Rotation of the Earth

Manawatu Times, Volume LVI, Issue 6519, 7 April 1931, Page 5

Rotation of the Earth

SCIENTIST’S EXPERIMENTS. An experiment to prove by means of a pendulum that the earth rotates on its axis was successfully repeated by the Argentine Astronomical Society at Buenos Aires recently. The society employed the method used by Jean Foucault when he performed the same experiment for the first time eighty years ago, and the same results were obtained. As long ago as 305 B.C. Hcraclidcs of Pontus taught that the earth turned on its axis. But it was generally thought, even through the Middle Ages, that the earth was stationary, and that the heavens revolved round it. Though the revolutionary work of Copernicus in the sixteenth century and the observations made possible by the invention of the telescope made this belief in an unmoving earth improbable, it was not until ISSI that Foucault was able to show that the earth actually rotates on its axis. His conclusion has since been verified by other experi mental methods. From the dome of the Pantheon at Paris Foucault suspended a heavy iron ball by a wire about 200 ft. long. A pin attached to the bottom of the ball touched a layer of sand spread on a table below. Thus the movement of the pendulum was traced by the pin on the layer of sand. Having arranged these matters to his satisfaction, Foucalt held the pendulum stationary by means of a cotton cord for several hours or until the pendulum had become absolutely still. Then the cotton cord was burned in order to start the hall swinging without any jar. It was observed that, with each vibration, the pin cut the sand at a different place, instead of drawing only one line, as would have happened if the earth were not rotating. The pin shifted to the right at such a rate that a complete rotation would have boon made in 32 hours if the pendulum had not come to rest.

At the North Pole such a complete circle would take 24 hours, equivalent to an ordinary day. At the South Polo the period would be the same, but the direction would be toward the left instead of the right ,while at the equator there will be no such tendency to shift. From these facts the following explanation of the Foucault experiment has been made by Russell, Dugan and Stewart in their manual on astronomy. “The northern edge of. the floor of a room in the northern hemisphere Is nearer the axis of the earth than is its southern edge, and therefore is carried more slowly eastward by the earth rotation.' Hence the floor must skew round continually, like a postage stamp gummed upon a whirling globe. The pendulum is constrained by the force of gravity to follow the changes in the direction of the vertical, but is otherwise free.”

The success of Foucault’s experiment and his invention of the gyroscope in 1852 led to his receiving the Copley medal of the Royal Society in 1855.