seen.

was observed a few months ago, that astronomers began to think that they would get no other information from comets. It was especially unsatisfactory that no bright or dark lines could be For in the case of one particular class of spectroscopic observations, which seemed specially likely to give interesting information about comets, bright bands in the spectrum are absolutely useless. We refer to those observations which indicate rapid motions of recession or approach, by displacements of the spectrum. Such displacement is always exceedingly small even in the case of bodies moving at the rate of twenty or thirty miles per second. It therefore cannot possibly be determined by observing a spectrum of broad bands of light, with no well-defined edges by which to recognize displace

ment.

But Wells's comet last spring, though it attracted no special attention from ordinary star-gazers, showed for the first time a new and promising feature. This comet, which had shown the carbon bands like other comets during the first month or two of its approach toward the sun after its discovery, began, when it drew within a certain distance from him, to show evidence of the presence of glowing sodium. A few days later the pair of orange lines in the spectrum which indicate the presence of this widely distributed element, were very bright and distinct, and they continued so until the comet passed out of view from our northern heavens.

Now there was double promise in this observation. First, it showed that the changes of appearance which a comet undergoes as it draws nearer to the sun are accompanied by changes of physical condition with which the spectroscope can deal. Secondly, as the bright lines of sodium are well defined, and as their proper place in the spectrum is known, there was promise that hereafter observations might be made to determine movements of recession or of approach which may be taking place either in different parts of the comet, or in the comet as a whole.

Let us first consider the application of spectrum analysis to determine the changes taking place in the physical condition of a comet.

It is obviously a most promising circumstance that evidence should now be attainable to show what is the real physical constitution of those different parts of a comet which present such striking changes as the comet approaches the sun. Hitherto all that has been seen has been the raising up of luminous envelopes on the side toward the sun, and the apparent sweeping away of the matter thus formed into the strange appendage called the tail. But hereafter, in the case of any comet which like Donati's (in 1858) exhibits under favorable conditions the various changes due to the increased proximity of a comet to the sun, it will be found possible to recognize by means of the spectroscope the substances which are successively volatilized as the comet moves toward its perihelion. It may possibly be found that when a comet shows, as Donati's did, several envelopes one within the other, the luminous vapors forming these are of different substance. The constitution of the tail, too, may be found to vary as the comet changes in position. Where there are more tails than one, as in the case of Donati's comet, and of other celebrated comets, the spectroscope may indicate varieties of physical structure and condition. Possibly, Bredichin's theory, that three different substances-iron, carbon, and hydrogen-driven from the sun with different velocities, form the several tails of such comets, may be established by the spectroscopic analysis of these appendages. It may very probably be found, also, that even in the case of a comet with but a single tail, the physical constitution of the tail varies in different parts of its length.

But the possibility that movements in the nucleus, coma, and tail of a comet, may be detected by spectroscopic analysis, is yet fuller of promise.

Let us briefly consider the nature of this method of observation.

When we approach a point from which waves of any sort are moving, we cross the waves in more rapid succession, and the effect is as though they were narrowed. When, on the other hand, we recede from their source, so that the waves (moving, it is understood, more quickly than we do) overtake us, they pass us in less rapid suc

cession, and the effect is as though they were made broader. (We speak, of course, of their width as measured from crest to crest.) We can easily see that this would be so in a sea across which waves were swiftly travelling, a stout swimmer urging his way so as either to meet them or to be overtaken by them. It has been shown, also, experimentally that this is true of sound. When we approach a source of sound, the tone is raised (or rather appears to the ear to be so, for, of course, the sound-waves on which the tone depends are not really altered), whereas when we recede from the source of sound the tone seems lowered. This observation, indeed, may readily be made by any observant person in railway travelling; for it will be noticed that whenever the whistle of a passing engine is sounded the tone falls suddenly, or seems to do so, at the moment when the engine which had been approaching begins (having passed us) to recede. In the case of light, it was long since pointed out by Doppler that a similar effect should be produced, if only the velocity of approach or recession is not too small to be appreciable when compared with the tremendous velocity of light-186,000 miles per second.* The effect would theoretically be a change of colors in the case of light really of a single pure color. For light belonging to the red end of the spectrum is formed by waves of greater length than those which form light belonging to the violet end of the spectrum; and the various colors of the spectrum from the red to the violet end have wave-lengths gradually diminishing from the greatest length at the red end to the least length at the violet. Doppler was bold enough to hope that by this method the colors of the stars might indicate stellar movements of recession or of approach. But of that he should have seen, had he reasoned the matter aright, there was no hope or even possibility. For the light of a star contains rays of all colors from

red to violet, and rays beyond the red on one side, and beyond the violet on the other, which therefore no eye can see. The only effect of any diminution of all the wave-lengths would be that a part of the violet light would be lost as light, but its place would be taken by light from the indigo, that by light from the blue, and so on, the light from the red which became orange being replaced by rays otherwise invisible from beyond the red. And similarly (only the change would be in the other direction) in the case of an increase in all the wave-lengths.

