the Points of Recalescence in Steel and Iron. 4-35 



caused the point I to be differently placed in the two experi- 

 ments. The wire in II carried the greater load. If the wires 

 are not loaded, the critical points are found to be at the same 

 height of ordinate. 



While I was working on the subject, it seemed probable 

 that the curious changes which took place in a wire when 

 heated and cooled might possibly be accompanied by some 

 sounds at the critical points. By means of a piece of 

 apparatus of simple construction 1 found this to be the case. 

 The apparatus was constructed thus : — A disk of mica 5 centim. 

 in diameter was fitted, like a telephone disk, into a circular 

 recess, turned out of a piece of wood. The disk was fixed at 

 right angles to a table. The steel wire under examination was 

 attached at one end to the centre of the disk, at the other to 

 a vertical post. The length of the wires tried varied between 

 5 centim. and 20 centim.; the diameters of the wires used 

 were about 0*5 millim. to 1*0 millim. The front of the recess 

 into which the mica disk was fitted was furnished with two 

 tubes, by means of which any sounds from the disk might be 

 conducted to the ears. 



After the tubes were fixed to the ears, a flame was applied 

 to the wire, usually the tip of a small Bunsen burner. On 

 heating the wire a certain temperature was reached at which 

 a sharp crackling sound was heard. As the temperature was 

 increased this ceased ; then, on removing the flame, at the 

 same temperature at which the first sound was heard, a second 

 similar sound occurred. This took place at the point of re- 

 calescence. As the wire cooled this ceased, and then, when 

 a temperature of about 490° C. was reached, a very sharp 

 sound was emitted. This third sound is, I believe, of interest, 

 as it appears to take place at the second critical point observed 

 by M. Osmond. During this sound experiment, the tempera- 

 ture was observed by means of the thermo-couple and gal- 

 vanometer. When the disk was furnished with a hollow cone, 

 as used in connexion with the phonograph, a person could 

 hear the effect at a distance of ten feet from the apparatus. 

 The first two sounds are of short duration, and might easily 

 be missed, if not carefully listened for ; but the third sound is 

 clear and definite. The wire used in these experiments was 

 steel pianoforte w T ire, annealed and straightened. I was 

 unable to get the effect when a wide flame was used, but with 

 a flame about 1 centim. wide the curious effect can be pro- 

 duced fifty times following from the same wire. The last 

 experiment was also arranged so that the steel wire when 

 heated should be in a strong magnetic field, produced by 

 a helix through the axis of which the steel wire passed, 



2 I 2 



