of luxury mechanical watches. But Fatio's efforts as an inventor extended into many areas beyond watchmaking. To optimise the capture of solar energy and thereby increase agricultural yields, Fatio suggested building sloping fruit walls, precisely angled to maximize the collection of heat from sunlight. Having supervised the building of such walls in Belvoir Castle, in 1699 he published an illustrated treatise that described his invention and included theoretical considerations about solar radiation. That work appeared with the imprimatur of the Royal Society. Fatio also proposed a tracking mechanism that could pivot to follow the Sun. Such ideas were superseded by the development of modern greenhouses. One must add to the catalogue of Fatio's inventions his early work on improving the grinding of lenses for the objectives of telescopes, as well as his later proposals for taking advantage of a ship's motion to grind corn, saw, raise anchors, and hoist rigging. He also contrived a ship's observatory and measured the height of the mountains surrounding Geneva, planning, but never completing, a detailed map of Lac Léman. Push-shadow gravity Fatio considered that his greatest work was his explanation of Newtonian gravity in terms of collisions between ordinary matter and aetherial corpuscles moving rapidly in all directions. Fatio was motivated by Huygens's earlier work on a "mechanical" explanation of gravity in terms of contact interactions between ordinary matter and an aether, and perhaps also by the success of his explanation of zodiacal light as sunlight scattered by an interplanetary cloud of fine particles. The need to make the collisions between ordinary matter and the aetherial corpuscles inelastic implied that Fatio's aetherial corpuscles must also exert a drag resistance on the motion of celestial bodies. Fatio therefore failed to interest Huygens (who believed in the conservation of vis viva) in his proposal. Huygens may also have found Fatio's theory uncongenial because it assumed an empty space in which the aetherial corpuscles moved, a view contrary to the plenism of Huygens and Leibniz, who conceived of the aether as a fluid pervading all of space. Finding that the drag resistance was proportional to the product of the speed and the density of the aetherial corpuscles, while the gravitational attraction was proportional to the density and the square of the speed of the corpuscles, Fatio concluded that the drag could be made negligible by decreasing the density while increasing the speed. However, despite some initial enthusiasm