Changes in Iron fyc. at different Temperatures. 173 



other end of the bar being enclosed within a coil 5 inches ( = 12*7 

 centims.) long, containing 20 layers or 2674 turns of " No. 27 " 

 (=0*25 millim. thick) insulated copper wire, connected with the 

 galvanometer, a slight deflection only of the needles was pro- 

 duced during the process of heating, and a quick motion of the 

 needles 3° in the opposite direction during the cooling. The 

 directions of movement agreed with the previous ones, and 

 showed that the bar suddenly increased in magnetic capacity 

 during cooling at a particular temperature of moderate red heat, 

 and apparently at the same temperature at which it undergoes 

 the anomalous diminution of cohesion and increase in length 

 already referred to. With the same bar and fine-wire coil, and 

 a coil 5 J inches ( = 13*3 centims.) long containing 8 layers or 

 464 turns of "No. 16" (=1*5 millim. thick) insulated copper 

 wire on the opposite end connected with the battery of ten large 

 Smee's elements, on gradually applying the heat the following- 

 effects took place : — When the bar became red-hot in the middle, 

 a small and irregular deflection of the needles of 1 J° occurred, 

 and the needles then returned steadily to zero, and no other de- 

 flection took place as the bar became somewhat hotter. The gas- 

 flames being now suddenly extinguished, in less than half a 

 minute the needles moved slowly 1° in the opposite direction, 

 then stopped, and then went rapidly 18J° further and quickly 

 back again, swinging nearly equally on each side of zero, and 

 soon settled near that point, and remained there during the whole 

 of the remainder of the cooling process. The directions of the 

 currents agreed with those previously obtained. 



In the next experiment an iron bar 2 feet ( = 61 centims.) long 

 and j of an inch ( = 19 millims.) thick was employed, with the 

 same battery, the thick- wire coil being 6 inches ( = 15*2 centims.) 

 long and containing 536 turns of "No. 17" (=1*5 millim. 

 thick) copper wire, and the other coil being 6 inches long and 

 containing 1960 turns of " No. 27" ( = 0*25 millim. thick) copper 

 wire. The order of procedure was the same as in the last experi- 

 ment. As soon as the bar had become red-hot, several minute 

 molecular changes and increases of magnetism in succession in the 

 bar took place as the bar became hotter, indicated by corresponding 

 small deflections of the needles. The bar being larger than the 

 previous one, it did not become quite so highly heated ; therefore 

 on stopping the gas the needles were instantly deflected 25° in the 

 opposite direction ; the current which produced this deflection 

 lasted in its full strength only a few seconds, and ceased entirely 

 in about one minute; it was succeeded, however, by another, 

 transient and feeble current in the same direction. By immer- 

 sing about 6 inches ( = 15*3 centims.) of the middle part of the 

 bar (which was at about 50° F. =10° C.) in a freezing-mixture 



