Benjamin Franklin Papers

From Benjamin Franklin to Thomas Gilpin, 18 March 1770

To Thomas Gilpin

ALS: University of Virginia Library

London March 18. 1770


I receiv’d your Favour by the Hand of Mr. Abel James. An Accident happen’d to it in his Chest by the Breaking of a Bottle of some Liquid that obliterated part of it.5 I see however that it contains some good Remarks on the Advantages of Canals for internal Navigation in our Country, to which I heartily wish Success. What you tell me of the Practicability of navigating down Sasquehanah pl[eases] me extremely, as hitherto I had understood that to be impossible.

I wrote to you last Summer that I purpose to show your Machine to the Society of Arts.6 Since their Meeting I have till now been otherwise too busy to attend to such Things: but I lately pack’d it in its Box and sent it to their Store and am next Week to meet a Commitee of theirs to explain it to them. Many ingenious Men [have] seen it at my House and were much pleas’d with it. What they chiefly admire is not the Construction of the Sails but the Application of a single Crank to three separate Pumps.

I suppose you may not have had an Opportunity of knowing that the Manner of fixing your Sails, tho truly invented by you, has before been thought of by others. I did myself about 25 years ago make a little Model for W. Masters who had thoughts of executing it in large for Use.7 It was in all respects the same, except the Cord and Spring to each Sail which are in yours, and which I think may be a great Improvement; and except that I plac’d my Sails upright on their Ends; which I mention now for your Consideration whether the Force or Purchase is not thereby greater, no Part of it being so near the Center of Motion as when they lie on their Sides, and fall inwards; but of this I would not be positive. In a second Model I plac’d six Sails instead of four, for which there is good room when so plac’d upright, and I thought the Motion might thereby be more equable. A Friend of mine in Maryland, Mr. H Jones, to whom I had communicated this horizontal Windmill wrote a Paper about it which he printed, and with some Alterations erected a large one on his Land intending to apply it to the grinding of Corn; he nam’d it the Elephant from its suppos’d Strength: and when used in a Current of Water, which he also propos’d, would then have it call’d the Whale; but before his Elephant was finish’d a great Storm shatter’d it to Pieces, and he never repair’d it.8 My Son has now a Dr[aft?] of those Sails of mine done by Lewis Evans, in an 8vo manuscript Volume of Inventions collected by him.9 There is both a Plan of the Arms and Sails in their several Positions, and an upright View of them as applied to a travelling Carriage, which he fancied might be moved by them. My Son will readily shew it to you if you desire to see it.

Horizontal Windmills are not any where in general Use, except, as I have heard, in Poland. The Form there, is this. The Sails are all fix’d (in such a Position with regard to the Axis as the Radii of a Circle are to its Center) and upright Boards are fix’d all round them so as to throw the Wind to most Advantage against the Sails, let it come which way it will.

A the Axis. a, b, c, d, e, f, g, h, the Sails fix’d to the Arms. 1, 2, 3, 4, 5, 6, 7, 8, the standing Boards to throw the Wind against the Sails.

I have seen but two horizontal Windmills in all my Travels. The first was at Rhodeisland, where the Sails were in the Form of the Foresail and Mainsail of a Sloop, four little Masts with such Sails were fix’d upright on the four Ends of a horizontal Cross; the Sails fill’d and jib’d successively as the Cross went round: It was over a Turner’s Work Shop and the Application was to drive a large Lathe for turning heavy Mortars of Lignum Vitae. The other is now here at Knightsbridge near London, on the Top of a House for manufacturing painted Oil Cloths, and is used for grinding the Colours. The horizontal Wheel is in an octagon Tower with a Roof, but open all round the Sides; the Vanes are fix’d as in the Polish Mill; but to make it go, there are moveable Shutters, sufficient when properly plac’d to prevent the Wind acting on the coming Side of the Sails, and by leaving half the Tower open suffer it to act on the going side. This needs Attention and Care to shift the Shutters as the Wind changes and therefore seems not so good as the Polish Mill; nor is either of them so good as yours.

The Advantages of a Horizontal Windmill seem to me to be that the Building need not be so high as for the vertical one, therefore not so strong, therefore not so expensive; and it is always ready to receive the Wind from any Quarter, without the Trouble and Machinery necessary to bring the others about to face the Wind. But probably the others have the Advantage in some other respects which has continued them in general Use: their Force perhaps is greater.

