observation. In the nebulæ we are brought face to face with a substance (or substances) which, as far as our observations go, exists nowhere else except in the very hottest region of the sun that we can get at with our instruments. It is unknown here, and all attempts to match the spectrum by exposing terrestrial substances to the highest temperatures available in our laboratories have so far been unavailing. Both in sun and nebulæ this substance (or substances) is associated with hydrogen. This curdling process will go on until at length further condensation will take place, and instead of having simply the substance (or substances) to which I have referred, and hydrogen, we shall have an excess of hydrogen with an infinitely fine dust interspersed in it, which will go on condensing and condensing until at last we get dust of substances the existence of which is revealed to us in the spectra of bodies known to terrestrial chemistry; among these are magnesium, carbon, oxygen, iron, silicon, and sulphur.
This dust, fortunately for those interested in such inquiries as this, comes down to us in more condensed forms still, and it is in consequence of the messages which they bring from the heavens that I am engaged in writing this article. Not only have we dust falling, but large masses; magnificent specimens of meteorites which have fallen from the heavens at different times, some of them weighing tons, are open to our inquiries. Although, therefore, it is very difficult for us to collect the dust, it is perfectly easy to produce it by pulverizing any specimens of these meteorites that we choose into the finest powder. If we examine this dust spectroscopically, we find that, in addition to hydrogen, its chief constituents are magnesium, iron, carbon, silicon, oxygen, and sulphur.
I have, therefore, in this first sketch of a possible result of a process going on in our space-clearing at an early stage, not arrived at something that is unreal and merely the creation of the imagination, but something very definite indeed, which we can analyze and work with in our laboratories.
How it comes that this infinitely fine dust, finer probably than anything we can imagine, becomes at last, in the celestial spaces, agglomerated into meteoric irons and stones with which the earth is being continually bombarded, is one of the most interesting questions in the domain of science. Space is no niggard of this dust, for if we deal with agglomerations of it sufficient in quantity to give rise to the appearance of a "falling star" to the unaided eye, we know that the number of such masses which fall upon the earth every day exceeds twenty millions.
We have, then, the idea before us that, here and there in-this space that we have cleared, we have initial curdling, as I have called it; we need not assume that these curdlings are uniform.