74 On the Value of some Mercury Resistance Standards. 



And then we find as the values of the tubes in Legal Ohms: 



Benoit. R. T. G. 1891. 



37 1-00045 1-00033 



39 -99954 -99959 



and these numbers show an extremely close agreement, thus 

 proving that the resistance of a column of mercury 100 cm. 

 in length, 1 sq. mm. in section, as given in this indirect way 

 by Benoit's experiments, is very close to the value *9535 

 B.A. unit. 



In my previous paper * are given some values for the change 

 of resistance of mercury with temperature. On January 3 I 

 observed the resistances of the tubes Nos. 37 and 39 at a 

 temperature of 12°'9 C. The results were : — 



Resistance at 12° -9. 



37 1-02254 



39 1-02193 



From these we get as the values of the coefficients per 1° C, 

 •000875 and -000870 respectively. Thus the mean coefficient 

 between 0° and 13° is '000872. This agrees well with the 

 values found in 1885, the mean value between 0° and 10° 

 being -000861, and between 0°and 15° '000879. From these 

 we have as the value between 0° and 13°, '000872. 



Benoit f and Strecker J give higher values than the above, 

 Strecker's value between 0° and 13° being -000906. 



In the paper on the specific resistance of mercury, Phil. 

 Trans. A, 1888, I have called attention to some of the conse- 

 quences of this difference. The value of the coefficient be- 

 tween 0° and 10° found by Mr. Fitzpatrick and myself in 

 1888 was -000876. Kohlrausch § and Strecker || find as the 

 values for the resistance of mercury in B.A. units, '95338 and 

 •95334 ; these are less than the value found by Salvioni, 

 Hutchinson, Wuilleumeier, and myself, and the difference is, 

 I believe, mainly due to the uncertainty in the temperature 

 coefficient. They both worked with their tubes in a bath at 

 about the temperature of the room, and reduced their results 

 to 0° by the use of Strecker's coefficient. The mean tem- 

 perature adopted by Kohlrausch was 10°, he puts 



a = — ^° 

 1-00904' 



* Phil. Mag. October 1885. 

 t Benoit, Journal de Physique, 1884. 

 \ Strecker, Wied. Annalen, vol. xxv. p. 475. 



§ Kohlrausch, Abhand. der K. bayer. Akad. der Wiss. ii. CI. xvi. 

 Bd. iii. Abt. 



|| Strecker, Wied. Annalen, vol. xxv. p. 475. 



