'Comparative magnitudes of the planets', c 1851.
© Science Museum / Science & Society Picture Library
One of a set of teaching cards published by James Reynolds & Sons, London, featuring a chart drawn and engraved by John Emslie. In two separate diagrams it shows both relative size of the planets and their distance from the Sun. Two small inset figures show how the appearance of Saturn changes as it goes around the Sun along with the phases of the planets Venus and Mercury. To put the scale of the Solar System in perspective, the chart lists the time taken by a cannon ball, fired at 1000 miles an hour from the Sun at to reach each planet.