Prototype of Mudford's improved form of Kelvin's astatic galvanometer
Prototype of Mudford's improved form of Kelvin's astatic galvanometer
Prototype of Mudford's improved form of Kelvin's astatic galvanometer, with letter from Kelvin approving Mudford's improvement
Prototype of Mudford's improved form of Kelvin's astatic galvanometer
Letter from Kelvin approving Mudford's improved form of Kelvin's astatic galvanometer