80 



MR. F. E. SMITH ON THE CONSTRUCTION OF 



It is convenient at this point to give a summary of the data accumulated. In the 

 following table is set forth : 



(1.) The length L of the standard at 0'0 C. 



(2.) The theoretical length I for 1 international ohm, assuming the conical 



correction to be unity. 



(3.) The value of the conical correction for each tube. 

 (4.) The theoretical length for 1 international ohm, the conical correction having 



been applied. 

 (5.) The calculated resistance at 0'0C. of the mercury column occupying the tube. 



TABLE IV. 



The tubes M, V, X, Z, G and S were intended to have a resistance of approximately 

 one ohm when fitted up in a certain manner. (See Erection Method I.) The 

 remainder have a resistance approximating to one ohm when erected by Methods II. 

 and III. 



Erection of Standards for Resistance Measurements. 

 Three methods of erection have been employed. They are as follows : 



Method I. The standard was so erected as to enable the resistance to be measured 



of that mercury column contained between the two plane termini of the tube. 



Method II. The erection was such as enabled the resistance to be measured 



between two points situated without the plane termini referred to above, 



thus introducing " end corrections " to the tube. 



Method III. The "end corrections" were necessarily introduced as in Method II. 

 The resistance, however, was most conveniently measured by the Carey 

 Foster Bridge. (Methods I. and II. do not admit of accurate measurement 

 of the standards in this way.) 



Before describing these methods it is necessary to give some explanation of: 



