Page:The wonders of optics (1869).djvu/111

 direction. More than fifty years ago Dr. Morichini announced that the violet rays of the solar spectrum possessed the property of magnetizing steel needles that were previously free from magnetism. He produced this effect by concentrating the violet rays upon one-half of each needle with a convex lens, taking care to keep the other half concealed beneath a screen. After having continued this experiment for more than an hour, the needles were found to be quite magnetic.

Dr. Somerville tested Morichini's experiments by covering one-half of an unmagnetized needle an inch long with a piece of paper, and exposing the uncovered half to the violet rays of the spectrum, and found that the needle became magnetic in the course of a couple of hours, the exposed end being the north pole. The indigo rays produced almost the same effect, but the blue and green rays were much less powerful. When the needle was exposed to the yellow, orange, red, and invisible rays beyond the red, no magnetic effect was produced, although the experiment was continued for three days. Pieces of chronometer and watch springs were submitted to the same influences with a similar result; but when the violet rays were concentrated upon the needles and pieces of spring with a lens, the time necessary for magnetizing them was greatly reduced.

Baumgartner of Vienna and Christie of Woolwich also repeated these experiments. The latter philosopher found that when a needle of magnetized steel, copper, or even glass, vibrated by force of torsion in the rays of the sun, the arc of vibration diminished much more quickly than when the experiment was conducted in the shade. The sun's rays appeared to have the greatest effect upon the magnetized needle. From these results Christie concluded that the solar rays were capable of exerting a certain amount of magnetic influence.

These experiments were afterwards fully confirmed