by those of Barlocci and Zantedeschi. The former found that a natural magnet which was capable of supporting a pound weight, had its power almost doubled by exposure to strong sunlight for four-and-twenty hours. Zantedeschi exposed a magnet which would carry fifteen ounces to the sun for three days, and increased its power two and a half times. These experiments seem almost to decide the fact of the power of white and violet light to induce magnetic force; but a series of researches by a philosopher who without doubt is greater than any of those already mentioned, seems to throw some doubt on the facts we have related above.
Before concluding, we must add a few more facts relating to the existence of invisible rays at both ends of the spectrum. "The visible portion of the spectrum," says Dr. Tyndall, in one of his Royal Institution lectures, "simply marks an interval of radiant action, the rays existing in which bear such a relation to our visual organs, as to be capable of exciting in them the sensation of light. Beyond this interval, in both directions, right and left, the radiant action continues to exercise itself, but the rays emitted are dark, in consequence of their exerting no influence on our eye. Those that exist beyond the red ray are capable of producing heat, while those that are beyond the violet excite chemical action. These invisible violet rays can be actually made perceptible to the eye, or, in other words, the undulations or waves proceeding from this end of the spectrum can be made to strike against certain substances and induce luminous vibrations, so as to connect the dark space beyond the violet with a brilliantly illuminated band. I have here a substance capable of effecting this change. The lower half of this sheet of paper has been moistened with a solution of sulphate of quinine, the other half being left in its ordinary condition. I will now hold the paper in such a manner that the line that separates the prepared half from the
