172 Mr. G. Gore on the Molecular Movements and Magnetic 



further results showing the existence of additional molecular 

 changes. 



I took a well-annealed and straight bar of wrought iron 32 

 inches ( = 81*3 centims.) long and ^ of an inch ( = 9'5 millims.) 

 in diameter, supported it in a horizontal position by two wooden 

 clips, placed one end of the bar in a coil of thin insulated copper 

 wire connected with a distant galvanometer, and the other end 

 within a coil of thick insulated copper wire for attachment to a 

 voltaic battery ; the battery consisted of ten large Smee's cells. 

 A row of five Bunsen's burners was placed beneath the middle 

 part of the bar for the purpose of heating it to redness ; and the 

 bar at that part was between notched plates of firebrick to in- 

 crease the heat. With the whole of the bar at 60° F. ( = 15°*5 C), 

 on connecting the thick coil with the battery a deflection of 14° or 

 16° was obtained of the needles of the galvanometer ; but with 

 the middle of the bar at a red heat a deflection of only 4° could be 

 obtained. In a similar experiment with a bar 2 feet ( = 61 cen- 

 tims.) long and J an inch ( = 12*7 millims.) thick, the same bat- 

 tery, and more suitable coils of wire, a deflection of 20° or 22° 

 was obtained with the middle of the bar red-hot, and a powerful 

 swing of 90° with the whole of the bar cold, the needles striking 

 strongly against the stops of the galvanometer. With the bar of 

 iron entirely absent, no perceptible electrodynamic induction took 

 place. Similar but much less powerful results were obtained on 

 substituting a permanent bar magnet for the battery and thick 

 wire coil. A red heat, therefore, in the middle part of a wrought- 

 iron bar largely diminishes, but does not entirely prevent the trans- 

 mission of magnetism along the bar. 



The number of molecular movements and magnetic changes 

 which occur in wrought iron by change of temperature at a mo- 

 derate red heat are quite remarkable, and were gradually revealed 

 by the following experiments: — An iron bar 32 inches ( = 81*3 

 centims.) long and | of an inch ( = 9*5 millims.) thick, in a hori- 

 zontal position and diagonal to the magnetic meridian, was sur- 

 rounded at one end by a coil of thin insulated copper wire con- 

 nected with a distant galvanometer. On gradually heating the 

 middle part only of the bar to redness, when the temperature 

 acquired a low red heat a slight sudden deflection of the needles 

 occurred ; and on gradually cooling the bar a similar slight and 

 sudden deflection in an opposite direction took place, apparently 

 at the same temperature. The directions of the induced current 

 during the heating agreed with what would be produced by a 

 decrease of magnetism, and during the cooling with an increase of 

 magnetism. With a bar 2 feet ( = 61 centims.) long and \ an 

 inch ( = 12'7 millims.) thick, and the north pole of a small per- 

 manent bar magnet lying in contact with one end of the bar, the 



