Mary Fairfax Somerville

“ The effect was produced with equal facility by throwing the spectrum on the floor of the room; but success could not always be depended upon even when the weather seemed most favourable.
I now made the following experiments with blue glass. Three needles free from magnetism, having one half covered with paper, were laid horizontally on the stone outside of a south window, under a dark blue glass coloured by cobalt, in a very hot sun; after remaining in this position between three and four hours, they were found to have become feebly magnetic, the uncovered part being a north pole. ”

“ Several acquired polarity, the uncovered part being the north pole. A piece of steel became more strongly magnetic than usual, exposed in green ribbon, the position of which had been perpendicular to the horizon, and nearly in the magnetic meridian. For some time I still obtained similar results, though the magnetism became more feeble as the season advanced, from the diminished force of the sun, in consequence of which further experiments were deferred till the return of summer shall afford me an opportunity of continuing them. ”

“ A set of needles carefully examined as before, were therefore subjected to the different rays of the solar spectrum; the needles exposed to blue and green rays, sometimes acquired the magnetic property, though less frequently, and requiring longer exposure than when the violet rays were used; but the magnetism seemed to be equally strong in these as in the examples of the violet rays. The part exposed became a north pole. ”