The unseen universe

by Balfour Stewart; Peter Guthrie Tait

This clearly points to some sort of community of origin, and thus favours the idea that the elements are in reality composite structures. But the great difficulty felt by those who have favoured this idea has been the apparent impossibility of decomposing such family groups. Thus fluorine, chlorine, bromine, and iodine, while they appear to be related to one another in some peculiar manner, have yet apparently resisted all attempts at decomposition, and there are other similar instances which might easily be named.

158. It has, however, at the same time, come to be recognised, that heat of high temperature is a very powerful decomposing agent, and that its office is by no means limited to causing the separation from one another of the molecules of a substance, as, for instance, when it separates the molecules of water-substance or H₂O from one another, as in forming water from ice, or steam from water. It is now understood that high-temperature heat has also the power of separating the atomic constituents of a single molecule from each other, so that at an extremely high temperature not only would water be driven into steam, but steam driven into oxygen and hydrogen. We are already familiar with many instances of this power possessed by high-temperature heat; thus we see carbonate of lime decomposed by the heat of the kiln into lime and carbonic-acid gas. We see also that at the high temperatures which accompany the electric spark almost all compounds are momentarily decomposed, if we may judge by the spectrum of the light which is given out. Carrying on this line of thought, we are led to imagine that, could we obtain higher temperatures than those now at our disposal, we might decompose some of those substances which at present seem to be elements.

159. Lockyer, in his astronomical researches, has recently started this question. He argues that in the sun and stars, and more especially in the whiter stars, there are temperatures very much higher than any which have been here produced. He assumes too that simplicity of constitution accompanies a simple spectrum, an hypothesis which is consistent with the fact that compounds as a rule give spectra much more complicated than those of simple substances. Now it is a curious circumstance that the atmospheres of some of the whiter stars, such as Sirius, do not appear to contain anything but hydrogen; at least we have no indication that they do; other stars, again, of less whiteness, in addition to hydrogen, have such substances as iron, sodium, etc., while yellow, orange, and blood-red stars and variable stars, appear to contain in their atmospheres substances which are compounds. If then it be true that as a rule the atmospheres of the whiter stars contain the fewer elements and those of smallest atomic weight, and that as stars diminish in whiteness their atmospheres rise in complexity of structure, in fine, if we have reason to associate together whiteness and simplicity, this undoubtedly tells in favour of the power of high-temperature heat to split up the so-called elements.

We conclude the whiter stars to be the hotter stars, from the fact that their spectra contain a greater proportion of the more refrangible rays than do those of yellow or red stars.

In fine, a speculation of this nature is not to be summarily dismissed, but ought to be retained as a working hypothesis which may in time throw great light on the ultimate constitution of the chemical elements. Is it fanciful to suppose that the passage prefixed to [Chapter III]. may refer to this, since (literally translated) it stands—‘... the elements, intensely heated, shall be broken up....’?

160. Let us now turn to globe development. We have alluded to this already while discussing the energy of the universe. In doing so we came to the conclusion that the original state of the visible universe was a diffused or chaotic state, in which the various particles were widely separated from one another, but exerting on one another gravitating force, and therefore possessed of potential energy. As these particles came together, impinged on one another, or gathered into groups, this potential energy was gradually transformed into the energy of heat and into that of visible motion. We may thus imagine the cooling and (except under very strict conditions of original distribution) necessarily revolving matter in course of time to have thrown off certain parts of itself which would thereafter form satellites or planetary attendants, while the central mass would form the sun. We have here, in fact, the development hypothesis of Kant and Laplace, and it is greatly in favour of the truth of this hypothesis that all the planetary motions of the solar system are nearly in one plane, and also that, looking down on the system from above that plane, all these motions are seen to be in one and the same direction.

161. Assuming, therefore, that the solar system and, pari passu, the other sidereal systems have been formed in this way, it is very easy to see why the central mass should be so much hotter than its attendants. Two causes would conduce to this. In the first place, assuming that the heat of a mass is due to the rushing together of its particles under the force of gravitation, the velocities would be much greater for the central mass, and hence the amount of heat (per unit of mass, i.e. the temperature) developed would be greater also. In the next place, the body being a large one would cool less rapidly than its attendant planets. These two causes thus combine to render the largest bodies of the universe ever since their aggregation (and still more now) the hottest, so that the same body which forms the gravitating centre of the system becomes, when required, also the dispenser of light and heat.

162. Now, without speculating about the nature or extent of the ethereal medium, we may be sure of two things. In the first place, all but an exceedingly small fraction of the light and heat of the sun and stars goes out into space and does not return to them again, or in other words, the sun and stars are slowly cooling. To restore to the sun every instant its losses by radiation, the whole celestial vault would have to radiate as powerfully as the sun does—in which case the earth and planets would very soon acquire (at their surfaces) the sun’s temperature. In the next place, the visible motion of the large bodies of the universe is gradually being stopped by something which may be denominated ethereal friction. It follows from this that our own sun will gradually lose his brilliancy, and that our earth will gradually lose its orbital energy and approach the sun in a path of slowly contracting spiral convolutions. At last it will become entangled with the sun, and the result will be the conversion of the remaining orbital energy into heat, after which the two bodies will remain one.

Thus the tendency is that the sun shall ultimately absorb the various planets of the system, his heat and energy being recruited by the process. Now, let us imagine that the same processes are simultaneously going on in one of the nearer fixed stars, say for instance in Sirius.

After unimaginable ages these two stars, the Sun and Sirius, having each long since swallowed up his attendants, but being nevertheless exhausted in heat-energy on account of radiation into space, may be imagined to be travelling towards one another, slowly at first, but afterwards with an accelerated motion.