STANDARDS OF RESISTANCE, 1865-1932 



423 



The value is definitely low in some cases, but not low enough to affect 

 the resistance measurements by an appreciable amount. 



In the following paragraphs the significance of the results is considered 

 from several points of view of practical importance. 



Table V. 



Results obtained in 1932 for the British Association 

 Standard Resistance Coils of 1865. 



Values at 16 -00° C. in terms of the B.A. Unit determined by the relation 

 I International Ohm = i -01367 B.A. Units.* 



* In 1892, in accordance with the experiments made at the Cavendish Laboratory, the 

 value of the ohm (10^ C.G.S. units) in B.A.U. was taken as i -01358 B.A.U., and became 

 the unit in general use. In 1903 it was shown by Mr. Smith that this unit was equal to 

 106-291/106-300 international ohms. Thus the international ohm = i 01367 B.A.U. 



(i) The Platinum Coils D and E. 



From an examination of the available data in 1908 Mr. F. E. Smith con- 

 cluded that the platinum coils had probably remained constant since 1867, 

 but that all the other coils had changed. The question of constancy is of 

 such importance that a special study has been made of these two coils. 

 About forty observations were made on each coil in the temperature range 

 15° to 17° C. over a period of four weeks. The results, expressed in terms 

 of the B.A. unit of Table V, could be represented as follows : 



CoilD 

 CoilE 



R/ = I -ooo 12 + 0-003 08 (t — 16-00° C.) 

 R/ ^ I - 000 69 +0-003 06 (t — 1 6 • 00° C .) 



The mean deviation of all the observed points from the values calculated 

 from these equations was 2 - 5 parts in 100,000, which corresponds to a tem- 

 perature difference of 0-008° C. Greater accuracy could not be expected 

 from coils of this construction, and it may be concluded that the coils are at 

 present in a stable condition represented by these equations. The values 

 given in 1908 for the resistance of the coils D and E at i6-o° C. are 8 and 



