ON STANDARDS OF ELECTRICAL RESISTANCE. 111 
Report of the Committee appointed by the British Association 
on Standards of Electrical Resistance. 
The Committee consists of—Professor Wheatstone, Professor Williamson, 
Mr. C. F. Varley, Professor Thomson, Mr. Balfour Stewart, Mr. C. W. 
Siemens, Dr. A. Matthiessen, Professor Maxwell, Professor Miller, Dr. 
Joule, Mr. Fleeming Jenkin, Dr. Esselbach, Sir C. Bright. 
Tue Committee on Electrical Measurements, appointed in 1862, have not 
confined their attention to determining the best unit of electrical resistance, 
the point to which the duties of the Committee of 1861 were nominally re- 
stricted, but have viewed this comparatively limited question as one part only 
of the much larger subject of general electrical measurement. The Committee, 
after mature consideration, are of opinion that the system of so-called abso- 
lute electrical units, based on purely mechanical measurements, is not only 
the best system yet proposed, but is the only one consistent with our present 
knowledge both of the relations existing between the various electrical phe- 
nomena and of the connexion between these and the fundamental measure- 
ments of time, space, and mass. The only hesitation felt by the Committee 
was caused by doubts as to the degree of accuracy with which this admirable 
system could be or had been reduced to practice. 
The measurement of voltaic currents, electromotive force, and quantity 
would offer little difficulty, provided only electrical resistance could be mea- 
sured in absolute units, and for this purpose it would be sufficient that the 
resistance of a single standard conductor should be so determined, since copies 
of this standard could be multiplied at will with any desired precision, and 
from comparison with these copies the absolute resistance of any circuit what- 
ever could be obtained by methods requiring comparatively little skill and 
well known to all electricians. The practical adoption of the absolute system 
was felt therefore to depend on the accuracy with which the absolute resist- 
ance of some one standard conductor could be measured; and while doubts 
existed on this point, it was thought premature to make any extended expe- 
riments on the application of the absolute system to voltaic currents, electro- 
motive force, or quantity. The Committee are happy to report that these 
doubts have been dispelled by the success of the experiments, made for the 
Committee by Professor J. Clerk Maxwell, Mr. Balfour Stewart, and Mr, 
Fleeming Jenkin, according to the method devised by Professor W. Thomson. 
These experiments have been actively prosecuted at King’s College for the 
last five months with continually increasing success, as, one by one, successive 
mechanical and electrical improvements have been introduced, and the various 
sources of error discovered and eliminated. 
The Sub-Committee are confident that considerably greater accuracy can 
yet be obtained by the further removal of slight defects, the importance of 
which only became apparent when the main difficulties had been overcome. 
In order, therefore, to secure the best attainable result, and still further to 
test the accuracy and concordance of the experiments before taking any irre- 
vocable step, the Committee have decided not to issue standard coils at the 
present Meeting; but the results already obtained leave no room for doubt 
that the absolute system may be adopted, and that the final standard of re- 
sistance may be constructed without any serious delay. Over-haste might 
eventually entail corrections as inconyenient as those which would follow an 
arbitrary and unscientific choice of units, and the very experiments made by 
the Sub-Committee prove that the hesitation of many to adopt the absolute 
