Relay, [25], [39], [49], [53], [55], [60], [75]

differential, [79]

polarised, [97]

working speed of, [26], [75]

Reproducing for newspapers, [60]

Resistance of selenium, [109]

of selenium cells, [110]

regulating, [113]

Retardation of current, [6]

Retouching, [62]