So much, then, for the present regard ing our own earth. We have now to consider the various bodies external to our planet; to take, for purposes of comparison, a hasty survey of the host of heaven, or rather to dwell on typical specimens, so to speak, carefully selected from among them.

Here of course our methods of inquiry are totally different. Here experiment is impossible. The crucible, the balance fail us; we are driven from experiment to observation.

But still it is experiment which permits the observer to read the riddle presented to him, the moment we leave the telescope and employ that instrument by the aid of which above all others our recent knowledge has been obtained-I refer to the spectroscope.

Indeed, it is not too much to say that without the information which the spectroscope has enabled us to harvest concerning the various orders of celestial bodies, the Earth's Place in Nature must for ever have remained like a land of dreams and fancies, of hopes never to be realised, of theories never to be brought to the test. The history of our planet would have been a fragment, its future a ground untrodden by the scientific inquirer. The new impulse to study the little ball on which our lives are lived, and the firm vantage ground which we now possess, have arisen from the fact that, while not many years ago the matter and the condition of matter exterior to our earth were but guesswork, we are now as familiar with the chemistry of distant worlds as we are with the chemistry of our own a few miles below the surface. We know that the elements we are familiar with here are represented there.

In fact, we know that the whole cosmos, so far as science has anything to say to the vast problem which it sets before us, consists of matter, common in its nature, floating in a vast ocean of ether, that is, of a medium finer, so to speak, in its texture than matter, and certainly differing from the most attenuated matter that we know of. And the visibility of the cosmos, and the possibility of the sciences of experiment and obserNEW SEKIES.-VOL. XXVIII., No I

earth and of the bodies exterior to it has been accumulated, depends upon this: the function of matter in all its forms is to vibrate, and the function of the ether is to pulsate with these vibrations, communicating them to us in the process.

Now I have not written this merely because it is the root of the whole matter, as it is, but because we can now, in these later days, pick out these vibrations coming to us from every star, and by studying them find out the kind of matter that has given them birth.

This is a statement so important that I feel I must prove it before I go further, even at the risk of appearing to wander somewhat from my subject.

Before I have finished I am sure it will be conceded that although I have to deal with the largest masses in creation, I was quite right to begin with the smallest.

These smallest particles of matter, with the motions of which modern science enables us to become familiar, are termed molecules, and it is due to the motions of these, as I have said, and not to the motions of large masses, that we have any contact with the world external, not only to our planet, but to each of us individually, so far at all events as the eye is concerned.

The work then to which I have now to call your attention is based primarily upon the motion of molecules. Now, what is a molecule? I have never been to Aberdeen, but I believe there are there enormous quarries of granite, and I know that a great many of the streets of London are paved with granite, and the ultimate fate of this granite is, that it is carted away as road dust-fine road dust. We have no molecules there in the physical sense. We may take the whole ocean and divide it into drops of water, but we have not there molecules in the physical sense. In fact, in both cases we want something very much finersomething approaching, although we won't quarrel about names-to the atoms existing in a drop of water, about which Sir William Thomson has made some calculations. It results from his beautiful and suggestive methods of reasoning that if by any possible means that you could devise, you magnified a drop of water up to the size of the earth, then the finest constituents of that drop of

4

water would then be found to be in sizes varying between fine shot and cricket balls. If you, with your mind's eye, will magnify the drop of water, or the smallest piece of granite dust which you can imagine in that way, and then take the ultimate particles of it, you will then see something like what the physicist regards as a compound molecule for even in the state of fineness to which the water has been brought, each molecule is a chemical compound of oxygen and hydrogen.

Steam furnishes a familiar example of a still coarser molecular state; the steam-engine depends for its action upon the fact that by heat we can drive water into vapor which we call steam. Now, until we get matter into a finer molecular state than is represented by, let us say, the vapor of water in Watt's engine, the vibrations of the molecules tell us little or nothing when we question them by means of the spectroscope about their chemical nature. They only tell us that we have not got matter into its finest state.

But when instead of boiling water, which we can do with a very low temperature no one ever saw water red-hot for this reason-we use a high one and boil something else which will only boil under such conditions, we can produce vapors of excessive fineness of structure. We can thus obtain the vapor of iron or any other metal; and then we find not only that the higher temperature now employed has given us a finer molecular state, but that the phenomena observed are very beautiful, but at the same time somewhat complex.

Why do I say that the phenomena observed are very beautiful but at the same time very complex? Because this high temperature has not only brought about this very fine molecular state with which we are now dealing, but it has caused the molecules thus liberated from their state of durance in the solid or liquid states to shake, quiver, or vibrate after their own manner, and in the intensest fashion after such liberation. The vapor of iron gives us very different impressions from solid iron when it is thus made to glow change the state you change the phenomena.

Not only so, but the same molecules that glow and shiver when they are hot

or even when light falls upon them, are invisible when they are cold and have no light to reflect.

