It is the evening of 5 September 1784. As darkness descends on the village of Datchet, the bustling activity of the day slowly draws to a close. A few gentlemen, mostly in pairs, walk the streets at a leisurely pace, taking their evening constitutionals, quietly discussing the day’s events. Their way is lit by a few widely spaced lamps, but these will be extinguished shortly; no need to waste precious fuel lighting streets long after everyone has gone to bed. The doors of the village pub open and close with diminishing regularity as the last of the patrons leave and make their way home. By 9:30 p.m. the village is largely quiet, save for the occasional bark of a dog.

It is a beautiful, star-lit night with a slight breeze and the air is crisp, suggesting that the cool days of autumn are not far off. After several days of cloud the moonless skies are clear and the brilliant summer Milky Way arches overhead, seen in all its glory. A short way from the village centre stands a solid two-storey house with a low stone wall extending away down the road. The house is dark save for the light of a single lamp near an open window on the second floor. In the garden the silhouette of a curious structure can be seen rising into the night sky, a peculiar construction of slanted spars and cross-beams, integrated with a pair of ladders on both sides. It appears to be more than 20 feet high and in the centre is a considerable tube, like a cannon but far larger, pointed almost vertically into the sky. There is a small platform off to the side of the tube near the top and one can see that there is a man standing there, leaning over the tube in the darkness. He is silent for a while but then calls out quietly to the ground below and all of a sudden the structure moves ever so slightly, turning on the casters supporting it. There is another man, this one standing at the base of the structure, who next turns a hand crank slowly just above his head. He stops immediately upon a second command and the night is again silent for several minutes.