of the more refrangible solar rays, 135 



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 spec- 

 trum ; 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 tv*^o 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 hap- 

 pened 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 expo- 

 sure to the rays in order to acquire polarity. Large bodkins 

 were exposed to the violet rays without effect, the mass per- 

 haps 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 