We find, in short, that the visibility of everything depends upon the motions of the molecules of which it is built up. The visibility of a gas, for instance, agitated by an electric current, depends upon the rapid motion of the molecules. We do not see the gas when I do not cause the molecules of which it is composed to enter into rapid motion or vibration, because the light that a gas reflects is not such that the eye can pick up. Such bodies we call transparent. Visibility thus depends upon the motions of molecules. This is a point on which I have strongly to insist. We find further, that when we get matter in such a finely divided condition the visibility not only enables us to see where the molecules are, but what they are. The vibrations of these molecules are independent of temperature, and independent even, I think, of the solid, liquid, or gascous states, provided always that the molecular state is not disturbed.

By using the electric lamp, and exposing calcium, lithium, sodium, &c., to a high temperature, we can get these vibrations, writing their record as spectrum lines upon a screen. These lines are due to the motions or vibrations of the ether producing what we call light, which light is made to pass through a fine slit, afterwards it is sorted out by the refractive power of the prisms. not only know that we are beholding results caused by molecules very rapidly vibrating, but we can tell the calcium from the lithium, or the lithium from the sodium. Now this is spectrum analysis.

We

Further, I may add that these molecules, when they are not vibrating with very great rapidity, are yet prepared to do so if they can get supplied with energy; and they can get this without the direct application of heat if a very brilliant light is made to pass among them. Light which would otherwise pass through is stopped, if the vibrations of the molecules agree with those of the light, or if the molecules can select any vibrations concordant with their own. So that we have not only an opportunity of telling what molecules we are dealing with, when they are rapidly vibrating in con

sequence of being directly heated or electrically excited, but we can tell what they are when they are almost at rest, provided we can observe what kind of light they are competent to absorb.

In the use we can make of the luminosity of bodies, therefore, we are not limited to grasping merely the various facts touching the existence, form, and size of communities of molecules, but the vibrations are so subtle that their chemical and physical constitutions are also more or less revealed to us if we analyze the very light which builds up the form to our eyes, provided always that the individuality of each molecule is allowed to come into play. In a word, by means of the eye we grasp light without analysing it; by means of the spectroscope we can actually perform such analysis.

Recent researches have given rise to the supposition that, when we talk about the vaporous state of matter, represented let us say by steam or the vapor of iron, we are probably talking of at least five different states, which we can distinguish when we use the prism. We have, first, the state that gives us a spectrum consisting of bright lines, to which reference has already been made. Next, we have the spectrum state called the channelled space," or "fluted" spectrum, which represents, in all probability, the second order of complexity of the molecules of any one substance. Contrasting the spectrum of carbon with the spectrum of iron at the highest temperature we usually employ, we gather from this kind of evidence that the molecules of carbon are more complex at that temperature than the molecules of iron.

We can go further with carbon, but with our tiny temperatures we cannot go further with the iron. I need scarcely refer to the other molecular states of vapor to which I have drawn attention, because when we get them, although we can tell that we are dealing with a vapor, we cannot tell which particular vapor is in question. No two substances which give a line spectrum give the same order of lines from one end of the spectrum to the other; in other words the line spectrum of each chemical substance differs from that given by any other. The same thing is true of those which give a channelled space spectrum.

Here then is one of the secrets of the new power of investigation of which the spectroscope has put us in possession : we can recognise each element by its spectrum, whether that spectrum is produced in the laboratory or is given by the most distant star, provided the element exists both here and there.

Let me give an instance of the way in which this knowledge is utilised. Suppose the sun were built up of gas. Suppose the gas hydrogen, we now know that the sun would give us a spectrum of bright lines, the position and arrangement of which are perfectly well known. That question has been put to the sun. The sun does not give us a spectrum of bright lines at all. Supposing the sun were a solid piece of granite, let us say, or of wood, or anything else in which the molecular organisation is extremely complex, as it is in solids and liquids; in that case we should get a continuous spectrum, we should not get lines; but we should get a band of exquisite color, stretching from the red to the violet, as in the rainbow. That experiment has been tried, and the sun does not give us such a spectrum. But there is a third case: suppose the sun to consist of something of which the molecular complexity is very great, and to be surrounded by molecules, not vibrating very rapidly, or, at all events, not vibrating so rapidly as the molecules of the sun itself, what would happen then? It is clear that in that case the external molecules would use the energy which they could extract from the light passing through them from the hot sun, and in that case we should get evidence of the action of molecules in this way. If rays of light, of all refrangibilities, start away from the sun, and then are intercepted by the molecules of a particular substance, which require or can vibrate with a particular wave of light, and if that particular wave of light sets that molecule in vibration, it is clear that that ray, if it comes to us at all, would be considerably enfeebled. We should therefore get, in the solar spectrum, gaps, places where there was no light, when we applied the prism; the bright lines usually seen being images of the slit, we should get a dark line when a particular ray was absent.

That experiment has been tried, and has succeeded admirably. In the solar spectrum there are thousands of these dark lines, and every line represents the action of a particular vibration of a particular set of molecules in the sun's atmosphere; hence, we not only get an idea of the extreme complexity of the solar atmosphere, but of the vast stores of knowledge which have yet to be garnered. These thousands of lines each represent to us a fact. They tell us that we have in the sun precisely such a state as I have last supposed-namely, a very hot something inside, of extremely complicated molecular condition, and that between us and it, in its outer atmosphere, we have a collection of molecules which are stopping the sun's light, and causing black spaces in the portions which would otherwise be absolutely white.

