to Steel by the Sun's White Light. 20S 



and Mrs Somerville. It has conducted me to this result, that if 

 a piece of steel, of the size of an ordinary sewing-needle, of 

 which one or more parts are polished, and the others without 

 lustre, is exposed to the influence of the direct white light of 

 the sun, it takes a north pole at each polished part, and a south 

 pole at each unpolished part. The following is the process 

 employed. 



I took a wire of English steel, of the size of an ordinary 

 sewing-needle, and I heated it, so as to cover it entirely with 

 a black oxide. I then removed the oxide from one or more 

 places, by means of a hone, and I completed the polish with 

 chalk and a piece of lime tree, so as to form brilliant zones, 

 about two or three lines long. The steel thus prepared being 

 laid in a place perfectly exposed to the sun, was found at 

 the end of some time strongly magnetic, and in the manner 

 already mentioned. The time, every thing else being equal, 

 appeared to depend on the intensity of the solar light, for 

 when I concentrated the rays of the sun upon the polished 

 zones by means of a lens, I produced in a few minutes a mag- 

 netism, which would have required several hours with the 

 natural intensity of the solar rays. 



A piece of steel polished only at one of its extremities ac- 

 quires a north pole at that extremity, and a south pole at the 

 other. If the polished part occupies the middle, the two 

 extremities acquire a south pole, and the middle a north pole. 

 If the wire, on the contrary, is polished at its two extremities, 

 these acquire a north pole, and the middle a south pole ■ In 

 short, if the wire has several polished zones, each of them takes 

 north polar magnetism :, and the obscured zones south polar 

 magnetism. We may in this way develope any number of 

 magnetic poles, provided that the steel wire has a length pro- 

 portional to the number of poles required. 



I have thus been able to obtain easily eight poles upon a 

 wire eight inches long, but certainly of unequal intensity. I 

 have constantly found that the extreme poles were stronger 

 than the others, and that they preserve their magnetism longer. 



I have not been able to succeed in magnetizing, by the same 

 means, steel needles entirely covered with oxide, or perfectly 

 polished, nor other needles which had polished lines in the direc- 



