Age of Reason, Footnote 6

As this book may fall into the hands of persons who do not know what an orrery is, it is for their information I add this note, as the name gives no idea of the uses of thing. The orrery has its name from the person who invented it. It is a machinery of clock-work, representing the universe in miniature, and in which the revolution of the earth round itself and round the sun, the revolution of the moon round the earth, the revolution of the planets round the sun, their relative distances from the sun, as the centre of the whole system, their relative distances from each other, and their different magnitudes, are represented as they really exist in what we call the heavens.

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