BRIDGMAN. — A SECONDARY MERCURY RESISTANCE GAUGE. 235 



any possible effect of the size of the capillary on its elastic behavior. 

 The smaller capillary, of course, was drawn down farther from the 

 original piece, and so it is conceivable that the internal strains might 

 be enough greater to result in different elastic behavior. In Table I 

 the displacements of the slider of the bridge wire corresponding to 

 the changes of R 9 and R 10, together with the ratio of the displace- 

 ments, are tabulated against the approximate pressure, which was 

 calculated from the comparison of R 10 later against an absolute 

 gauge. The ratio is constant at 1.007, excepting two values, either of 



TABLE I. 

 Comparison of Two Mercury Gauges to show Reproducibility. 



which could be brought to 1.007 by an error of only 0.1 mm. in the 

 slider settings. The ratio of the resistance R 10 to R 9 multiplied 

 into a constant expressing the different linear resistances of the bridge 

 wires is also 1.007. Within the limits of error of the electrical measure- 

 ments, therefore, or within ^ per cent, the mercury resistance gauge 

 may be assumed to be reproducible. 



There is now left only one point in regard to the suitability of the 

 mercury resistance as a secondary standard to be cleared up by the 

 comparison of the mercury with an absolute gauge, namely complete 

 freedom from hysteresis. The absolute gauge is that described in the 



