LEYDEN JAR. 65 



The charge required to raise the sphere to potential V is ex- 

 pressed by 



It will be seen that in all cases the concentric shell, by increasing 

 the capacity of the sphere, has the effect of diminishing the potential 

 relative to a given charge, or conversely, of increasing the charge 

 relative to a given potential. 



78. CONDENSERS. The presence of the envelope makes it 

 possible to accumulate or condense on the sphere A, a greater 

 quantity of electricity, for the same potential, than if this envelope did 

 not exist. The same effect would be produced upon any conductor 

 A, by the proximity of a second conductor B in connection with 

 the earth, or insulated, but with a charge null, for this conductor 

 diminishes the value of the potential for a given charge. The term 

 condenser is applied to a system of conductors separated by a 

 dielectric, and arranged so as to increase the capacity of one of 

 them to a notable extent. In the present case, the sphere and its 

 envelope constitute what are called the armatures, or coatings of the 

 condenser, the sphere A being the collector, and the sphere B the 

 condenser. 



The condensing force of a condenser is the ratio between the charge 

 of the collector when it forms part of a condensing apparatus, and 

 the charge which it would acquire, for the same potential, if it were 

 distant from any other conductor. It is therefore the ratio of the 

 capacities of the collector in these two circumstances. In the 

 spherical condenser with concentric surfaces, the outer coating of 

 which is in connection with the earth, the value of the condensing 

 force is 



The application of the condensing force presents no interest ; the 

 only magnitude which requires to be known is the capacity of a 

 condenser. 



79. LEYDEN JAR. A Ley den jar is a glass vessel coated outside 

 and inside with metal foil, with the exception of a part near the 

 opening, so that the coatings may not communicate. A conducting 

 rod passing through the neck is connected with the internal coating. 



The system of these two conducting surfaces constitutes an almost 

 closed condenser. 



