ABSTRACT
Manifestations of electricity seem to be associated with almost every kind of activity in the universe. In the non-living world, such things as friction, the evaporation of water, the transference of heat, the passage of liquids through membranes, chemical activity and magnetism are all accompanied by the production of electricity. The mirror galvanometer was invented by Lord Kelvin to indicate the presence of electric currents in submarine cables, but it has been found well adapted to display currents of animal electricity. In this instrument a spot of light reflected from the mirror moves to the right hand or to the left on a white wall every time a current passes round the galvanometer. The latest development in the study of animal electricity is to photograph the currents of the beating human heart. This is done to-day by means of a very delicate and costly apparatus called the “string” galvanometer, because in it a fine filament oscillates.
