Page:Somerville On the Magnetizing Power of the More Refrangible Solar Rays.djvu/2

Rh, and run through a small piece of cork, into which a conical cap of glass is inserted; the whole traverses on the point of a needle fixed perpendicularly in a stand.

I had no information at this time of the manner in which Professor M had conducted his experiments; but it occurred to me that it was not likely that if the whole of the needle were equally exposed to the violet rays, the same influence should, at the same time, produce a south pole at one end of it, and a north pole at the other. I therefore covered half of the needle with paper, and fixed it to the panel with wax, between ten and eleven in the morning, in such a position that the uncovered part of it should be exposed to the violet rays. The needle was placed in a vertical plane, nearly perpendicular to the magnetic meridian, and inclined to the horizon. As I had not a heliostat, it was necessary to move the needle in a direction parallel to itself, to keep the exposed portion of it constantly in the violet ray.

The sun was bright at the time, and in less than two hours I had the gratification to find that the end of the needle which had been exposed to the violet rays attracted the south pole of the magnetic needle, and repelled the north pole. It had been previously ascertained that there was no iron near to disturb the results. The experiment was also repeated on the same day, under precisely similar circumstances, with the view of detecting any source of error that might have escaped observation in a first attempt; but the result was the same as in the first.

The season was so favourable that it afforded me daily opportunity of repeating the experiments, varying the size of the needles, always taking especial care to ascertain that