But it was early shown (so far as I know I was the first to refer to the matter publicly, but Dr. Huggins-unknown to me-was working at the very time on the plan indicated) that the lines in the spectrum would be shifted - toward the red in the case of recession from the source of light, and toward the violet in the case of approach toward that source. This displacement can be measured-if great enough, or rather, if not too small; for, in the case of all such motions as are taking place among the stars and planets, the displacement must be very, very small indeed.

Now to comets more than to any other class of celestial bodies this method might, it would seem, be advantageously applied. For not only do comets themselves move during a part of their course around the sun with enormous velocity, but within the comet itself changes take place which seem to imply enormously rapid motions. In particular the development of the tail, although it has not been absolutely demonstrated to be due to repulsive action, yet seems explicable in no other way; and if it is thus caused, the movement of the matter forming the tail must take place with a velocity bringing it well within the application of the spectroscopic method.

But it is essential for the use of this method that the spectrum of the moving body should have well-defined and recognizable lines. Bands, such as those in the spectrum of the comets first observed, are utterly useless for this purpose. Their precise position cannot be determined so that we could be sure of any displacement due to motion. For this purpose we must have a line,

which, when the spectrum is brought side by side with that of a terrestrial substance showing the same line, will be in line with this if the celestial source of light is at rest, and will be recognizably displaced toward the red or toward the blue if that luminous body is receding or approaching respectively.

So that when, last May, Wells's comet suddenly began to show the well-known lines of sodium, promise was at once, and for the first time, afforded, that the problems of cometic changes, in so far as these depend on motions taking place within the comet itself, may before long be solved. We can have very little doubt, for instance, that if such a comet as Donati's were now to appear, and to be studied under favorable conditions during those parts of its course in which it was subject to the most intense disturbing action, the bright lines which would be seen in the comet's spectrum would either by their displacement tell us that the substance of the comet is driven wildly hither and thither in the head and swept swiftly away to form the tail, as it seems to be, or else, by remaining unchanged in position, would show that there are no such movements of disturbance or repulsion.

Now the comet which has recently been seen near the sun has been observed by this method. On September 18, when it was but three degrees (say half a dozen sun-breadths) from the sun on the sky, it was examined in the clear sky of Nice by M. Thollon, a skilful French spectroscopist.

For

The spectrum, notwithstanding the obviously unfavorable conditions under which the observation was made, showed clearly the line (or rather the double line) of sodium. Here, by the way, was at once evidence such as in former times no astronomer could have of the comet's real position in space. merly if a comet was observed anywhere, once only, nothing could be certainly known respecting its position, except that it was somewhere in the line of sight in which it was seen. But if we are right in believing that the sodium in a comet is only vaporized and rendered self-luminous when the comet is near the sun, then the new comet on September 18 was not only shown to lie in a

certain direction, but within certain tolerably narrow limits of distance.

But Thollon observed something else, not quite so satisfactorily as to be absolutely certain of it, but still so as to give a considerable degree of assurance. He says that the line of sodium seemed displaced toward the red. This would indicate recession. Observe here again how the spectroscopic method of determining motions of recession or approach may come in to help the astronomer to determine the position of a comet. Supposing this method should ever be so improved that the exact rate of a comet's motion might be determined by it, then instead of merely ascertaining, in any single observation, the direction in which a comet lies at the moment, the astronomer may learn its direction, something (as we have seen) of its distance, and the rate at which it is moving from or toward the observer. The rate of its thwart motion cannot of course be inferred from the spectroscopic observations directly, yet indirectly it can. For the rate of motion at any given distance from the sun for an orbit of known dimensions is known; now the distance of the comet being partly indicated by the spectroscopic observations, the thwart motion known within the same degree of error. Hence, combining this with our more precise knowledge of the motion of recession or approach, we make a first rather rough approximation to the real motion, both in direction and in amount

is

which would determine the orbit absolutely. Observations made a day or two later will show whether the body really is moving in this orbit; and if the later observations include spectroscopic ones we shall obtain means of testing and correcting the first estimate of the orbit which will practically give us the orbit correctly-much more correctly, at any rate, than it can be deduced by the methods at present in use from observations made on four or five different occasions.*

It may be well, perhaps, in conclusion, to inquire how the comet will act

*Theoretically the orbit of a comet can be deduced from three observations; but practi

cally many observations are required to give anything like accuracy.