I shall be glad to see your Contrivances for stopping or regulating its Motion. I dare say they are very ingenious. I once saw a very simple and as I thought it a very clever Method of regulating a Motion where the Power was applied unequally. It was this. From the Top of the upright Axis is hung two moveable Arms, with a Weight at the End of each. When the Axis began to turn, the Weights naturally receded farther from the Center rising higher at the same time; the greater the Force applied, the larger Circle they describ’d; and as the Force abated they sunk and describ’d smaller Circles in Proportion. By this Means the Excess of the Force applied was spent in raising the Balls and occasioning them to describe a greater Circle, whereby they pass’d thro’ more Space in the same Time, instead of its occasioning more Revolutions of the Axis in the same Time: thus those Revolutions continued to be equable. And this applied to your Windmill, by lengthening the Axis upwards to give room for hanging the Weights might I imagine occasion an equality of Motion always regulating itself, tho’ the Wind should be squally and unequal.

It must give you Pleasure to see the Contrivance of horizontal Wind mills become generally useful, and therefore you will excuse my mentioning a Manner of constructing them that almost every Farmer may execute without the help of any Workman, and which, or something like it, I have had an imperfect Account of as used in China.

Pumps in your ingenious Manner, tho’ very proper for Mines, &c. when skilful Persons could readily be had to repair them, might neither suit the Purse nor be so easily kept in order by the common Countryman, and so the Use of them would not generally obtain for the Purpose of Watering Lands. Suppose then that in an open Field by the Side of a Brook or Pond, one of those Windmills is to be fix’d in the cheapest and easiest Manner to raise Water: A short Stake drove into the Ground might receive the lower Point of the Axis, its upper End might be supported by Cords made of Leatherwood Bark carried out on all Sides and fasten’d to Pins drove into the Earth: If the Arms are to be six it might be cut three square above and below where the Arms are applied to it, which might be of Saplins, the Buts a little flatted next to the Axis, and bound on; their small Ends being out every way to make the Circumference of the Circle. The Sails might be of Reed or Rush Mats extended on slight Frames and hung above and below by bits of Rope or Cord. An open Trough of plain Boards laid slanting up from the Water, and a Number of little square Boards nearly fitting that Trough, fix’d at proper Distances to a small Rope in the Manner of a Chain Pump, and kept going by the Motion of the Axis, might bring the Water continually from the lower End of the Trough to the upper, and there discharge it into the Channel made to carry it away. If one Set of these Vanes does not raise it high enough, as they are cheap and easily made a second or third, or any Number might be used in different Parts of the Field one taking the Water from the Level where the other leaves it. Any Man with Hands might mend such a Machine when out of order. And in the Season of the Year when they would not be wanted to Work, they might easily be taken to pieces, and the Parts carried in under Shelter to preserve them from the Weather. This Idea I submit to your Consideration, and am with much Esteem, Your most humble Servant

B Franklin

A very bad Drawing, but may help a little to explain my meaning.1

[Note numbering follows the Franklin Papers source.]

5For Abel James, the bearer of the letter, and his business trip to London see BF to Evans above, March 17; for Gilpin’s letter see XVI, 216–18, where the extracts reprinted are presumably from a copy that Gilpin made for himself.

6See above, XVI, 175, where BF acknowledged receipt of a model of Gilpin’s pump. The only extant description of this model, and an inadequate one, is in APS Trans., I (1771), 339.

7Presumably the small windmill that BF designed to assist his electrical experiments, for which see above, III, 130. Masters was almost certainly William Masters, an experimental farmer and BF’s associate in civic enterprises in Philadelphia; see above, IV, 193 n, 214; VI, 312 n.

8BF’s friend was in all likelihood the Rev. Hugh Jones, an erstwhile professor of natural philosophy at William and Mary, who at the time of his death in 1760 had a parish and a farm in Maryland. See above, III, 324 n; Richard L. Morton, ed., The Present State of Virginia … by Hugh Jones … (Chapel Hill, [1956]), pp. 42–3. We have found no pamphlet by Jones on windmills.

9For Lewis Evans, surveyor, draftsman, and cartographer, see above, III, 48 n. He drew “all sorts of maps, plans, seacharts, prospects, and machines”: Pa. Gaz., Jan. 2, 1749/50.

1More than a drawing is needed to explain what BF means, for his skill as an artist did not match his mechanical skill. The vanes appear to be hung on cords that act as pivots, but three of the cords are in the center of the vanes and three are eccentric. In fact they would all have to be eccentric, so that as the arm moved into the windward side of its revolution the vane would rotate to point into the wind. BF also omitted the “spring” that he spoke of in Gilpin’s model; this was presumably a second cord, or sime similar stop, that held the vane rigid on the arm when before the wind. Without these details, which may be implied but are certainly not mentioned, the salient characteristic of the windmill would be that it did not work.

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