Hall's Experiment

A cro of thin metal, such as gold leaf, is secured upon a pane of gla . To two opposite arms a battery is connected in circuit with them. To the other two arms a galvanometer is connected in circuit. If the cro is put into a field of force whose lines are perpendicular thereto, the galvanometer will disclose a constant current. The current is pushed, as it were, into the galvanometer circuit. Other metals have been used with similar results. They must be thin or the experiment fails. If the arm receiving the battery current is horizontal, and if it flows from left to right, and if the lines of force go from downward through the cro , the current in the galvanometer circuit will flow from the observer through the other arms of the cro , if the cro is of gold, silver, platinum or tin, and the reverse if of iron. The experiment has indicated a po ible way of reaching the velocity of electricity in absolute measure.