PHYSICS: ROSA AND VINAL 
59 
but the experiments have led to concordant results for the mass of this 
carrier. In free space the mass of the electron may be taken as 1/1845 
times that of the hydrogen atom, while we have found for the carrier 
in copper 1/1660, in aluminium 1/1590, and in silver 1/1540. We 
hope to construct a new apparatus which will increase the accuracy 
of measurement enough so that we can make certain whether the mass 
of the carrier is really larger in metals than in free space. 
A more complete account of these experiments has been accepted by 
the Physical Review for publication. 
THE SILVER VOLTAMETER AS AN INTERNATIONAL STANDARD 
FOR THE MEASUREMENT OF ELECTRIC CURRENT 
By E. B. Rosa and G. W. Vinal 
U. S. BUREAU OF STANDARDS. WASHINGTON. D. C. 
Read before the Academy, November 14, 1916 
The International Electrical Conference which met in London in 
1908 adopted the ampere as the second fundamental electrical unit, 
the ohm being the first, and defined the international ampere in terms 
of the electrolytic deposit of silver in the silver voltameter. At the 
time of this conference it was the opinion of the delegates from this 
country that the volt should have been chosen in place of the ampere, 
because the standard cell was more reproducible than the silver volta- 
meter and was the means then as now actually employed (in conjunction 
with the ohm) for measuring the ampere by the drop in potential method. 
The decision of the conference was, however, accepted as final, and re- 
searches were undertaken in several different countries, and particularly 
in this country, with the aim of making the voltameter worthy to bear 
the responsibility imposed upon it by the London Conference. The 
purpose of this paper is to give briefly the most important results that 
have been obtained and to show the remarkable agreement of the meas- 
urements recently made in the national laboratories of several different 
countries of the electromotive force of a Weston normal cell, in terms 
of the international volt as officially defined. This agreement is due 
to the fact that great advances have been made in our knowledge of 
the silver voltameter in recent years; and although no adequate speci- 
fications have been formally adopted, the methods followed by recent 
investigators have agreed in essential particulars, although differing 
in details. 
No concrete standard for the ampere, corresponding to the column 
