PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 95 
Experiinents for improving the Construction of Practical Standards for 
Electrical Measwrements.—Report of the Committee, consisting of 
Lord RayLetaH (Chairman), Dr. R. T. GLazeBrooK (Secretary), 
Lord Krtvin, Professors W. E. Ayrton, J. Perry, W.G. ADAms, 
and G. Carey Foster, Sir Otiver J. Lopar, Dr. A. MuIrHEap, 
Sir W. H. Preece, Professors A. ScuusterR, J. A. FLEMING, 
and J. J. THomson, Dr. W. N. SHaw, Dr. J. T. BorroMLey, 
Rey. T. C. Fitzpatrick, Dr. G. JoHNSTONE STONEY, Professor 
S. P. Tuompson, Mr. J. RENNIE, Principal KE. H. Grirriras, Sir 
A. W. Ricker, Professor H. L. CaLLenpar, and Mr. GEORGE 
MarTraey. 
APPENDIX— On the Preparation of a Cadmium Cell. By ¥. E. SMITH. 
(From the National Physical Laboratory) page 98 
Tue Committee are glad to report that satisfactory progress has been 
made during the year with the Ampere Balance. 
The weighing mechanism was taken over from the maker shortly after 
the last meeting of the Association and the work on the coils completed 
at the National Physical Laboratory. The labour involved in insulating 
the two wires on the large cylinders was very great. Each wire consists 
of about ninety turns of about 103 centimetres circumference. Thus each 
wire is about 93 metres in length, and the two are along their whole 
_length about one-tenth of a millimetre apart. In the coils as finally set 
up the insulation resistance between these two wires is measured in 
thousands of megohms, and is thus amply sufficient. 
The cost of the balance has amounted to 302/. 6s., the excess over 
the 300/. granted for the purpose being met out of the general fund at the 
disposal of the Committee. 
Calculations of the force to be expected between the coils when 
carrying one ampére have been made by Mr. Mather and Mr. F. E. Smith, 
of the National Physical Laboratory, and are in close agreement. 
The designs from which the balance has been made are the work of 
Mr. Mather, and originally it was contemplated that the balance would 
be set up at the City and Guilds Central Institute in Exhibition Road. 
At a meeting of the Committee held on March 31, 1905, however, this 
decision was modified, and the following minute agreed to :— 
That the Ampére Balance remains for the present at the National 
Physical Laboratory, and that a determination of the ampére be made 
with it there under the supervision of Professor Ayrton and Mr. Mather, 
steps being taken to connect closely with the determination and with any 
notification of the results the names of the late Professor J. V. Jones, 
_ Professor Ayrton, and Mr. Mather, to whom the design of the instrument 
is entirely due. 
Accordingly the balance has been set up at the National Physical 
Laboratory and a number of preliminary tests have been made. Par- 
ticulars of some of these follow. 
Ampere Balance.—The weighing mechanism of the balance was 
erected by Mr. L. Oertling at the National Physical Laboratory in 
March of the present year, and the electrical equipment was completed 
