the drills, made of wood, and put togather with great care of well seasoned Stuff. All my acquaintance who had seen it admired the contrivance as excellent for correct drilling, Mr. Latrobe however once observed that Iron only could be depended on in Machines where great accuracy was wanted, and that he had often been deceived by wood. I am thus particular, to give you a full view of some of my difficulties in a work, which I presume we accord in opinion, of great importance, i.e. making with ease and expedition correct duplicates of writing. And, that you may now have assurance that it will be in my power to accomplish so desirable an object. Indeed nothing short of the great utility of the Polygraph could have induced me to have persevered so long, as I have done, even contrary to the wishes of many of my friends who appear to set a value on my labours. I flatter myself you will approve of my perseverance in this Instance, and I have a very good proof for that opinion, in veiwing your drawings now before me. The surface you have contrived promises better, than on the experience I have already had by a tryal of that mode, will justifie, which I shall explain after I have done with the drilling machine.

Determined to have correctness in this Tool, I had two frames made of strong bars of Iron, one to moove within the other, without the least lateral shake—they are ground togather with Emery. The movable frame brings the pieces to be drilled, as mentioned before, and in order that the drills may also be steady, they are made with conic shoulders, &c as the drawing explains.

A the conic shoulder which passes through hardened steel, B conic point followed by a Screw to keep the shoulder A close and steady. so that any wearing need not injure the truth of the Drill.

The brass plates in my first drilling Machine wearing, as they had square shoulders could not be brought up to fill them, and however small that motion might be, it was sufficient cause of error; for once a drill is a little out of the proper place, it will continue to drill in the same direction—which no doubt happened in the machinery made before, sometimes on one side, and at other times in a opposite direction, thereby making considerable difference of distance from one pivot hole to another in different parts of the parallel rulers.

I believe this explanation will satisfie you that the errors of incorrect writing, lay with the machinery and not with the boards under the paper. If a board is made of good wood, and the ends tenanted into clamps, and then screwed on a good bed, it will make a surface sufficiently true for our purpose. The weight of a great body of wood, slate or any other heavy substance, should be avoided, if no greater accuracy is obtained. If boards are put togather with the ends to form a flat surface, and the opposite ends enclosed in a box, the outermost ends exposed to moist air, will swell and the surface be then forced into a round form. And if slates, or even Iron unless very thick, or of great strength, be fixed in a frame that is liable to warp, it will make the slate or metal plate twist with it, therefore slate or marble will be useful only in Desks not considered portable and where the slate need have only a bed to rest on.

My cabinet-maker has begun your Polygraph, according to your Plan with the Cover to take off, but east and west it is a little longer than you drawing to give room to the machinery—and the upper hinge must also be a little different, to allow room for the perpendicular machinery to moove forward, and upward occasionally; to view what has been written. I wish also to give you a choice, therefore I shall as soon as possible have some that will fold up made of the smallest size; the Gallow 13 Inches high & of course the Box when folded up will be of the same width.

A Cover for the front made of small bars as you propose will require a circular top of at least 6 Ins. diameter, to obtain an easy motion, and the checks forming said grove must be thick to have sufficient strength and being on the outside of the Gallows will be more clumsey in appearance than your hinged cover.

Where the writing desk is not intended for traveling, then the surface from the top where the horizontal machinery is fixed to the bottom of the paper, it is best without a joint—however with substantial hinging, and square workmanship, it may be made sufficiently accurate for good writing.

I have some thoughts of contriving conic point hinges, as being more exact in the motion, and will be more out of the way than common hinges. however if the common kind is well screwed, there is very little danger of derangement from that quarter when the cabinet work is well squared and leveled. and I shall always endeavor to employ the best workmen.

In a machine to write with two Pens, I have one Pen with a screw to moove the Stay-pin & thus regulate the touch, and to those of three Pens, two of them have screws. The Pens have also undergone considerable improvements; the steel pens are better made; are firmly fixed in brass tubes, preferable to wood however hard, or even Ivory, which shrink considerably.

The Pen-bar has also undergone an important improvement. It has a steel rod to which the Pen-arms are screwed, this mooving within a small brass tube to the ends of it are arms soldered connecting the horizontal machinery, over this Tube is a semicircular tube with ends that also imbrace the steel rod, and, arms connecting the perpendicular machinery, the whole of this is much lighter then the brass bar to the Polygraph you have; is more correct & has less friction.

An important improvement which I have received from Mr. Hawkins; is a stay to govern the horizontal machinery, it is connected to the joint at A, and the other end B, is pined to the Desk.

This contrivance has enabled me to apply the suporting springs to a bar, instead of having the long spiral attached to the transverve parralells as formerly, it is now attached to an extra piece pinned to the nearest N. and S. parralell on the left hand, whence it has a sweeping motion of which the pin is the centre; this motion rendered smooth & easey by this extra piece terminating with a roller acting against another on the right hand north & south parralell, the extra piece thus running between the double bars of the parralell; by this means we avoid the inconvenience you mention of the strength of the spiral cord, both with respect to its force upwards and downwards; you will easily percieve that when you are writing at the bottom of the page the mechanical force is reduced, in consequence of the acting power having changed its situation. a. is the extra piece which is pinned at b. the center of its motion, a small long roller from a. to c. and another which it touches from d to e. reducing the friction; so that the spiral cord being fastened at a &c acts sometimes near the first and sometimes near to the second parralells.

Finding the brass frame holding the paper, have a tendency to make it rise in the middle, to remedy which, I now have only a single piece of strong brass to hold the paper at the top. A heavy ruller is a necessary appendage, to be used at pleasure. And instead of two colours of cloath, I now put two pieces of brass on the left hand to place the paper against, as being easier than placing the paper to a line.

I have been thus particular that you might have a comprehensive veiw of the alterations to be made in the Polygraph making for you, and, that if you approve or wish other improvements, that I may imbrace them as early as possible with the work on hand.

I am with the highest respect and reguard your friend