On the use of invar steel for precision balances

The Paper deals with certain advantages and disadvantages which accompany the use of invar steel for the beam of a precision balance. It was found that such a beam exhibits but little in the way of fatigue effects; and also that its sensitivity is nearly the same for all loads. Experiments prove that the resting-point of the balance notwithstanding the small coefficient of expansion of invar steel, may be appreciably affected by changes in temperature. This is attributed to slight relative movements amongst the several knife-edges and not to a differential lengthening of the beam itself. The instrument is affected by magnetic storms and also by the diurnal variations in the earth's magnetism. Magnetic effects may, however, be nullified by weighing according to the method of Gauss or by a method of difference. The conclusion reached is that provided due precautions are observed, invar steel is eminently suitable for the beams of high-grade precision balances.