352 



Mr. R. T. Glazebrook's Comparison of 



and it is only the small portions of the tubes which lie within 

 the cups which will be at the higher temperature. 



The necessity of using the somewhat complicated con- 

 necting pieces is also a great drawback to the practical use- 

 fulness of the mercury standards. I hope shortly to carry 

 out some experiments on the permanence of the contact be- 

 tween mercury and amalgamated platinum. Contact-pieces of 

 platinum with their end amalgamated with mercury would 

 be easier to work with, and should give consistent results. 



I have also made some observations on the variation of the 

 resistance of mercury with temperature. 



The formula quoted above from Benoit is given by Mascart, 

 Nerville, and Benoit as determined from experiments between 

 0° and 100°. 



It is 



R,= Ro(l + -0008649* + -00000112* 2 ). 



According to Strecker, 



B* = R (l + '000900* + -00000045* 2 ). 



This is derived from observations at 0°, 10°, 15°, and 20°. 



Lorenz finds that between 0° and 27°'32 his experimental 

 results agree with the formula 



R* = Bo(l + -00090130; 

 and from 8°'32 to 35°'31 with 



B*=Eo(l+ 0009160- 

 While Siemens and Halske give 



R,=R (1 + -0008523* + -000001356* 2 ). 



I made observations on the two tubes, Nos. 37 and 39, 

 determining their resistances at temperatures of about 0°, 5°, 

 10°, and 15°; and the results of the observations show that the 

 average change for low temperatures is less than that given 

 by the above formulae. Thus, if we call (R f —R )/R * the 

 average change between temperatures * and 0, the values, as 

 found from my experiments and as calculated by the formulae 

 of Siemens and Benoit, are as given below. 



Average change 

 between 



Siemens and 

 Halske. 



Benoit. 



B. T. G-. 



o o 

 5 and 



10 „ 



15 „ 



•000858 

 •000865 

 •000872 



•000870 

 •000876 

 •000881 



•000834 

 •000861 

 •000879 



