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POPULAR EDUCATOR .
LESSONS IN ASTRONOMY.-IX. a mile, will stand for Saturn; a full-sized cherry, three-quarters THE SOLAR SYSTEM-COMPARATIVE SIZES AND DISTANCES,
of a mile distant, for Uranus; and a plum, a mile and a quarter
off, for Neptune. On this scale the distance of the nearest THE SUN-VULCAN.
fixed star would be about 7,500 miles. The stadent will by this time have become acquainted with As the sun is by far the largest of these bodies, we will many of the more important phenomena of the heavens : we treat of it first, and the question that immediately occurs to us will, therefore, proceed now to notice in detail the principal is, What is the distance of this body? The accurate solution facts relating to those of the heavenly bodies which are our nearest of this question is one of the most important problems in neighbours in space, and
astronomy, as this distanco which belong to the same
is taken as a measure for system, or family group, as
determining the distances does the earth.
and magnitudes of most The following is a list Saturn
other heavenly bodies. The of the principal bodies in
principle of the problem this group :- The Sun,
can easily be understood, which is the common cen.
though, of course, there tre round which they all
are many difficulties in the revolve ; Vulcan, Mercury,
carrying of it out. Sup. and Venus, which are dis
pose an observer, situated tinguished as the inferior
on the line BC (Fig. 16), planets, their orbits being
wishes to ascertain the disincluded within that of the
tance of an inaccessible earth; the Earth; and the
object A; let Ac be the superior planets, Mars, the
visual ray by which it is minor planets, or asteroids,
seen at c; at right angles Jupiter, Saturn, Uranus,
to this lay off another line, and Neptune. Several of these have satellites, or secondary BC, and from B‘measure accurately the angle CBA. We planets, revolving around them; and there are also several know then the distance B C, and the measure of the angles comets which are included as regular members of our system. at B and c; it is easy, therefore, to calculate the angle BAC These will be enumerated hereafter.
and the length of A C. As will at once be seen, the longer BC As we inquire more particularly into the movements of these is, the larger will the angle BAC be, and therefore the less the bodies, Fe ste many striking points of similarity. They all i risk of error in measuring it. When this angle is very small, an more round the sun in the same direction,
exceedingly minute error produces a great and in elliptical paths of no great eccen.
difference in the calculated length of C A. tricity. They are all likewise opaque
Now, in the practical application of this bodies like the earth, shining only by re
principle, the utmost base-line that can lected light; and all rotate on their axes,
be obtained is the earth's diameter ; and so as to produce the changes of day and
this is so small in comparison with the night. Their orbits, too, are all inclined
distance of the sun that the angle BAC to the plane of the ecliptic.
becomes too minute to be measured di. Orreries are frequently constructed, in
rectly with a sufficient degree of accuwhich the different planets are represented
racy. We are enabled, however, in an by different-sized balls moving at various
indirect way, to measure it, and thus solve distances round a central one. It
the problem. The planet Venus is, however, quite impossible to
travels round the sun in an orbit make these on a scale at all true
within that of the earth, and to natare. Fig. 15 illustrates A
hence, at certain intervals, passes ronghly their comparative sizes.
between the earth and the sun, The following, however, is a plan
and produces what is called a for obtaining a tolerably correct
transit of the planet. On these idea of their comparative distances B
occasions it is seen as a black and magnitudes, and the relative
spot on the bright disc of the sun, dimensions of their orbits :
and by means of observations Select a large clear space, and
taken at that moment the replace at one side a ball about two feet in
quired angle may be measured. diameter to represent the sun ; Vulcan will
Fig. 17 will render the mode of proceeding then be represented by a small pin's head 27
more clear. A B represents a base-line on feet from the globe; Mercury by a mustard-seed 82 feet | the earth's surface, and CD the sun, E being the planet distant; Venus by a pea at a distance of 142 feet; the Earth by Venus when passing between the two. To an observer at a slightly larger pea at a distance of 215 feet; Mars by a large B it will appear to travel across the sun's disc along pin's head at a distance of 327 feet; the minor planets by grains the line uk, while to one situated at a it will pass along of sand between 500 and 600 feet distant. An orange, about 2 FG. Now if Venus were midway between the earth and the inches in diameter, and 1,120 feet distant, will then represent sun, no advantage would be gained, as the angle MBL would Jupiter ; one about two inches in diameter, distant two-fifths of then be equal at A L B. The planet's distance from the sun is, VOL. V.
