135 
of the more refrangible solar rays. 
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 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 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 
