Abstract
R. E. GOULD has recently published a paper on the comparative performance of watches with the usual cut bimetallic balance wheels and steel hairsprings, and those of the new form having uncut monometallic balance wheels and elinvar hairsprings (Bureau of Standards J. Res., 12, April 1934). Elinvar is a nickel-steel alloy having a temperature coefficient of elasticity which is practically zero from 5 ° to 35 ° C. (41 ° to 95 ° F.). In the new watches the balance wheel is non-magnetic. The experiments show that the temperature-rate errors of the watches having the new vibrating assembly were smaller than the errors with ordinary watches. Instead of the usual parabolic curve of errors a curve approaching a straight line was obtained. The use of the new assembly ensures a very marked improvement in the performance of the watches. The new arrangement almost entirely overcomes the effects of magnetism, so that after a watch has been subjected to a strong magnetic field the rate is not affected. Very few watches maintain an absolutely uniform rate as the mainspring unwinds. If the number of seconds lost or gained since winding be plotted against time after winding, true ‘isochronism’ is represented by a straight line. So far as ‘isochronism’ goes, the new assembly does not give any material advantage over the old. Also various small changes, caused by altering the positions of the watches, are practically the same in both types.
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Elinvar Hairsprings in Watches. Nature 134, 318 (1934). https://doi.org/10.1038/134318a0
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DOI: https://doi.org/10.1038/134318a0