Material
A number of materials have been used for balance springs. Early on, steel was used, but without any hardening or tempering process applied; as a result, these springs would gradually weaken and the watch would start losing time. Some watchmakers, for example John Arnold, used gold, which avoids the problem of corrosion, but retains the problem of gradual weakening. Hardened and tempered steel was first used by John Harrison and subsequently remained the material of choice until the 20th century.
In 1833, E. J. Dent (maker of the Great Clock of the Houses of Parliament) experimented with a glass Balance Spring. This was much less affected by heat than steel, reducing the Compensation required, and also didn't rust. Other trials with glass revealed that they were difficult and expensive to make, and there was a widespread opinion that they must be fragile. This latter objection is proved false by glass-fibre loft insulation and fibre-optic cables.
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