From Thomas McLean
Frederick County May 2nd 1802.
Most Honored Citizen
Should any perticular mode or title of address to the first Magistrate of the United States exist; the unimportance of such form will sufficiently apologize for my ignorence of it.
Although a man in political eminence can always find matters of importance sufficient to exercise his utmost powers of judgment; yet, when any thing new in science, or in the application of principlis already known is presented; so far from being burdensome to a philosophic mind, that by changing for a moment the subtleties of political scrutiny for the simple truths of philosophy, the mind gains additional energy for its necessary pursuits. Whether the following is new or not I cannot at present determine: I can only say that my knowledge of it resulted from investigating the application of first principles. But before I proceed to the discription of what I judge to be new; let me first discribe an easy mode of comprehending the principles to be applied. If the Bridge-tree or that part of the frame of a merchant mill, on which the spindle is placed, was raised until the runner would not touch the bed stone, it would then require no more power to give it an hundred revolutions pr. minute than what would overcome the friction of the machinery at that speed. If this stone was taken off (which suppose to be four feet diameter) and another of equal weight, but of twenty feet diameter was put upon the same spindle; then because in both cases, there is no other resistance to the motion of the machinery than its friction; the same power which gives an hundred revolutions pr. Minute to one tun weight of four feet diameter, would give an equal number of revolutions to an equal weight of twenty feet diameter: their difference however, could be no more than what the resistance of the air might make, which must be very Small. And according to Forguson, centrifugal forces are as the square of their distance from the centre: and because the radius of a circle of four feet is two feet, and a circle of twenty feet is described by a radius of ten feet; therefore the centrifugal force would be, as the square of two to the square of ten, that is, as four to an hundred. If then, centrifugal force can be encreased, without a proportional encrease of the power necessary to produce it, that force can be applied; and this is what I judge to be new.—
Let A B be a cylinder of sheet copper or other metalic substance suppose two feet diameter and fifteen in length: let one end of this cylinder be fited perfectly tight with rivets and solder to the middle of the tube C D which should be of such size that the apertures covered with the valves F F (which must be fitted air tight) valves F F taken together shall be equal to the area of the cylinder A B. Let G be an hollow axle upon which is screwed the pump H. Let the Cylinder A B be set perfectly perpendicular upon its axis K, with its end B immersed in water. Let it be exhausted by the pump H until it stands full of water. In this condition it is plain that it would be as easy to communicate motion to it, as to the spindle of a merchant mill, and that it would require no more power to give it any degree of motion than what would overcome the friction of its centres and the resistance of the air to its motion at that speed. If the centrifugal tube C D is made fifteen feet in length, and to revolve upon its axles K G sixty times pr. minute, because the main radius of the centrifugal tube would then move with a velocity of thirty one feet pr. seccond; or in other words with the speed of water under fifteen feet head; therefore, the water contained in the tube C D propelled by centrifugal force to its extremities will press upon the inner surface of the valves with a force equal to fifteen feet head of water. If the velocity of this centrifugal mchine was encreased to seventy five and an half revolutions pr. minute, then the Centrifugal force of the water in the tube C D would open the valves F F and the water would issue with a speed of eight feet pr. seccond: because, the speed of the main radius of the centrifugal tube would then be eight feet pr. seccond more than the speed of water under fifteen feet head. If the velocity of the machine was still encreased, the pressure of the Atmosphere would supply it with water until the issue at the valves would require more than would be supplied by eighteen feet head, which is the remaining pressure of the Atmosphere after raising the water fifteen feet in the Cylinder A B. According to an [expe]riment which I made in order to ascertain the power necessary to overcome the friction [of a] merchant mill at a certain speed, it would seem that a centrifugal machine such as I have just discribed would raise thirty times as much water as would overcome the friction of the machinery at seventy five revolutions pr. minute. Thus it appears in theory, which is all I can give upon any subject; for my circumstance is such that it is not in my power to determine by experiment. I need not discribe to you its use if in practice it would correspond with this theory; but even then it can be of no use to me unless some person would give me something for my right of patent. If you can spare a moment from matters of more importance I would fondly know your sentiments of it. I live at the foot of the North mountain in Frederick County Virginia near the line of Berkeley. A letter to me directed to the care of William Sommerville post master Martinburg Berkeley County, Virginia would easily find its way to me. I have been thus minute, in discribing my place of residence because I am so little known
With the highest respect for your sentiments both moral and political I am
Your most obedient And very humble Servant
RC (DLC); torn at seal; endorsed by TJ as received 30 May and so recorded in SJL.
FORGUSON: McLean probably refers to James Ferguson, the self-educated Scots natural philosopher and inventor, whose writings on astronomy and mechanics sought to make their subjects comprehendable to lay readers. TJ owned copies of Ferguson’s works and recommended them to others (DNB description begins H. C. G. Matthew and Brian Harrison, eds., Oxford Dictionary of National Biography, In Association with The British Academy, From the Earliest Times to the Year 2000, Oxford, 2004, 60 vols. description ends ; Sowerby, description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, Washington, D.C., 1952–59, 5 vols. description ends Nos. 3735, 3793; RS description begins J. Jefferson Looney and others, eds., The Papers of Thomas Jefferson: Retirement Series, Princeton, 2004–, 6 vols. description ends , 1:581; Vol. 12:488; Vol. 16:543; Vol. 30:594; Vol. 32:180).