Abstract
I VENTURE to draw attention to an error relating to the above subject, which, originating with Wertheim, still holds a place some of our modern books on science. According to Wertheirn, the velocity of sound in iron and steel is increased by rise of temperature not extending beyond 100° C. Now in no sense whatever is this statement correct. It is true that the longitudinal elasticity of iron, as determined by the static method. will be found greater at 100° C. than at 0° C., provided we begin with the lower temperature first and the wire has not, after the original annealing, been previously raised to 100° C.; but the apparent temporary increase of elasticity is really a permanent one (Phil. Trans., part i., 1883, pp. 129-131), and if the wire be repeatedly heated to 100° C. and afterwards cooled, subsequent tests will always show a less elasticity at the higher temperature than at the lower, if sufficient rest after cooling be allowed. When, however, we come to such small molecular displacements as are involved in the passage of sound through a wire, even the apparent increase of elasticity mentioned above vanishes. I have been able to prove that, when an iron or steel wire is thrown into longitudinal vibrations, so as to produce a musical note, the pitch of this note becomes lower as we raise the temperature, even when the wire is heated for the first time after it has left the maker's hands.
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TOMLINSON, H. The Effect of Change of Temperature on the Velocity of Sound in Iron. Nature 33, 582 (1886). https://doi.org/10.1038/033582b0
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DOI: https://doi.org/10.1038/033582b0
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