A new thermionic instrument

N. E. Bonn: Mr. Hoare´s instrument will undoubtedly be found very useful for certain special applications. For general laboratory work and as a detector in ordinary bridge and potentiometer circuits its value is very much limited by the exceptionally high internal impedance. True, it can be made to give a full-scale deflection while drawing only 0.1 microampere from the circuit, but it takes fully 0.3 volt to do so, and such high voltage is not available when one measures temperatures by means of thermocouples or in ordinary Wheatstone bridge and potentiometer circuits.