1894.] Dimensions of Wires and Rings of Annealed Iron. 233 



run the risk of spoiling so remarkable a specimen which it might turn 

 out to be difficult or impossible to replace. I therefore had another 

 ring made of iron from the same parcel, and believed to have been 

 cut from the same bar as the first. As, however, there was some 

 doubt about this latter point, I thought it better in the first instance 

 to anneal the new ring, and test it with a few turns of wire wound 

 upon it. Its behaviour was found not to differ materially from that 

 of Ring I. A very small elongation too small to be measurable : 

 was, however, observed with a magnetising force of only 3 C.G.S. 

 units, contraction beginning when the force was increased beyond this 

 value. The ring was then made red hot, and plunged into cold 

 water, with the object of hardening it, after which operation it was 

 replaced in its boxwood jacket and wound with 473 convolutions of 

 wire. 



This ring, called Ring II, was now found to give the same results 

 as the old unannealed rings and straight wires. As appears in 

 Table II and fig. 2, it attained its maximum elongation of about 

 33 ten-millionths in a field of 80, its original length was recovered in 

 a field of about 440, and a retraction of 11 ten-millionths occurred in 

 a field of 560. 



It appears, therefore, that as regards magnetic changes of dimen- 

 sions, an iron rod or ring is affected by annealing in very nearly the 

 same manner as by tensile stress,* a result which would hardly have 

 been anticipated.! 



Notes regarding Details. 



The apparatus and methods of experiment were the same as those 

 folly described in 'Phil. Trans.,' vol. 179, A, pp. 218224, the in- 

 strument being arranged so as to have a magnifying power of 43,745. 



The height of each little square in fig. 2 corresponds to a length of 

 about one-millionth of an inch (0*00000088 in. for Ring I and 

 0-00000103 in. for Ring II). 



The wires and rings were demagnetised by reversals before every 

 single observation. For a description and diagram of the demagnet- 

 ising apparatus, see loc. cit., p. 207. 



* ' Roy. Soc. Proc.,' vol. 47 (1890), p. 469. 



t The less so since the length of an iron rod seems to be diminished by anneal- 

 ing. A piece of iron wire 100 mm. long, cut from the same hank as that used in the 

 experiments, was heated in a Bunsen flame, and slowly cooled. It was found to 

 have contracted 0'07 mm., i.e., 0'07 per cent. It was then heated in the blowpipe 

 flame, and dropped into cold water. This produced an elongation of about 

 0'02 mm., leaving the wire - 05 mm. shorter than it was originally. These 

 measurements were made with a rough apparatus extemporised for the purpose, 

 and I do not attach much importance to the quantitative results, though there can 

 be little doubt that they are qualitatively correct. 



