INTRODUCTION. XXxi 



13. Electrostatic Capacity. — This is the ratio of the numbers for quantity 

 of electricity and difference of potential. The dimensional formula is therefore 



^^^ ^ ^ T — l'p2p— 1 



and the conversion factor /~V^~^ 



14. Resistance of a Conductor. — The resistance of a conductor or elec- 

 trode is the ratio of the numbers for difference of potential between its ends and 

 the constant current it is capable of producing. The dimensional formula is 

 therefore the ratio of those for potential and current or 



MiL4T-^P-i~ 



The conversion factor thus becomes //~^/, and in the ordinary system resistance 

 has the same conversion factor as velocity. 



15. Conductance. — This is the reciprocal of resistance, and hence the dimen- 

 sional formula and conversion factor are respectively L~^TP~^ and lr'^tp~'^. 



16. Conductivity, or Specific Conductance. — This is quantity of electric- 

 ity transmitted per unit of area per unit of potential gradient per unit of time. 

 The dimensional formula is therefore derived from those of the quantities men- 

 tioned as follows : — 



M^L^p-i 



L 



jM^L'T-^Pt 



= L-^TP- 



L 



The conversion factor is therefore l~'^tp~'^. 



17. Specific Resistance. — This is the reciprocal of conductivity as defined 

 in 16, and hence the dimensional formula and conversion factor are respectively 

 L^'T-^P and Pr^p. 



18, Coefficient of Self-induction, or Inductance, or Electro-kinetic In- 

 ertia. — These are for any circuit the electromotive force produced in it by unit 

 rate of variation of the current through it. The dimensional formula is therefore 

 the product of the formulas for electromotive force and time divided by that for 

 current or 



M^L^T-^pi 



MiL^T-^p-i 



X T = LP. 



The conversion factor is therefore Ip, and in the ordinary system is the same as 

 that for length. 



19. Coefficient of Mutual Induction. — The mutual induction of two cir- 

 cuits is the electromotive force produced in one per unit rate of variation of the 

 current in the other. The dimensional formula and the conversion factor are 

 therefore the same as those for self-induction. 



