148 REPORT—1863. 
The material standard for electromotive force derived from electromagnetic 
phenomena would naturally be a conductor of known shape and dimensions, 
moving in a known manner in a known magnetic field. Such a standard as 
this would be far too complex to be practically useful: fortunately a very 
simple and practical standard or gauge of electromotive force can be based 
on its statical effects, and will be described in treating of those effects (Part 
IV. 43). A practical standard for approximate measurements might be 
formed by a voltaic couple, the constituent parts of which were in a standard 
condition. It is probable that the Daniell’s cell may form a practical stand- 
ard of reference in this way, when its value in electromagnetic measure is 
known. This value lies between 9 x 107 and 11 x 10". 
Resistances are compared by comparing currents produced in the several 
conductors by one and the same electromotive force. The unit resistance, 
determined as in Appendix D, will be represented by a material conductor ; 
simple coils of insulated wire compared with this standard, and issued by the 
Committee, will allow any observer to measure any resistance in electro- 
magnetic measure. 
Part [V.—Measvrement or Execrric Puenomena By Sratican Errecrs. 
33. Electrostatic Measure of Electric Quantity.—By the application of a 
sufficient electromotive force between two parts of a conductor which does 
not form a circuit, it is possible to communicate to either part a charge of 
electricity which may be maintained in both parts, if properly insulated (14). 
With the ordinary electromotive forces due to induction or chemical action, 
and the ordinary size of insulated conductors, the charge of electricity in 
electromagnetic measure is exceedingly small; but when the capacity of the 
conductor is great, as in the case of long submarine cables, the charge may 
be considerable. By making use of the electromotive force produced by the 
friction of unlike substances, the charge or electrification even of small bodies 
may be made to produce visible effects. The electricity in a charge is 
not essentially in motion, as is the case with the electricity in a current. 
In other words, a charge may be permanently maintained without the per- 
formance of work. Electricity in this condition is therefore frequently 
spoken of as statical electricity, and its effects, to distinguish them from 
those produced by currents, may be called statical effects. The peculiar pro- 
_perties of electrically charged bodies are these :— 
1. When one body is charged positively (14), some other body or bodies 
must be charged negatively to the same extent. 
2. Two bodies repel one another when both are charged positively, or both 
negatively, and attract when oppositely charged. 
3. These forces are inversely proportional to the square of the distance of 
the attracting or repelling charges of electricity. 
4. If a body electrified in any given invariable manner be placed in the 
neighbourhood of any number of electrified bodies, it will experience a force 
which is the resultant of the forces that would be separately exerted upon it 
by the different bodies if they were placed in succession in the positions 
which they actually occupy, without any alteration in their electrical con- 
ditions. 
From these propositions it follows that, at a given distance, the force, f, 
with which two small electrified bodies repel one another is proportional to 
the product of the charges, g and q,, upon them, But when the distance 
