ol 
ON STANDARDS OF ELECTRICAL RESISTANCE. 161 
which the magnetic action is due, we shall have the repulsion of two 
mm 
7? 
poles = , Where m m' are the two poles, « the density of the magnetic 
medium, and r the distance. Now a density is a mass, M,, divided by L’, the 
unit of volume. Hence the dimensions of m are at or if we can 
measure the density of the magnetic medium in the same unit of mass as that 
employed for other purposes, the dimensions of m would be simply = Those 
of H would then be = or a velocity. 
If we suppose the density of the magnetic medium to be taken account of 
in the electromagnetic units, their dimensions become 
Quantity of electricity. .Q=L’, or equivalent to an area. 
2 
Strength of current ....C =a 
Electromotive force .. . aS 
: M 
f conductor R= 
Resistance of conductor Fal 
_ The electromagnetic unit of quantity of electricity is equal to the electro- 
static unit multiplied by a certain velocity, depending on the elasticity of the 
magnetic medium, and proportional or probably equal to the velocity of pro- 
pagation of vibrations in it. Hence the dimensions of 
Electrostatic quantity ........ qg=LT 
Electrostatic current.......... c=L 
Electrostatic electromotive force e= 8 
IRESISLATICE, 4.33 5.%, «eierh Meee a oti a 
As we have no knowledge of the density, elasticity, &c., of the magnetic 
medium, we assume it as having a standard state in common air ; and sup- 
posing all measurements to be made in air, the original table of dimensions is 
sufficient for expressing measurements made according to one system in terms 
of any other system. 
51. Magnitude of Units and Nomenclature.—In connexion with the system 
of measurement explained in this treatise, two points hitherto unmentioned 
deserve attention—first, the absolute magnitude of the units, and secondly, 
the nomenclature. 
_ The absolute magnitude is in most cases an inconvenient one, leading to 
the use either of exceedingly small or exceedingly large numbers. Thus the 
units of electromagnetic resistance and electromotive force and quantity, and 
of electrostatic currents, are inconyeniently small; the unit of electrostatic 
resistance is inconveniently large. Decimal multiples and submultiples of 
these units will therefore probably have to be adopted in practice. The 
choice of these multiples and submultiples forms part of the business of the 
Committee. 
The nomenclature hitherto adopted is extremely defective. In referring 
to each measurement, we have to say that the number expresses the value in 
electrostatic or electromagnetic absolute units: if a multiple is to be used, this. 
Poa will also have to be named; and further, the standard units of length,” 
63. M 
