POWER OF THE SUN’S RAYS IN INCREASING THE STRENGTH OF MAGNETS.
Professor Barlocci found that an armed natural loadstone, which would carry 1½ Roman pounds, had its power nearly doubled by twenty-four hours’ exposure to the strong light of the sun. M. Zantedeschi found that an artificial horse-shoe loadstone, which carried 13½ oz., carried 3½ more by three days’ exposure, and at last arrived to 31 oz. by continuing it in the sun’s light. He found that while the strength increased in oxidated magnets, it diminished in those which were not oxidated, the diminution becoming insensible when the loadstone was highly polished. He now concentrated the solar rays upon the loadstone by means of a lens; and he found that, both in oxidated and polished magnets, they acquire strength when their north pole is exposed to the sun’s rays, and lose strength when the south pole is exposed.—Sir David Brewster.