Here, then, finally we have the connection between the biggest body in our part of the universe, about which we know nothing, and the smallest masses of the universe, which we call molecules. Nor is this all-we can add chemistry to physics. The vibrations of iron molecules here teach us the spectrum of iron vapor, let us say, and the considerations already stated enable us, by the fact that these lines are matched exactly in the sun's spectrum, to tell that iron exists there. By 'similar reasoning, the presence of between thirty and forty of our terrestrial metals has already been determined in the sun's atmosphere.

It is not necessary that I should give the history in which the names of Wollaston, Fraunhofer, Angström, Stokes, Balfour Stewart, Kirchhoff, and Bunsen have figured, and will figure to the end of time. The modern work was first fairly under way when physicists concluded that the double line D, one of the lettered lines in the solar spectrum, was due to the absorption of the vapor of

sodium in the sun's atmosphere, for the reason that at that particular part of the spectrum we have when we examine the lines of sodium, exactly the counterpart of the two dark lines in two bright ones. When the molecules of sodium, reduced to its utmost simplicity, are vibrating violently, they give two bright lines; but when the molecules are vibrating less violently, they absorb these lines from the light proceeding from any substance hotter than themselves, and more complicated, that lies behind.

This discovery was utilised with the greatest diligence by the two illustrious German physicists whom I named last, Kirchhoff and Bunsen; and before they had worked long, they got a magnificent proof of the fact that matter throughout space is that particular matter with which we are acquainted here. It was no longer true that every body in the universe might have a law of its own. They could tell that in the sun, at all events, the same laws of physics and chemistry were at work, as those we have gathered from the investigation of terrestrial matter, and thus was the uniformity of nature magnificently established. But that important result was not long before it was almost eclipsed by other results reached by Dr. Huggins in this country. He was not content with observing the sun as they had done. Not hindered by perhaps a thousand times ninety-two millions of miles, he attacked the stars, which the same method taught us were merely distant suns. He was, in a great many instances, able to say that certain lines which were visible in the spectrum of the stars, were visible in the spectrum of the sun; and the work has gone on since as the fruit of many men's work, and nebula, comet, and planet have each in turn been compelled to yield up those secrets which I hope to supply in the following papers.-Good Words.

With silver tips,

Cornhill Magazine.

EDMUND BURKE, whose genius Ireland can claim as entirely her own, was born in a house on Arran Quay, then a fashionable quarter of Dublin, on the 12th of January 1729, new style. His father, Richard Burke, was an attorney of considerable ability and extensive practice, and belonged to the Protestant communion. His mother was a Catholic,'a daughter of Patrick Nagle of Ballyduf, in the county of Cork. Edmund Burke was one of a large family, of whom only himself, two brothers, and one sister attained majority. Very little is known of his early years, except his being of a delicate constitution, which rendered it necessary for him to stay longer than usual under the parental roof. He He was first taught to read by his mother, who was a woman of sound and cultivated understanding. The air of the country, however, being deemed essential to his health, he was removed from Dublin to the house of his grandfather at Castletown Roche, that region of Ireland so intimately associated with Spenser's immortal name. Burke was familiar with the ruined castle where Spenser's great work was moulded into imperishable form, and he too was fond of wandering among the coolly shades of the green alders by the Mulla's shore." At Castletown Roche, Burke spent a considerable time, and it was here that he first went to school. In his twelfth year he was promoted to the Academy of Baltimore, a picturesque village about thirty miles from Dublin. The school was kept by a learned Quaker, Abraham Shackleton, and with the son of the

master Burke formed a close and affectionate friendship, which was only interrupted by the death of Richard Shackleton in 1792. On hearing the news of the loss of his old friend, Burke, then one of the most famous men in Europe, wrote to the sister of his schoolmate :

"I am penetrated with a very sincere affliction, for my loss is great too. I am declining, or, rather, declined in life, and the loss of friends, at no time very reparable, is impossible to be repaired at all in this advanced period. I knew him from the boyish days in which we began to love each other."

After having been three years at the Academy of Baltimore, Burke quitted it, and in April 1744 he was admitted as a pensioner to Trinity College, Dublin. He passed through the usual routine of a university education with credit, but nothing more. He did not waste his time like his contemporary, the gay and tender Goldsmith, in frolic and dissipation, but he spent it in miscellaneous reading. reading. Burke himself wrote:

"Being diligent is the gate by which we must pass to knowledge and fortune; without it we are both unserviceable to ourselves and our fellow-creatures and a burthen to the earth. I have a superficial knowledge of many things, but scarce the bottom of any."

His knowledge of Greek and Latin was never thorough, nor had he any turn for critical niceties. His classical learning was the learning of a man of genius, not of a university pedant. He considered the ancient languages, not as mere instruments for making inferior verses, but as golden keys to ancient thoughts, sentiments, knowledge, and reasoning.