THE HEAT OF A STAR.

Mataura Ensign, 20 March 1909, Page 3

THE HEAT OF A STAR.

A MARVELLOUS MACHINE The nearest, star lo the earth is Alpha Coiitiiuri, the brighter of the J houlhel'li pointers, and it is so far away from us that its light lakes lour years] to reach us. It looks a mere |x.mt of light iii the sky. The telescope reveals two |Hiiuts <>l Unlit, because it. i.s a j (loiihlo slat, lint even from the two, (Stars it is inconceivahle that any ht-aLj could reach us across so enormous an interval of space. Vcl some heat docs reach iho narl.li, and although it is so linle that no ordinary I hcrmomcter can ] detect it, man has succccih d in iiijf il. Professor Samuel I*. Langlo.v has made a little instrument, for measuring very delicate variations of icni-, peraiure, using the well-known principle that the resistance offered by a iwi-lal lo the passage of an electric current viries according to the temperalure of the metal. In his experiments for this purpose the star ray was caught upon a large mirror disc and relleeled upon the centre ,if another mirror of concave shape. The second mirror in its turn, concentrating the ray, threw it upon a thread of platinum almul the thickness nf the filament a spider spins. Through this thread a current, of electricity was Kept continually flowing. In order to determine the temperature of the plati. mini thread it was merely necessary to measure its electrical resistance, 'and this ivas accomplished by the aid of an extraordinarily sensitive galvanometer. The electric current pa-sing through the phii ilium thread heid ihe heam of the galvanometer in place. Whan the enricnt varied the h,am moved. This beam consisted of a thread of spun glass five inches long and as thick as a human hair. In its centre was !i\ed a finv glass mirror weighing about a-, much as Ino leg of a lly. The beam was suspended In,in a fibre of spun uuartz two feet long and one fivo-th n .:,:idth of an inch thick. A ray of li'.jn i,,,,,. a candle I'll uwu the litth> mirror, which in turn Ihrew a dot of li-ht, on a measuri:e: -ale. The rav from t1,,. star was a lowed t„ lall on the ciaiinuuiHhread, the resistance of I lie tin. a I lo the electric current n, hiciviim,!. ilie beam of Hie galvanometer moved, and as it moved thedotof li K l,t I ravelled up the fccalc and the heat received from the star had been measured.