MAGICAL SCALES.

Lake Wakatip Mail, Issue 2904, 31 January 1911, Page 7

MAGICAL SCALES.

WEIGHING A SEVEN-THOUSAND-MILLIONTH OF AN OUNCE. To a small underground chamber below his own laboratory at University College, London, Sir William Ramsay, the famous scientist, recently led a visitor. "I will show you," he said, "a pair of scales which will weigh a seven - thousand - millionth of an ounce." The room was in semi-darkness. So delicate are thlse wonderful scales that their balance is disturbed by the alteration of temperature caused by the turning on of an electric light at the other end of the room. The operator has to leave them for an hour in darkness—after he has tip-toed from the room so that hia footfall should not set up any vibration—and then read them swiftly before any change in the temperature has had time to affect them.

The, scales rest in a metal chamber. The beam, only a few inches long, appears a mere cobweb of*glass with its frail supports. It is not mad 3(f glass, however, explains Sir William, but of silica, which expands and contracts under the effect of heat far less than glass.

Hanging from one end of the beam of the scales by a strand of silica fibre so slender that it is scarcely possible to sec it is a 'stay. Upon this is placed a minute glass tube. Imprisoned in the tube is a whiff of Xenon, a gas discovered by Sir William Ramsay. The movement of the scales when the tube is dropped upon them is so slight that it cannot be detected at all by the eye. But the movement is made to swing from side to side a tiny mirror, upon which a beam of light is focused. The result is that a shifting point of light is thrown upon a graduated black scale six feet away. The weight of the tube, with the gas in it, is then recorded by the movement of this pin-point of light on the scale.

Then comes the interesting test. The gas is released from the tube, which is weighed again. It is now found to weigh a two-hundred-and-fifty-thousandth •of a milligramme, or a seven-thousand-millionth of an ounce, less than it did when the gas was in it. Therefore the weight of this whiff of gas was a seven-thou-sand-millionth of an ounce. The smallest object that can be picked up with the most delicate forceps is a piece of aluminium wire far thinner than a human hair, a 25th of an inch in length, which weighs a fourteen-hundred-thousandth of an ounce. It can scarcely be seen, and it is difficult to detect whether it is resting on the scales or not. A section of aluminium wire weighing an eighty-four-hundred-thousandth of an ounce can be prepared. But it is only visible in a microscope. For this reason weights of less than a fourteen-hundred-thousandth of an ounce have to be registered in gases, -"Tit-Bits."