150 MR. A. NORMAN SHAW: A DETERMINATION OF THE ELECTROMOTIVE 
and accuracy of the deflection observations. There still remained, however, an 
appreciable effect due to imperfect elasticity of the wires, and a good deal of time 
was spent in selecting a suitable suspension. With the round wires ultimately 
adopted, and subsequently employed by Mr. Shaw, the effect amounted, as nearly as 
I could estimate, to 3 parts in 10,000 under the conditions of the deflection experiments. 
It appeared to me at the time that the effect was largely due to the sharp bending of 
the wire at the four points where it was rigidly clamped. I accordingly prepared a 
rolled strip of equal carrying capacity to take the place of the round wire with the 
object of reducing the creep. This would probably have proved effective, but it was 
considered inadvisable to disturb the suspension at the time, when half the observations 
were completed, seeing that the correction was so small in relation to the order of 
accuracy then contemplated. The exact study of this suspension since carried out by 
Mr. Shaw, has made it possible to determine the correction to a much higher order of 
accuracy, so that this last objection to the deflection method has been removed. 
Now that Mr. Shaw has repeated the observations and revised the whole theory of 
the experiment with such minute care and accuracy, I feel sure that the results should 
take rank among the best determinations of recent years, and should possess special 
interest as an independent determination on account of the many radical differences 
of procedure involved. At the same time I hope that Mr. King’s share in the 
research as a student in reconstructing the apparatus and getting it into working 
order, and his generosity in providing the means for the ultimate completion of the 
observations will not be forgotten. 
I. Introduction. 
Accounts of several absolute determinations of current have been published in recent 
years, and it does not, therefore, appear necessary to present an extended introduction 
to the subject. The results of the most recent determinations of the electromotive 
force of the Mean Weston Normal Cell are as follows :— 
1908, Ayrton, Mather, and Smith* * * § . . 
1908, GuilletI. 
1908, Pell at!. 
1908-10, Janet, Laporte, and Jouanst§ 
1910, Haga and Boerema||. 
1912, Bosa, Dorsey, and MillerII . . 
1'01818 semi-absolute volts at 20° C. 
1'01812 
1'01831 
1'01836 
1'01825 
1-01822 
?? 
J5 
5 5 
* Ayrton, Mather, and Smith, ‘Phil. Trans.,’ A, vol. 207, pp. 463-544, 1908. 
f Guillet, ‘ Bull, de la Soc. Int. des Elect.,’ 2, vol. 8, pp. 535-561, 1908. 
1 Pellat, ‘Bull, de la Soc. Int. des Elect.,’ 2, vol. 8, pp. 573-633, 1908. 
§ Janet, Laporte, and Jouanst, ‘Bull, de la Soc. Int. des Elect.,’ 2, vol. 8, pp. 459-522, 1908; also 
(II.), vol. 10, p. 482, 1910. 
|| Haga and Boerema, ‘ Kon. Akad. Wetensck. Amsterdam, Proc.,’ p. 587, 1910. 
H Rosa, Dorsey, and Miller, ‘ Bull. Bur. of Stan.,’ vol. 8, p. 269, 1912. 
