Note on Franklin’s Sketch of How to Force a Wheel Round by Gunpowder
AD: American Philosophical Society
For some years we have been trying and failing to answer two questions about this sketch: why and when was it made? The device as described would obviously never produce continuous rotation, if that was the intent; and a wheel that turned in spasms would have limited use. As for the date, no clue to it has appeared in the edited correspondence; one may of course be lurking in what is still unedited, but our present guess is that the drawing belongs to the years before the Revolution. Although Franklin’s experimental heyday was over by the time his British missions began, he was still following a wide variety of interests, from Polish windmills to the common cold, and might well have toyed with a new use for gunpowder. When he returned to America, and for years thereafter, leisure to indulge his curiosity was in short supply. That is our only ground for conjecturing that the sketch belongs to his English years or before.
To force a Wheel round with Gunpowder
ABC of Cast Iron, with an Inch squ. [?] Groove [in] the Sweep Face next the Wheel capable of receiving the Edge of the Wheel, which is likewise an Inch thick.
The Wheel not an exact Circle, but has a Shoulder at D, which comes down on the Charge of Powder confin’d in the Groove at E.
F a Piece of Wood, 1 Inch wide and 2 deep, to slide in a hole G thro’ the Piece ABC to come under and support the Charge of Powder, and to be push’d back by the Widening of the Wheel when it comes round.
By this Method, the Force of Gunpowder may possibly be apply’d to the raising of Weights, bending great Springs, and the like.