68 THE POPULAR SCIENCE MONTHLY. 



observation. In the nebulse 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 labora- 

 tories have so far been unavailing. Both in sun and nebulse this 

 substance (or substances) is associated with hydrogen. This curd- 

 ling process will go on until at length further condensation will 

 take place, and instead of having simply the substance (or sub- 

 stances) 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, there- 

 fore, it is very difficult for us to collect the dust, it is perfectly 

 easy to produce it by pulverizing any specimens of these meteor- 

 ites 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 ar- 

 rived 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 ques- 

 tions 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. 



