so that we shall have no huge useless inert mass existing in after ages to remind the passer-by of a form of energy and a species of matter that is long since out of date and functionally effete. Why should not the universe bury its dead out of sight?

CHAPTER V.

DEVELOPMENT.

"Are God and Nature then at strife,
That Nature lends such evil dreams?
So careful of the type she seems,
So careless of the single life;

"So careful of the type'? but no,

From scarped cliff and quarried stone
She cries, A thousand types are gone :
I care for nothing, all shall go.""-TENNYSON.

"All nature is but art, unknown to thee;

All chance, direction, which thou canst not see,

All discord, harmony not understood;

All partial evil, universal good;

And spite of pride, in erring reason's spite,

One truth is clear, whatever is, is right.”—POPE.

154. IN Chapters III. and IV. we have dwelt upon the laws of energy and the ultimate constitution of matter; in other words, we have discussed those laws according to which the machine called the visible universe works, as well as the probable nature of that material of which it is composed. We have in this process (Arts. 86, 151) come to the conclusion that the visible universe has been developed out of the invisible. Once developed, it has its own laws of action which we may discover,-laws which at present appear to be invariably followed, as far at least as our strictly scientific experience can inform us.

In fine, the visible universe is that which we are in a

position to observe, gaining an insight into its present method of working, and trying also to reply to that very interesting question, Has it always worked in its present manner, or has there ever been any apparent break?

Let us, therefore, take this visible universe after its production, and endeavour to become acquainted with the course of its development. What did it do? Was it entirely left to itself, and to what may be termed the natural laws impressed upon it when it was produced?

In replying to these questions, let us, for the sake of convenience, consider development under the three following heads, viz., (a) Chemical or Stuff Development, (6) Globe Development, (y) Life Development.

155. To begin with chemical or stuff development, we come at once to a very interesting and important question. Assuming that the atoms of the present universe were developed from the invisible, were different kinds of atoms thus developed, or were they all of one kind?

To this question the chemist of last century would have replied :—Undoubtedly there were many kinds of primeval atoms, and then would follow a list of all these various substances which he was unable to decompose.

The chemist of thirty or forty years later would still reply to the question in the same way, but he would probably have a different list of primeval elements less formidable in number.

If the chemist of forty years ago were asked, he would have furnished a list of perhaps fifty simple substances; but then, probably, the minimum would have been reached; for ask the chemist of to-day, and he will furnish a list of sixty-three elements.

156. But while the number of undecomposed bodies is

slowly increasing, chemists are beginning to speculate as to the possibility of these so-called elements being in reality nothing else than combinations of some kind of primordial

atoms.

This idea was first entertained by Dr. Prout, the wellknown physician and chemist. He pointed out that the atomic weights of the various so-called elements are very nearly all multiples of that of the half of hydrogen, so that they may possibly be looked upon as formed by a grouping together of certain atoms of half the mass of the hydrogen

atom.

M. Stas, the distinguished Belgian chemist, instituted a laborious series of experiments with the view of testing this doctrine. He came to the conclusion that the atomic weights of the various elements were not precisely multiples of that of the half of hydrogen, there being greater differences than could possibly be accounted for by errors of experiment. His researches, however, seemed to show that in many cases there was a very near approach to Prout's imagined law. But in no case does the discrepance appear greatly to exceed what may easily be attributed to unavoidable impurities in the substances operated on; say only those due to the condensation of gases in the pores of solids, which (in certain cases at least) is known to amount to a very considerable quantity.

157. From another point of view, there appears to be evidence in favour of the so-called elementary bodies being built up.

There are certain groups or families amongst these elements of such a nature that the various members of one family appear to be related to each other, in the same way as the corresponding members of another family.

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 in the way of 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 resisted all attempts at decomposition, and there are other similar instances that might be named.

158. It has, however, at the same time, come to be recognised, that 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 or H2O from one another in the case of steam. It is now understood that high temperature has also the power of separating the atomic constituents of a single molecule from each other, so that at an extremely high temperature water would not only 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; thus we see that carbonate of lime is 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 some