ually be absorbed by the sun-a fate which we may consider to be assuredly in store for it before many years, perhaps before many months, are past. First, then, be it noticed that at present there is no tendency toward a diminution of the perihelion distance of the comet, as many seem to imagine. The point of nearest approach will remain nearly at the same distance from the sun, at each return of the comet, so long as the orbit remains eccentric. Only when the velocity in perihelion (or at the point of nearest approach) is so reduced that the centrifugal tendency no longer balances the centripetal force, will there be any approach toward the sun. This amounts to saying that until the orbit is transformed into a circle (when there will be no perihelion at all) there will be no approach toward the sun. When that transformation is effected, there will be approach at every part of the circuit-in other words, the course of the comet will become a spiral, the coils of which will draw closer and closer in toward the sun's surface; the sun will be within the coils, but the comet itself will be in the toils, and its end not far off. As

throughout this approach the comet's substance will be in the form of vapor, there will probably be a rapidly increasing resistance, and hence a rapidly increasing rate of approach toward the sun. Oddly enough, the comet's rate of travelling will be increased notwithstanding this constant resistance, the sun's indrawing action adding more motion than the frictional resistance subtracts. For several days, probably, the comet in each circuit, when off the solar disk, will be a conspicuous object to spectroscopists, though not perhaps visible in the telescope. The comet will appear outside of the sun's disk, first on one side, then on the other, at intervals of about 12 hours-3 hours being the time of circuit of a body close to the sun's surface. As this surface is carried round once in about twenty-five hours, there will be considerable loss of velocity, and resulting heat, in the substance of each part of the comet as it is absorbed. But I believe the whole heat of the sun would be little increased if the whole of the comet were thus absorbed at once; and very little indeed if, as is certain, the absorption take place piecemeal.-Cornhill Magazine.

tune for saying a few words upon some aspects of politics in America, in the hope of giving English readers a fair impression of their true state, and of showing how far any warnings drawn from them are applicable to England. I do so, of course, with the diffidence which every one must feel in attempting to speak of a country that he knows only as a traveller. But a citizen of the United States would, in addressing Englishmen, be exposed to other difficulties hardly less serious than those an Englishman has to face in speaking of America.

What is the picture which not only this novel sets before us? It is the picture of a vast continent, a prosperous, rapidly increasing, and highly civilized nation of fifty-one millions of people, whose government lies in the hands of

a knot of selfish and unprincipled men, some of them accessible to bribes, the rest ready to wink at corruption and to sacrifice honor for the sake of their personal advantage or that of their party. The central figure in the novel is a man of great force of character, but thoroughly vulgar in his ideas, as well as in his oratory; a man who admits and justifies a gross breach of public duty in taking money to "put through " a contract, whose power is based upon intrigue, who has done nothing for the country either as a legislator or an administrator. This man is at the head of his party, a candidate for its nomination to the Presidency of the United States, and not unlikely to be chosen. The other personages are worthy companions of such a chief. Some are weak, most are ignorant and narrowminded, all are vulgar. There is no public spirit, no statesmanlike insight among them. Their chief virtue is devotion to a party which seems to have no principles.

"What a shocking state of things!"' cries the English Pharisee, not without a comfortable reflection that he is not as these Republicans. This, then, is what democracy comes to. This is the result of putting power in the hands of the masses. Men of rank and wealth are driven out of public life; the ignoble mob choose people like themselves to be their representatives; corruption reigns; national interests are sacrificed; national honor forgotten; the morality of the country sinks while its revenues are wasted. And this is what you want to bring Enlgand to, with a lowered county franchise, attacks on the House of Lords, and the Birmingham Caucus.'

One need not be a Tory to be alarmed at such a prospect. If the progress of democracy is to make Silas P. Ratcliffe a fair type of our public men, we had better pause. The present state of things, whatever its faults, is not so bad. But is the picture a true one? That is That is to say, are Silas P. Ratcliffe and his associates fair types of leading politicians in America? and if so, does the dominant position which he holds in United States politics mean the same thing as the premiership of a Silas P. Ratcliffe would mean in England? I am not

going to discuss the matter as a political question. Reasonings from the politics of one country to those of another are interesting and, when wisely used, instructive. But they are also dangerous, for there is always something which makes so great a difference between the two countries as to vitiate any inference except under limitations and qualifications which the ordinary reader does not heed, or soon forgets. And sensible people have, at bottom, a just perception of this, and do not suffer themselves to be much influenced by arguments of the kind. The chief practical use of history is to prevent one from being taken in by historical analogies. My object in these pages is to do what little I can to prevent Englishmen from misjudging America, not to frame any arguments in favor of democratic progress in England. Things in England will proceed on their own path whatever we may read about Republicanism elsewhere, for the forces which move them are large and potent. Apart from this altogether it is to be wished that Englishmen should have just views about the country which is most like their own, and with which their relations are most intimate.

That there are such persons as Silas P. Ratcliffe among the public men at Washington must be admitted. There are such persons in England also, and in every country, monarchical or republican. Any one writing a novel about English public life might fill it with people equally unscrupulous and, in their way, equally successful, and yet might justify every character by pointing to some well-known politician as the original of the portrait. There are persons in the English Parliament, and not merely needy adventurers, but persons of wealth or position, some of whom enjoy titles, conferred or inherited, who are no better, and whom we think no better, than these Washington politicians.

But," it will be said, "these men are very few in England; they are not fair types; they are exceptions, rare exceptions; and in England they never rise to high places. Their schemes are mainly commercial, and do not injure the political interests of the country."