~I] 
ON PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 
Kxeperiments for improving the Construction of Practical Standards for 
Electrical Measurements.—Ieport of the Committee, consisting of 
Lord RayeiGH (Chairman), Dr. R.'T. GuAzeBRooK (Secretary), 
Lord KEtLvin, Professors W. E. Ayrton, J. Perry, W.G. Apams, 
and G. CarEY Foster, Sir Otiver J. Lopar, Dr. A. MurrHeap, 
Sir W. H. Preece, Professors A. ScHuster, J. A. FLEMING, 
and J. J. Tomson, Dr. W. N. SuHaw, Dr. J. T. Bottomiey, 
Rev. T. C. Firzpatrick, Dr. G. JoHNSTONE STONEY, Professor 
S. P. THompson, Mr. J. Rennig, Principal EK. H. Grirrirus, Sir 
A. W. Ritcxker, Professor H. L. CaLLenpar, and Mr. GEORGE 
MATTHEY. 
APPENDIX PAGE 
I. Notes on the present condition of the work on Electric Units at the 
National Physical Laboratory. By ¥.E.Smira. (vom the Na- 
tional Physical Laboratory) : 
II. Specification for the Practical Application of the "Definition of the In- 
ternational Ampere. (From the National Physical Laboratory). 77 
III. Preparation of the Weston (Cadmium) Standard Cell. (Irom ihe 
National Physical Laboratory). ‘ : : 2 : : F 80 
THE main work during the year has been the completion of the work 
with the ampere balance. The general results are referred to in some 
detail below. The final measurements confirm the opinion expressed in 
last year’s Report that an accuracy of a few parts in 100,000 might 
be reached. It appears that the result is probably accurate to 1 in 
50,000. 
Interim reports on the ampere balance, indicating the progress of con- 
struction, adjustment, and use of the instrument, have been submitted to 
the Association since 1904. 
The Committee are now pleased to report that the balance continues 
to give complete satisfaction. During the past year it has been much 
used for determining the e.m.f. of the Normal Weston Cadmium cell and 
the electrochemical equivalent of silver. A description of the instrument, 
its construction and adjustment, and the results obtained with it in the 
cadmium cell determinations, has been prepared and submitted to the 
Royal Society for publication in its ‘Transactions,’ by Professor Ayrton, 
Mr. Mather, and Mr. F. E. Smith. An account of the work on the 
electrochemical equivalent of silver is well advanced and will be published 
shortly. 
In all some 71 observations have been made on a certain cadmium 
cell (No. 2), using both sets of coils on the balance, and 13 observations 
in which one or other of the two sets was employed. The agreement 
between the individual results obtained with the two sets of coils is 
remarkable, the average difference from the mean amounting only to 6 
parts in a million. The whole series of observations extended over a 
period of nineteen months (September 1905 to April 1907), and during 
that time the coils of the balance were reset five times, No determina- 
tion made has been omitted, except those in which the observations were 
of such a nature that a decision to disregard the result was arrived at 
before its computation. Such occasions were rare. 
