Invarn.

1902 Encycl. Brit. XXXIII. 805/2 For ordinary standards of length Guillaume's alloy (invar) of nickel (35·7 per cent.) and steel (64·3 per cent.) is used, as it is a metal that can be highly polished, and is capable of receiving fine graduations.

1921 Glasgow Herald 9 Nov. 11 Concentric brass and ‘invar’ tubes.

1928 J. E. Haswell Horol. iii. 29 The more recent discovery of the nickel-steel alloy, ‘Invar’, by Dr. C. E. Guillaume has, however, to a considerable extent revolutionised compensated pendulums.

1929 J. A. Ratcliffe Physical Princ. Wireless iii. 50 The oscillating system..is not an electrical circuit, but is a tuning-fork made of ‘invar’ metal, whose frequency remains very constant under all conditions.

1955 Sci. Amer. Sept. 165/1 The pendulum is still the standard for absolute values of gravity, but nowadays the instrument most commonly used is the gravimeter, a supersensitive version of the ordinary spring scale. The earth's pull is measured by the amount of stretching of a thin wire of silica or invar (a nickel-steel alloy) on which a small weight hangs.

1962 J. G. Tweeddale Metall. Princ. for Engineers iv. 106 Nickel may be used to reduce the coefficient of thermal expansion of steel, 36% reducing the coefficient practically to zero at room temperature when the carbon is 0·2% and manganese 0·5% (this alloy is sold in this country under trade names such as ‘Invar’ and ‘Nilo 36').

1971 R. J. P. Wilson Land Surveying viii. 134 Invar tapes are more delicate than steel tapes and cannot stand up to everyday survey use. Also the degree of accuracy they can provide is unnecessary on most survey work. However, they are invaluable on precise base measurements, all the British bases being measured with 100-ft invar tapes.