134 REPORTS ON THE STATE OF SCIENCE.—1913, 
that the Council have taken over the volume as a publication of the 
Asscciation. 
During the year the death of Mr. G. Matthey, F.R.S., has deprived 
the Committee of a valued colleague. His ready help was always 
given when questions dealing with the purity of the metals required 
for the work of the Committee were under discussion. 
In 1861 the first work to be undertaken by the Committee was the 
realisation of the absolute unit of resistance. In 1882, 1883, 1888, 
1894, and again in 1897, other measurements were made by members 
of the Committee, and in this their last Report they are pleased to 
be able to announce a further development. The new Lorenz apparatus 
at the National Physical Laboratory is now complete, and measure- 
ments of resistance can be made by means of it with an uncertainty 
of not more than a few parts in 100,000. During the present year 
a large number of such measurements have been made, and the results 
obtained are now being prepared for publication. 
A satisfactory feature of the machine is that it can be used at 
all times for absolute measurements, and the plans adopted for the 
re-determination of the dimensions of the coils ensure an accuracy in 
the future as great as that obtained in the recent measurements. The 
nominal values of the resistances measured are 0°001, 0°002, and 
0°01 ohm. As an instance of the care taken, it may be mentioned 
that the dimensions of the coils have been measured with a current 
flowing through them, and the radius of a disc 53 cm. in diameter 
has been determined within 0°01 mm. when running at 1,200 revolu- 
tions per minute. Electrical methods of setting the coils parallel and 
coaxial with the shaft proved to be more sensitive than the usual 
methods, and a Wheatstone bridge with a condenser in one arm proved 
to be the most sensitive indicator of constancy of speed. This instru- 
ment, together with the Ayrton-Jones current balance, enables the 
fundamental electrical units to be realised with an accuracy sufficient 
for all present purposes. It is hoped to re-wind the coils of the current 
balance and leave them uncovered with paraffin wax so that their 
dimensions may be determined at any time. 
The Committee are pleased to report that the original rotating-coil 
apparatus, designed by Lord Kelvin in 1861, is in good condition, 
and steps are being taken for its inclusion in the Science Museum, 
South Kensington. Some rough measurements of resistance were 
made by the apparatus in the spring of this year, and the coils used 
by Lord Rayleigh in 1882 were also experimented with. An account 
of the apparatus is given in the Secretary’s ‘ Kelvin’ Lecture to the 
Institution of Electrical Engineers. 
A statement on international comparisons of resistances and 
standard cells was included in last year’s Report and _ sufficiently 
indicates the arrangements that have been made for the maintenance 
of constant electrical standards in the future. The Committee regard 
these arrangements as satisfactory. They do not ask for reappoint- 
ment. 
