TAKING THE TEMPERATURE OF A STAR.

Hokitika Guardian, 3 May 1924, Page 4

TAKING THE TEMPERATURE OF A STAR.

(.). A. Lloyd in Daily Mail)

To measure the boat we get front a star seems a hopeless job. Vet it can be clone.

Naturally, the measurement is almost inconceivably delicate. The instrument employed, tailed a ••radiation pyrometer,” is a triumph of refined mechanical work. It is so exquisitely frail that, compared with it, a woman's wrist-watch would look like a colliery winding-engine. Electric]’tly does the measuring. Essentially, the instrument consists t.i' a tine thermo-couple formed by the union o| two wires, cue of platinum, ilie other of silver. At the junction of ibe wires is placed an absorbing surface about as large as a pin’s head. This is painted black, ami the light of the star to he teted is focused on this surface. The wires arc so fine that they are quite invisible to the unaided eye. When the rays of the star are focused on the thermo-couple an electric current Hows along the wires. The strength of the current gives a measure of the star’s heat-radiation. Tlie galvanometer by which the cur l rent is measured coii-ists ol ail exceedingly small mirror less than a pin's head in size, hung from a thread of spun quartz, which i- the finest thread known. A mark on the face of the mirror throws a reflection on an illuminated scale which is read b.v a

The pyrometer, in actual u-e. is enclosed in a gla-s cell from which all the air has been exhausted. In the glass cell there is a window of iluorile through which the light of the slai falls on the thermo-couple. The whole instrument is now placed in the focus of a reflet-ting telescope of three feet aperlure, and the light of the star adjusted to fail on tin fluorite window. If the star gives out any appreciable heat, the current of electricity sef up in the thermo-couple causes the quartz, thread in the .galvanometer to twist, and the rcileciion of the little miii'or oscillates to and tro on the scale.

The instrument is so extraordinarily sensitive that it call measure to the millionth of a degree!

The heat of a single candle can he f.-ll by this marvellous colli rivanee at a distance of fifty-three miles.