WHAT IS THE SUN MADE OF ? 455 



planet, or whether of materials identical in nature with some 

 of those of which the earth is composed, was beyond the scope 

 of human ken, and seemed likely to remain so. The lighter 

 weight of the sun conveyed no information as to the nature 

 of the materials. The proportional weight of the same thing 

 varies according to the amount of heat it has. For example, 

 metals the very heaviest class of bodies can by the aid of 

 sufficient heat be driven into vapour ; and vapours, as we all 

 know, are characterised by their lightness. So, it might be 

 that the sun was composed of materials naturally heavy, but 

 expanded to lightness by heat ; or it again might be that the 

 sun was composed of materials naturally light light, that is 

 to say, at ordinary temperatures. 



Long ago, the opinion began to prevail that the sun w r as 

 a molten mass of fire ; and a very rational opinion to most 

 people this will seem to be, considering the heat and light 

 ever evolved from the great centre of our system. Then 

 afterwards came a period when that opinion fell pretty much 

 into the back-ground amongst philosophers. It was argued 

 that both heat arid light might be produced by an orb neither 

 inordinately hot nor luminous ; an opinion that could never 

 have gained much acquiescence by the unlearned much 

 philosophical refinement of thought being needed to reconcile 

 the mind to the notion of heat and light being produced by a 

 body of itself neither hot nor luminous. 



Such continued long to be the sum-total of our knowledge 

 in regard to the sun's composition. Doubting, speculating, 

 we lived, but never hoping. Philosophers little knew what a 

 glorious discovery was in store for them. 



Everybody knows what is meant by the term e prismatic 

 spectrum,' the wondrous coloured image thrown upon a screen 

 when a jet or thread of white light is analysed, or unravelled, 

 so to speak, by means of a transparent triangular prism. 

 Whatever the source of light may be, provided it evolve 

 white light, a coloured spectrum may be produced by the 



