other of the more refrangible rays had the same property as the violet. A set of needles carefully examined as before, were therefore subjected to the different rays of the solar spectrum; the needles exposed to blue and green rays, sometimes acquired the magnetic property, though less frequently, and requiring longer exposure than when the violet rays were used; but the magnetism seemed to be equally strong in these as in the examples of the violet rays. The part exposed became a north pole. The indigo rays succeeded almost as well as the violet.
Pieces of clock and watch spring were next tried, under the idea that they might, possibly from their blue colour, be more susceptible of magnetic influence, and it was the case; their greater extent of surface however, or their softness, may have contributed to this susceptibility. The pieces of spring were from two to three inches long, and from the eighth to the half of an inch broad. It was difficult to procure watch and clock spring free from magnetism; it even happened on one occasion, that although the roll of spring was neutral, the pieces into which it was cut became magnetic; in one instance the pieces were heated so as to deprive them of magnetism and colour; they then required longer exposure to the rays in order to acquire polarity. Large bodkins were exposed to the violet rays without effect, the mass perhaps being too great. When needles already magnetic were tried, their magnetism was increased. Dr. Wollaston was so kind as to lend me a very large lens, having its centre covered with paper, which he had used in his investigations respecting the chemical rays. The lens concentrated the violet rays, and produced a magnetic effect in a shorter time
