10 _ SCIENCE 
electromotive forces, and the value of 
which is fixed in terms of the international 
ohm and the international ampere. These 
conerete standards were defined by the 
Chicago Electrical Congress of 1893. The 
principal countries of the world did not, 
however, adopt the Chicago specifications 
and numerical values unchanged, so that 
the international uniformity hoped for was 
not altogether realized. As the precision of 
electrical measurements increased and there 
came a demand for greater accuracy in 
electrical instruments, the old specifications 
became inadequate, and the differences in 
numerical values between different coun- 
tries became more and more annoying. 
After attention had been drawn at St. 
Louis in 1904 to the need of a new inter- 
national conference for the purpose of se- 
curing improved specifications for the con- 
erete electrical standards and uniform 
numerical values for the same, and after a 
preliminary conference at Charlottenburg 
in 1905, in which the program for such an 
international conference was carefully 
considered, the conference was called by 
Great Britain, and met in London in Oc- 
tober, 1908. Although considerable atten- 
tion has been given to the subject of abso- 
lute electrical measurements and the prep- 
aration of the concrete electrical standards 
in the fifteen years between 1893 and 1908, 
it was found at the London Conference im- 
possible to formulate complete specifica- 
tions for the three primary electrical quan- 
tities, and impossible to agree upon a satis- 
factory value for the Weston normal cell, 
which latter was adopted at London in 
place of the Clark cell, as the official stand- 
ard for expressing the value of the inter- 
national volt. The discussion at the Lon- 
don Conference brought out clearly the 
inadequacy of a bulky international con- 
ference, sitting for a week or ten days once 
or twice in a generation, as a tribunal for 
teen 
[N.S. Von. XXXV. No. 888 
settling wisely such technical questions as 
are involved in the specifications of elec- 
trical standards and fixing the values of 
the standard cells so that it would satisfy 
Ohm’s law. It was recognized that this 
law could not be repealed or ignored, even 
by an international conference, and the 
best that could be done, therefore, was to 
choose a provisional value for the Weston 
cell (1.0184 volts at 20°) and to leave to 
an International Committee on Electrical 
Units and Standards, established by the 
London Conference for the purpose, the 
task of carrying on the investigations, com- 
pleting the specifications, and finding a 
new and more precise value of the stand- 
ard cell. This committee consisted of fif- 
members and five associate mem- 
bers, representing eleven different coun- 
tries, and during the three years that 
have elapsed since the London Confer- 
ence it has encouraged investigations in 
the direction indicated, and has partly 
accomplished its task. While the com- 
mittee as a whole has acted in the matter, 
the experimental work has been done 
chiefly by the national standardizing lab- 
oratories of England, France, Germany 
and the United States, and in this work the 
Bureau of Standards has been active. 
It might appear that three years is 
ample time in which to settle all the ques- 
tions necessary to the satisfactory com- 
pletion of the work left undone by the Lon- 
don Conference, and so it would be if a 
reproducibility of one one-hundredth of 
one per cent. in the standards were 
deemed sufficient. But when we recall the 
constancy of the standards of length and 
mass, and the regularity of the earth as a 
standard timepiece, we can not be content 
with our concrete standards of resistance 
and electromotive force so long as uncer- 
tainties exist as great as a thousandth of 
one per cent. As the demands for greater 
