RESISTANCE BY A METHOD BASED ON THAT OF LORENZ. 
107 
On the whole, the remaining results in Table I. give the length of the column of 
mercury representing the ohm as greater than 106'25 cm., and while a discussion of 
the methods and apparatus might do much to explain some of the differences, much 
greater detail of the apparatus than is readily accessible is necessary for this to be 
done. 
The ohm and the international ohm differ by about 5 parts in 10,000, and since the 
ampere (10 _1 C.G.S. unit) has been realised with considerable accuracy, we may 
express the electromotive force of the Weston normal cell in absolute measure. The 
value found in 1908 by Ayrton, Mather and Smith at the National Physical 
Laboratory for the E.M.F. of the Weston normal cell in terms of the ampere 
(10 -1 C.G.S. unit) and the international ohm is 1‘01830 volts at 17° C., with a 
probable error of 2 parts in 100,000. The deduced value at 20° C. is 1’01818 volts. 
Since that time measurements have been made by Janet, Laporte, and Jouast # at 
the Laboratoire Central d’Electricite ; by Prof. GuiLLETf and Prof. Pell at, t by 
Haga,| and by Rosa and Dorsey§ at the Bureau of Standards. The results are :— 
Ayrton, Mather, and Smith. 1’01818 
Janet, Laporte, and Jotjast.1’01836 
Guillet .. . 1'01812 
Pell at.1'01831 
Haga. 1’01825 
Rosa and Dorsey.1'01822 
Mean.1’01824 at 20° C. 
These results include the errors of the resistance standards employed as well as the 
errors of the determination of the current in absolute measure. In addition small 
differences existed between the Weston cells. Considering all these circumstances 
the agreement is very remarkable and testifies to the great care taken in the measure¬ 
ments. There appears to be little doubt that the value 1’01824 at 20° C. is correct, 
within 1 part in 10,000. We conclude that the value of the cell in volts (10 8 C.G.S. 
units) is 1'0188± ’0001 at 20° C. This value may serve for the present for those 
engaged in absolute measurements. 
Section 24.— Conclusions. 
From the measurements recorded in the previous sections, we conclude that the 
instrument we have described may be used for absolute measurements of resistance 
* ‘Bull, de la Soc. Internat. des Electriciens’ (2), vol. 8, p. 459, 1908, and ‘ Comptes Rendus,’ 153, 
p. 718, 1911. 
t ‘ Bull, de la Soc. Internat. des Electriciens,’ 1908. 
1 ‘ Konink. Akad. Wetensch. Amsterdam Proc.,’ p. 587, 1910. 
.§ ‘Bull. Bureau of Standards,’ vol. 8, p. 269, 1912. 
p 2 
