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 only akin to those which had been already overcome. More comets no doubt could be found, more minor planets were being constantly discovered, but the older methods did not supply much fresh intellectual pabulum. They provided, it is true, additional material for the application of well-known formulae; they required the computation of tables similar in scope to scores of other tables that were already in hand. But it certainly seemed that if astronomy was to sustain the high interest that it had always possessed, some new departure was necessary in order that the science might exhibit that growth which seems to be an essential requisite of vitality. It was about thirty years ago that the much needed advance was made which opened up to research a vast department of science of a totally unexpected character.

Comte was one of those who, in alluding to the probable exhaustion of attainable astronomical science, indicated some problems which were apparently beyond the reach of our powers. We might, he surmised, find out much with regard to the movements of the heavenly bodies, we might survey their distances, measure their dimensions, and appraise their weight; but, said Comte, to find out their material composition or to learn the actual chemical elements of which they are composed, this problem, though it would be pregnant with interest for us, we could not but despair of solving. It was not many years before this rash assertion was disproved by the splendid discoveries which, to the astonishment of the world, explained the meaning of the dark lines in the solar spectrum, and demonstrated the existence of iron and other well-known metals in our great luminary.

It is essential to the right understanding of the subject to