CELESTIAL CHEMISTRY. 379 



Bull's eye, as it is sometimes called, situated in the constellation 

 Taurus, about midway between Orion's head and the Pleiades, 

 was found by Hugg'ins and Miller to contain, in addition to 

 some of the elements fotmd in our sun. also bismuth, tellurium, 

 antimony and mercury. Betelgeuse again, the brightest star in 

 the constellation Orion, apparently a cooler sun than ours, con- 

 tains no hydrogen at all, although magnesium, calcium and 

 sodium are present in its atmosphere. In the case of Sirius, on 

 the other hand, that brightest of all the fixed stars, the hydrogen 

 lines are very much intensified, while the lines produced by the 

 metals are very faint. Some of the hotter stars, like Rigel, 

 Bellatrix, and three others in (Jrion, have recently been found 

 to contain sulphur. 



Some stars are almost inconceivably hotter than others, and 

 the spectroscope enables tis to take their temperature, so to 

 speak. If we take a cold iron poker out of the fender, and 

 look at it through the spectroscope, we see no spectrum what- 

 ever — nothing but absolute blackness. But if we put the end 

 of the poker amongst the blazing coals on the hearth, and 

 take it out at intervals in order to examine it through the 

 spectroscope, we find that when the poker gets to a dull red 

 heat a spectrum begins to appear; not, as one may imagine, a 

 spectrum showing all the colours from red to violet, but show- 

 ing" them faintly; no, only the red portion of the spectrum 

 shows; nothing more. As the poker gets hotter the spectrum 

 gradually lengthens out — to the red is first added orange then, 

 as the temperature rises, the yellow begins to appccir, next 

 comes green, then blue is joined on, and finally violet. The 

 poker is by this time white-hot. A white heat obviously im- 

 plies that all the colours of the spectrum are present. But we 

 can heat the poker even beyond this, and the spectrum goes on 

 lengthening out beyond the violet into regions where the human 

 eye can no longer follow it, but where the photographic 

 camera is still able to take cognisance of its gradual extension. 



Now we can understand how the temperature of the stars can 

 be taken. There are stars wath short red spectra — these are the 

 cooler stars. There are others with spectra extending deep 

 into the ultra-violet regions — these are the hottest stars of 

 which we know, having an estimated temperature of 30,000 

 degrees Centigrade. • 



just at this point we enter upon a subject so stupendous that 

 it is wholly impossible to do more than merely touch the ex- 

 treme fringe, but let me just give the salient facts. I have de- 

 scribed the different kinds of spectra, showing how we could 

 distinguish a glowing solid from an incandescent metallic vapour. 

 Now it has been found by the spectroscope that the cooler stars 

 give evidence of the presence of red hot carbon chiefly; those 

 of medium temperature are the stars which, like our own sun, 

 consist pf molten and vaporous metals; and the hottest stars are 

 simply incandescent gases. 



Sir William Ramsay has found that the metal radium breaks 

 up and forms helium. He also claimed to have dissociated cop- 

 per and got lithium from it. This last claim has been disputed, 

 but it is practically certain that the great heat of some of the 



