the other half had neither glass nor ribbon over it; and although the heat was greater than on the preceding day, no magnetism was produced.
On the 2d of September, thermometer at noon 68°, a piece of neutral white steel acquired polarity from exposure to the sun, enveloped in green ribbon, one half being covered with paper as before.
On the 3d of September, thermometer at noon 68°, two pieces of neutral spring became magnetic, one exposed in a violet-coloured ribbon, and the other in blue glass, while a similar piece of spring was in no way affected by exposure to white light: the half of each was covered with paper.
September the 4th, thermometer at noon 68°, five large sewing needles, two inches long, were exposed to the sun's rays, one in blue glass, one in green glass, one in violet ribbon, one in green ribbon, and one in white light; the half of each was covered with paper. Of all these two only became magnetic, namely, those in the blue glass, and in the violet ribbon.
On the 20th of September, thermometer at 69°, I placed pieces of steel enveloped in violet and green ribbon, and under glass of various colours, in different positions with regard to the magnetic meridian and dip. 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
