CHAPTER XXXV.

Electrolytic Registering Meter.

An ingenious form of electrolytic meter attributable to Mr.Tesla is one in which a conductor is immersed in a solution, soarranged that metal may be deposited from the solution or takenaway in such a manner that the electrical resistance of the con-ductor is varied in a definite proportion to the strength of thecurrent the energy of which is to be computed, whereby thisvariation in resistance serves as a measure of the energy and alsomay actuate registering mechanism, whenever the resistancerises above or falls below certain limits.

In carrying out this idea Mr. Tesla employs an electroly-tic cell, through which extend two conductors parallel andin close proximity to each other. These conductors he connectsin series through a resistance, but in such manner that there isan equal difference of potential between them throughout theirentire extent. The free ends or terminals of the conductors areconnected either in series in the circuit supplying the current tothe lamps or other devices, or in parallel to a resistance in thecircuit and in series with the current consuming devices. Undersuch circumstances a current passing through the conductorsestablishes a difference of potential between them which is pro-portional to the strength of the current, in consequence of whichthere is a leakage of current from one conductor to the otheracross the solution. The strength of this leakage current is pro-portional to the difference of potential, and, therefore, in propor-tion to the strength of the current passing through the conductors.Moreover, as there is a constant difference of potential betweenthe two conductors throughout the entire extent that is exposedto the solution, the current density through such solution is thesame at all corresponding points, and hence the deposit is uni-form along the whole of one of the conductors, while the metalis taken away uniformly from the other. The resistance of oneconductor is by this means diminished, while that of the other is