CELESTIAL CHEMISTRY. 381 



thev prove to be great clusters of numerous stars, and their 

 spectra are just like those of the sun and other stars. But 

 there are also true nebulae, which no telescope, however 

 powerful, has been able to resolve into stars, and Sir William 

 Hugg-ins found that these true nebulae yield bright-line- 

 spectra, showing that they consist wholly of luminous gas, set 

 glowing, probably by the heat caused by myriads of meteorites- 

 in constant collision. They do not yet, like the sun and stars, 

 comprise a molten nucleus surrounded by an atmosphere; so 

 we mav describe them as infant systems. The great nebula in 

 Orion is such an accumulation of glowing gas. In the cases of 

 certain nebulae only incandescent hydrogen and nitrogen have 

 thus been found, accompanied by an unknown element to which 

 the name nebulium has been assigned. 



One of the most remarkable celestial obiects is the great 

 nebula in Andromeda, a stupendous spiral of apparently 

 nebulous matter, which we, from our position in the heavens, 

 see nearly edgewise. Herschel considered it so distant that its 

 light must take nearly 17,000 years to reach us. Professor 

 Bohlin, on the other hand, considers it to be only 19 light-years 

 distant. Even the latter basis would involve the nebula's 

 occupying" more than 20,000 million million times the bulk of 

 our sun, so that it has been suggested by some that this nebula 

 is — not another solar system — but what we may call another 

 universe. It seems moreover to be not nebulous matter alone, 

 for its spectrum, like that of sun and stars, is continuous, and 

 so the inference has been drawn that it comprises many myriads 

 of stars at incomprehensible distances from our universe. 



I must not leave the subject of the nebulae without 

 mentioning that group of stars known as the Pleiades, many of 

 the members of which are surrounded with nebulous matter, 

 and are possibly several solar systems in course of formation. 

 Nor should I entirely omit the Milky Way, which can for 

 the most part be resolved into star clusters innumerable. If 

 we could remove ourselves far beyond the confines of the 

 Milky Way, it is not improbable that the latter would present 

 the appearance of a vast spiral nebula, included in which would 

 be nearly all the isolated stars now visible, and amongst them 

 our own sun. 



I must close. There is much else about which one could have 

 spoken in dealing with the silvern embroideries of the heavens, 

 but time fails. W'e have just lightly touched on the chemistry 

 of the cosmos : beginning with the central luminary of our 

 own solar system, we have glanced at his attendant planets, 

 not omitting our own satellite, the moon, a waterless, airless 

 globe. We have noticed how some of our sister planets shine 

 by the sun's reflected light and others by light of their own : 

 we have attempted to understand the mysteries of the comets 

 that were such objects of dread in former days : then, leaving" 

 our own solar system we have gone further afield to other 

 suns than ours, and yet further, to the possibilities of universes 

 beyond, and we have wondered where all this is tending. The 

 cvcles go on : there is evolution — I scarcely like to use a word 

 that is often and eg-reg'iously misapplied — and there is also 



