1 72 Mrs. Somerville on magnetization by the Solar Rays. 



succeeded in producing magnetism under the circumstances 

 described ; I next tried the effect of exposing neutral pieces of 

 clock-spring to the sun, enveloped in violet and green silk. 

 The half of each was covered with paper as before, and the 

 pieces of spring then wrapped, one in green, and the other in 

 violet-coloured ribbon, were fixed to the inside of a pane of 

 glass in a window, where they were left exposed to the sun all 

 day ; in the evening both had become magnetic, although they 

 were two of the pieces of spring already said to have acquired 

 polarity more slowly, from having been heated ; and as before, 

 the parts exposed to the sun under the ribbon were north 

 poles. 



To learn if heat had any share in producing magnetism in 

 this case, I exposed three pieces of the same steel to a bright 

 sunshine, on the 1st of Septembei', the thermometer at noon 

 being at 70° : one half of each was covered with paper, but 

 the other half had neither glass nor ribbon over it ; and al- 

 though 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 3rd 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 si- 

 milar 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 un- 

 der 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 diminished force 

 of the sun; in consequence of which further experiments were 



deferred 



