266 Mr. G. Gore on the Magnetism of Electrodynamic Spirals. 



at moderate temperatures possessed both the magnetism due to 

 the current itself and that induced by the current upon the mole- 

 cules of the iron, whilst the copper possessed only that which 

 belonged to the current itself; and, fourthly, that by a rise of the 

 temperature of the iron to redness the induced portion of the 

 magnetism in it decreased, whilst the magnetism due to the cur- 

 rent alone remained equal to that in the copper. 



Experiment 4. — I now tried flat spirals of wire facing each 

 other about 4 centims. apart, with their axes in one horizontal 

 line (see fig. 3) ; the spirals were about 2*5 centims. in diameter, 



Ffc. 3. 



and each contained four turns of wire. With 20 centims. 

 length of iron wire *95 millim. in diameter, and 20 centims. of 

 copper wire 2*07 millims, in diameter, and the ten large Smee's 

 elements, the iron spiral became nearly red-hot ; at the first in- 

 stant of passage of the current the iron repelled the similar pole 

 of the needle somewhat more strongly than the cold copper ; but 

 as it became hot its excess of repulsion became less. I now sub- 

 stituted twelve Grove's cells (of the size already mentioned) as a 

 double series of five for the Smee's battery : the iron wire be- 

 came red-hot, whilst the copper one remained cold, and the needle 

 remained about equidistant between the two helixes. With a 

 flat helix of thin platinum wire substituted for the one of iron 

 the platinum one became nearly white-hot, and appeared to repel 

 the needle a little more than the copper ; it is difficult, however, 

 to make the spirals perfectly uniform, and to exactly determine 

 the middle point between them. 



Experiment 5. — In this experiment no needle was employed. 

 Two flat spirals (A and B, fig. 4), about 1/8 centim. in diameter, 



