1888.] 



On the Specific Resistance of Mercury, 



379 



X. M On the Specific Resistance of Mercury." By R. T. Glaze- 

 brook, M.A., F.R.S., Fellow of Trinity College, and T. C. 

 FiTZPATRiCK, B.A., Fellow of Christ's College, Demonstrators 

 in the Cavendish Laboratory, Cambridge. Received June 

 19, 1888. 



(Abstract.) 



The paper contains an account of experiments made to determine 

 the value of the resistance of a column of mercury, 1 metre long and 

 1 sq. mm. in cross section, in terms of the B.A. unit. The method 

 employed differed very slightly from that of Lord Rayleigh and 

 Mrs. Sidgwick ('Phil. Trans.,' 1883). Tubes of about 1, 2, and 

 3 sq. mm. in cross section were calibrated a.nd filled with mercury. 

 They were then immersed in melting ice, and their resistance com- 

 pared with that of the B.A. standards, using Carey Foster's method 

 and the B.A. bridge. The length of the mercury column, occupying 

 nearly the whole of the tube, was measured, and the mass of the same 

 determined. From this the average cross section is obtained, and hence 

 the value of r, the resistance of a column 1 metre long, 1 sq. mm. in 

 cross section. The mercury used to find the cross section was with 

 few exceptions that which had been employed in finding the resistance. 

 The results of the measurements are given in Table I. 



In the table, Column 1 gives the number of the tube, Column 2 the 

 number of the observation. L is the length of the tube, and a the 

 mean radius of the cross section, R the observed resistance in B.A. 

 units. The mean value of r found from the three 1 mm. tubes is 

 0*95354 B.A. units. The other four tubes of one-half and one-third 

 units respectively lead to the value r = 0*95344 B.A. units. The 

 difference between the two is considerable, and reasons are given for 

 assigning more weight to the first value. 



For an account of the experiments and of the small precautions 

 necessary to secure accuracy, reference must be made to the paper. 



Table II gives a list of the various values which have been found 

 for r with the lengths of the column of mercury which, according to 

 the different observers, has a resistance of 1 ohm (10 9 C.G.S. units of 

 resistance). In combining our own observations we have assigned 

 weights to the various tubes inversely proportional to their diameters, 

 and we find as our final value 



r = 0-95352. 



VOL. XLIV. 



