614 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
A similar comparison is also afforded by the last column on Table XIII., and here 
there is almost exact agreement between our results on November 1 4 and the Board 
of Trade measurements on March 9. 
The standards would appear to be exactly equal, but these observations hardly 
deserve as much weight as the others, for the temperature of the large H cells is not 
very easy to be sure of. 
It would seem then the Board of Trade standards are lower in E.M.F. than our 
standard by, possibly, one or two of our units, that is, by about ‘0003 volt. This 
clearly is very small. The Board of Trade standards are a set of 72 cells constructed 
by Dr. Muirhead. These cells are from time to time compared against each other, and 
Mr. PtENNiE states that the greatest variation among them is less than ‘00068 volt, 
that is, distinctly under three of our units. The cells used were known to be good 
average cells. 
Dr. Schuster’s cell No. 97 was taken to London on December 21, and on 
January 11 it was compared, with the following results given by Mr. PtENNiE. 
At 8 o, 0 C. the E.M.F. of B.T. 822/35 exceeds that of Schuster’s cell by 0‘00021 volt. 
At 8°T C. the excess was 0‘00017 volt. 
At 8 0, 3 C. the E.M.F. of B.T. 822/34 was less than that of Schuster’s cell by 
0‘00005 volt. 
Thus Schuster’s cell lies between the two Board of Trade standards, and falls 
short in E.M.F. of the mean of the two by less than one of our units. 
§ 26. The Temperature Coefficient of the Cells. 
We have also made some experiments with a view of investigating the temperature 
coefficient of our cells. 
It has already appeared from Table II. extending over a range of temperature 
from 0° to 18° that our more important cells, including the standard Itayleigh 1, have 
practically the same coefficient. When we were engaged in the experiments in 
August we did not expect them to be continued so long, and therefore a cell was 
fitted up which could be packed in ice. 
It Avas a cell of the ordinary form, but contained a delicate thermometer, the bulb 
of which was in the paste. The cell was placed inside a long test tube, packed with 
glass-wool and asbestos; the thermometer passed through a cork closing the test 
tube. The stem of the thermometer was so long that most of its graduations were 
outside the cork. It could be read, therefore, without seriously disturbing the cell 
when packed in ice. With this cell a number of measurements were taken. 
The results of these are given in the accompanying Table XIV”. 
