Astronomical chart by John Herschel Sketch of the positions of the Sun, Mercury, Venus, Jupiter and Saturn, relative to selected stars, including Castor and Pollux in the constellation of Gemini. The horizon line is marked in latitude 35 degrees north, half an hour after sunset as observed in India, on 1 July 1860. With a scale. The chart [referred to in HSF/2/1/36] was drawn to demonstrate the position of Mercury in June-July 1860, which had been mistaken for a comet by John Herschel. 13 November 1860