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Page:Popular Science Monthly Volume 38.djvu/81

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Smash, a meteorite, collect the dust, expose it to a low temperature; compare its spectrum with the spectrum of such, a body as those we have been considering, and see by actual experiment if there is any similarity. This was done.

The result was almost identical. It seemed, therefore, that one had at last got to solid ground, and could go ahead. But how to go ahead in a scientific way? Naturally by developing the argument which had led us so far. Let us agree that the nebulæ are condensations of meteoritic dust, and see whether we are led to the true or the false by such a concession. Let us further grant that the condensations go on. What will happen next?

In certain regions of space the encounters—the collisions—will increase in number in consequence of the accumulation of meteoric dust in these regions; the temperature will, therefore, be higher and the light more intense.

Is there only one process by which, the temperature can be increased? It did not take very long to recognize that there might possibly be three lines of action, each one of which would result in the production of a higher temperature. In the first place, moment of momentum—rotation—being at our disposal to start with, it was obvious, in virtue of mechanical laws, that as the condensation went on the rotation would be accelerated; the motions of the particles of dust in the reaction, so to speak, would be more violent; the collisions, therefore, would produce more smashes, and more heat, and therefore more light.

We should get a central system and surroundings, such as Mr. Roberts has recently photographed in the great nebula of Andromeda. The exposure he gave was four hours, and again this photograph brings us face to face with phenomena which will probably never be seen by the eye alone.

A central condensation, here and there fragments of spirals, and here and there dark gaps, are seen. These gaps were observed by Bond and others years ago, but it remained for Mr. Roberts to demonstrate to us that they are produced by the wonderful indraught action which we can now, by means of the photograph, see going on. We have a concentration toward the center, the dark gaps representing to us either the absence of matter or the presence of meteoritic dust in a region where it is all going the same way, and in which, therefore, there are no collisions. Here and there we get regions of great luminosity, and associated with the spirals we get obvious loci of encounters. External swarms are also seen which have been thought, with great probability, to belong to the system—smaller condensations partaking in the general motion of the whole. Here, then, we are in presence of one possible cause of increased temperature.

There is another. One of the early results obtained by Sir