Thanks for that. i am researching Lockyer’s work on sunspots when he projected the sun’s image on to a screen with a slit in it, over which he positioned a sunspot. With his spectroscope receiving the light of the spot, (I guess it was his 7 prism one) he noticed that the spectral lines were widened. This was years before Pieter Zeeman’s discovery of the splitting of spectral lines due to magnetism and Hale’s observations linking sunspots and magnetism.
David