Edmond Halley as an old man, wearing a loose black robe over a brown coat. Beneath that, a white shirt with a fine squared collar at the neck. He wears a grey wig, shoulder-length and high up from the forehead. Behind him, in a curtained recess, are two bound books on a shelf. Another volume rests on a surface in front of Halley, over which lies, held in his right hand, a sheet of paper with a diagram of concentric circles.

The figure is from 'An account of the cause of the change of the variation of the magnetical needle with an hypothesis of the structure of the internal parts of the Earth…', in 'Philosophical Transactions of the Royal Society', vol.16, 1686–1692, pp.563–578, in which Halley attempts an explanation for the movements of the Earth’s magnetic poles through its internal structure.