348 



Mr. R. T. Grlazebrook's Comparison of 



however, my apparatus allowed me to measure the resistance 

 of the contact-tubes with all the accuracy I desired, the first 

 method was the more convenient, as it necessitated fewer obser- 

 vations. 



The comparisons were made both with the original standards 

 of the British Association — B.A. Units — and also with the 

 Legal-Ohm Standards of the same, recently constructed for 

 me by Messrs. Elliott Bros., taking as a basis the value 

 for the resistance of mercury in terms of the B.A. unit 

 adopted by the British-Association Committee. According 

 to this, 



1 Legal Ohm= 1-0112 B.A.U. 



The three mercury tubes Nos. 37, 38, 39, sent by M. Benoit, 

 were compared. Between two observations of resistance the 

 mercury was occasionally drawn through the tubes by con- 

 necting the cups alternately to the air-pump. I hoped in this 

 manner to displace any very small air-bubble or particle of dust 

 which might have got lodged in the tube. In the final set of 

 observations recorded below, it will be seen that no appreciable 

 change in the resistance was detected by this precaution. I 

 therefore suppose the tubes to have been properly filled. 



In some earlier observations, which will be referred to again 

 shortly, variations of considerable amount were produced by 

 passing the mercury through. In the tables below the values 

 of the resistances which were found by comparison with the 

 B.A.U., and reduced to Legal Ohms by means of the known 

 relation between the two, are denoted by an asterisk. 



Table I. 



Tube No. 37. Value given by Benoit, 1-00045. 



Date and Method of Treatment. 



Value in L. Ohms. 



April 13, 10 a.m 



•99991* 



•99987 

 •99998 



•99997 



•99998 



•99996 



•99979 

 •99976* 



10.30 



11.55 



1pm 1 After passing the 1 

 \ mercury through. J 

 April 14 



April 14 { After P a ^ in S ^ e \ 



r I mercury through. J 



April 15 



April 15 





Mean value 



•99990 





