ON STANDARDS. OF ELECTRICAL RESISTANCE. 129 
‘These four very simple examples of the use of Weber’s and Thomson’s 
system might be multiplied without end, but it is hoped that they will suffice 
to give some idea of the range and importance of the relations on which it 
depends to those who may hitherto not have had their attention directed to 
the dynamical theory. 
No doubt, if every unit were arbitrarily chosen, the relations would still 
exist in nature, and, by a liberal use of coefficients experimentally determined, 
the answer to all the problems depending on these relations might still be 
calculated; but the number of these coefficients and the complication re- 
sulting from their use would render such an arbitrary choice inexcusable. 
A large number of units of resistance have from time to time been proposed, 
founded simply on some arbitrary length and section or weight of some given 
material more or less suited for the purpose ; but none of these units in any 
way possessed what we have called the second and third requisite qualities, 
and could only have been accepted if the unit of resistance had been entirely 
isolated from all other measurements. We have already shown how far this 
is from being the case; and the Committee consider that, however suitable 
mercury or any other material may be for the construction or reproduction of 
a standard, this furnishes no reason for adopting a foot or a metre length of 
some arbitrary section or weight of that material. 
Nevertheless it was apparent that, although a foot of copper or a metre of 
mercury might not be very scientific standards, they produced a perfectly 
definite idea in the minds of even ignorant men, and might possibly, with 
certain precautions, be both permanent and reproducible, whereas Weber’s 
unit has no material existence, but is rather an abstraction than an entity. 
In other words, a metre of mercury or some other arbitrary material might 
possess what we have called the first, fourth, and fifth requisite qualities, to a 
high degree, although entirely wanting in the second and third. Weber’s 
system, on the contrary, is found to fulfil the second and third conditions, but 
is defective in the fourth and fifth; for if the absolute or Weber’s unit were 
adopted without qualification, the material standard by which a decimal 
multiple of convenient magnitude might be practically represented would 
require continual correction as successive determinations made with more and 
more skill determined the real value of the absolute unit with greater and 
greater accuracy. Tew defects could be more prejudicial than this continual 
shifting of the standard. This objection would not be avoided even by a 
determination made with greater accuracy than is expected at present, and 
was considered fatal to the unqualified adoption of the absolute unit as the 
standard of resistance. 
- It then became matter for consideration whether the adyantages of the 
arbitrary material standard and those of the absolute system could not be 
combined, and the following proposal was made and adopted as the most 
likely to meet every requirement. It was proposed that a material standard 
should be prepared in such form and materials as should ensure the most 
absolute permanency; that this standard should approximate as nearly 
as possible in the present state of science to ten millions of aneine , but 
seconds 
that, instead of being called by that name, it should be known simply as the 
unit of 1862, or should receive some other simpler name, such as that proposed 
by Sir Charles Bright and Mr. Latimer Clark in the paper above referred 
to; that from time to time, as the advance of science renders this possible, 
xa 7 Sahaad between this unit of 1862 and the true ten millions of 
é K 
