Electricity for public schools and colleges . PACITIES 12 various other dielectrics were used. In this way he obtained theinductive capacity of these materials as compared with that of thestandard glass. Then he determined the ratio borne by the inductivecapacity of this glass to that of air, and so obtained finally the specificinductive capacity {see definition) of the dielectrics employed. In fig. i. D represents in section the condenser in which the dielec-tric was the substance whose specific inductive capacity was represents one or more standard condensers. The upper plates ofbo
Electricity for public schools and colleges . PACITIES 12 various other dielectrics were used. In this way he obtained theinductive capacity of these materials as compared with that of thestandard glass. Then he determined the ratio borne by the inductivecapacity of this glass to that of air, and so obtained finally the specificinductive capacity {see definition) of the dielectrics employed. In fig. i. D represents in section the condenser in which the dielec-tric was the substance whose specific inductive capacity was represents one or more standard condensers. The upper plates ofboth were charged from the same source, and therefore to the samepotential ; and the under plates were put to earth or were at zeropotential. If the charges upon the upper plates were + a and + brespectively, then those upon the lower plates would be (very nearly)- a and - b respectively ; the charges on the upper plates exceedingthose on the lower by negligible free charges. When the condensers were charged, matters were arranged as i in fig-. n. It is not difficult to see that if a and b were equal, then thecharges + a and— b would (verynearly) neutraliseone another. Thewire connectingthese plates com-municated with adelicate electro-scope : and thusit could be seen ^^^^- ^=- • E^^- whether there was neutralisation or no. Standard condensers weregrouped together until such neutralisation was observed. When this wasthe case the capacity of G was equal to that of D. For, by our formula, a = K(V-Vo),^ = K (V-Vo) where K and K were the capacities of the two condensers D and Grespectively. And since (V-Vo) was the same for both, it followedthat a could only equal b if K = K. Then, from a knowledge ofthe dimensions of the two condensers, Cavendish determined the ratioof the two inductive capacities, or the ratio that would have existedbetween the charges a and b had the condensers been similar in allrespects save in the nature of the dielectric In somewhat the same manner he comp
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