The London, Edinburgh and Dublin philosophical magazine and journal of science . enser, theother plate of which is connectedwith D. Thus, when P is in con-tact with S the condenser will becharged, and until it is fully charged electricity will flow into it from the battery : this will producea momentary current through the various arms of the the moving piece P is in contact with R, the two platesof the condenser are connected, and the condenser will dis-charge itself through D R ; and as the resistance of D E isinfinitesimal in comparison with the resistance in any othercircuit, t
The London, Edinburgh and Dublin philosophical magazine and journal of science . enser, theother plate of which is connectedwith D. Thus, when P is in con-tact with S the condenser will becharged, and until it is fully charged electricity will flow into it from the battery : this will producea momentary current through the various arms of the the moving piece P is in contact with R, the two platesof the condenser are connected, and the condenser will dis-charge itself through D R ; and as the resistance of D E isinfinitesimal in comparison with the resistance in any othercircuit, the discharge of the condenser will not send an appre-ciable amount of electricity through the galvanometer. Thus,if we make the moving piece P oscillate quickly from R to S,there will, owing to the flow of electricity to the condenser, bea succession of momentary currents through the resistances are so adjusted that the deflection of the gal-vanometer produced by these momentary currents is balanced * Comrmmicatecl by the Physical Society. Read June 28, On Measuring the Electrical Capacity of a Condenser. 99 by the deflection due to the steady current, and the resultantdeflection is zero. When this is the case, there is a relationbetween the capacity of the condenser, the number of timesthe condenser is charged and discharged in a second, and theresistances in the various arms of the bridge. The investigation given by Maxwell is only approximate ;we shall quote therefore the result given in Thomsons paper. Let a be the resistance of A C,b „ „ AB, c „ „ AD, d „ „ BC, 9 » » DC- Let C be the capacity of the condenser, n the number of timesit is charged and discharged per second ; then a{ l~ (a±c + g)(a + b + d) \ nC = ^^JttA^ ag } >(a + b-\-d)) l d(a + c+g) The commutator was the one used by J. J. Thomson, andwe will quote his description :—lk The current from someGrove cells passes first through a tuning-fork interrupter andthen through
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