Mr. G. Gore on the Magnetism of Electrodynamic Spirals. 265 



Experiment 2. — In this experiment the spirals were 1*5 cen- 

 tim. in diameter and 2*9 centims. long, 

 and were placed parallel to each other, 

 as in fig. 2, and were formed of platinum 

 wire *82 millim. thick, and copper wire 

 2*05 millims. thick ; but in other re- 

 spects the arrangements were similar to 

 those of No. 1 experiment. With the 

 ten Grove's cells as one series the pla- 

 tinum wire was quite red-hot through- 

 out, and the copper wire cold, and the 

 pole of the needle remained equally re- 

 pelled by each spiral as before; and 

 with the cells as a double series of five, 

 the platinum wire was bright red-hot, 

 and the needle remained in the centre 

 the same as if no current was passing. 

 A bright red heat, therefore, did not 

 sensibly increase or decrease the mag- 

 netizing influence of the platinum spiral; 



and the magnetism of that spiral was independent of change of 

 temperature, and of the molecular state produced by change of 

 temperature. 



Experiment 3. — The arrangements were the same as in the 

 last experiment, except that an iron wire was substituted for the 

 platinum one, and ten large Smee's cells, 12 inches x 8 inches, 

 substituted for the Grove's battery. With an iron wire 1*42 

 millim. thick the iron wire became heated to about 200° C, and 

 repelled the needle much more powerfully than did the cold 

 copper spiral. With an iron wire *95 millim. thick the iron 

 spiral, though much hotter, still repelled the needle more strongly 

 than the copper one ; and also repelled it strongly after the cur- 

 rent was stopped and both the wires were quite cold, evidently 

 because it retained much of its induced magnetism. With a 

 " No. 23 " iron wire, *68 millim. thick, the iron spiral became 

 red-hot, and repelled the pole of the needle with but little greater 

 force than that of the copper spiral ; on shifting the copper spiral 

 to a distant part of the circuit and renewing the current, the iron 

 spiral repelled the needle strongly. This experiment shows : — 

 first, that an electric current of a given strength passing simulta- 

 neously through two similar spirals of wire, one of iron and one 

 of copper, produces at moderate temperatures a greater degree 

 of magnetism in the former than in the latter; secondly, that 

 when the iron wire attains a red heat its total magnetic power is 

 not much greater than that of the copper ; thirdly, that the iron 



Phil. Mag. S. 4. Vol. 40. No. 267. Oct. 1870. T 



