of the more refrangible Solar Rays. 169 



long, having previously ascertained that it was quite free from 

 magnetism, by repeated exposure of both ends of it to the 

 north and south pole of a very sensible magnetic needle, when 

 it was found equally to attract either pole in every instance. 

 The magnetic needle employed as a test in this experiment, is 

 made of a sewing-needle magnetized, 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 perpendi- 

 cularly in a stand. 



I had no information at this time of the manner in which 

 Professor Morichini had conducted his experiments; but it 

 occurred to me that it was not likely 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 perpendicu- 

 lar 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 op- 

 portunity of repeating the experiments, varying the size of the 

 needles, always taking especial care to ascertain that they 

 were free from magnetism. The needles were placed in various 

 directions in the plane of the magnetic meridian, sometimes in 

 the angle of the dip, sometimes perpendicular to the magnetic 

 meridian, and also at, various angles with regard to it. In 

 some cases the heads of the needles were exposed in place 

 of the points, to the violet rays. Perhaps it might have been 

 expected that the influence would have been greater in those 

 instances in which the needles were placed in the plane of the 

 magnetic meridian, and at the angle of the dip ; and, conse- 

 l <Juently, polarity might have been expected to take place in a 



Vol. 68. No. 341. Sept. 1826. Y shorter 