however, about two and a half times as great as its distance when the number is at a minimum; the surface being then free from the earth, and hence the angle to be measured is so much from them on more than half the days of observation. They greater.
then increase again in number for the next five and a-half years ; Now by accurately observing the times of the planet first and thus their period appears to be about eleven years. A most coming into contact with the sun's disc at n, and of again remarkable fact has been noted in connection with this, and emerging from it at K, we shall know exactly the length of Hk; that is, that the daily variation in the magnetic needle is found in a similar way, another observer can ascertain the length of to have a precisely similar period, and to increase or diminish the chord F G, and thus we can learn the exact length of the with the increase or diminution in the numbers of spots. line ML, and the measure of the angle M B L.
Other phenomena seem further to show that there is an inti. Of course, many of the details are omitted here, but the mate relationship between the movements of the magnetic student should make himself master of the principle of the needle and the sun. Whether or not future observations may calonlation, as being the key to all celestial measurements. So reveal to us more of the nature of this bond, we cannot say, great is the importance attached to this problem that at the but fresh discoveries on the subject are frequently being last transit, in 1769, several expeditions were sent out by made. Government to take observations at different stations.
These spots are usually accounted for by supposing the sun As a result of the most accurate observations, the sun's to be a dark opaque body surrounded by two atmospheres, the horizontal parallax--that is, the angle that would be subtended outer one highly luminous, and the inner one more denso. It is to an observer in the sun by the semi-diameter of the earth-supposed then that some powerful internal convulsion breaks is found to be about 8:93“, and the mean distance of the sun is through these layers, and thus reveals the dark surface of the therefore about 91,430,000 miles. Until quite recently the sun beneath. parallax was taken at 8:6", and the sun's distance set down at In addition to these dark spots, others of unusual brilliancy 95,000,000 miles, but subsequent investigations have shown an are frequently observed. These are termed faculo. Telescopio error in these measurements. The numbers given above must, investigations show that, besides these markings, the whole however, be taken as approximations only, subject to future surface has somewhat of a mottled appearance. According to correction. The next transit of Venus, which will occur in Nasmyth, it presents an appearance as if it were covered over December, 1874, is anxiously awaited to settle the question with scattered filaments shaped like willow-leaves. The whole decisively. It must be remembered that the distance given question of the physical constitution of the sun is, however, above is the mean, the difference between the minimum and the engaging the attention of many astronomers. A total eclipse maximum being about 3,000,000 miles.
of the sun presents good opportunities for the observation of Having ascertained the distance of the sun, and knowing its many points, and among the most remarkablo features in conapparent diameter to be about 32', it becomes a simple pro- nection with these phenomena is the appearance of red flames blem to ascertain its real magnitude ; and in this way we find or protuberances surrounding the dark body of the moon at that its diameter is about 853,000 miles, or more than 108 the moment of total obscuration. These have recently been times as great as that of the earth. The best idea we can give seen at other times also, and are believed to be connected with of this immense size, is to state that if the sun were hollow, the solar atmosphere. The symbol O is frequently employed and the earth were placed in its centre, there would be room in almanacks to denote the sun. enough for the moon to continue to revolve round it without We now pass on to notice the planets which revolve in ceasetouching the sun's surface, even if the moon's distance were less courses around this grand central luminary. Till recently, increased to nearly double what it is now. . The sun's volume Mercury was supposed to be the nearest planet to the sun. is so great that it would require 1,300,000 globes of the size of About ten years ago, however, the celebrated French astronomer, the earth to be rolled into one to equal it, and it is 450 times as Le Verrier, having very carefully examined the movements of large as all the planets that revolve around taken together. this planet, found in it a slight variation, which he could
Some idea can be formed of its light and heat when we only account for by supposing that the mass of the planet remember the enormous distance we are from its surface, and Venus was incorrectly ascertained, or else that there was a the degree to which, notwithstanding this, we feel its power. planet revolving round the sun in an orbit within that of Its light is computed to be equal to that of 5,500 standard Mercury. candles, placed at a distance of a foot from the surface to be These statements of his were published in the hope that some illuminated.
further light might be thrown on the matter. It must be reWe naturally want to know something more of the physical membered, however, that Mercury itself can only be seen at properties of this wonderful and stupendous orb, but we are to occasional intervals, and with difficulty, owing to its proximity a great extent baffled in this inquiry, though many great and to the sun; and that therefore a planet much nearer to the sun important discoveries have been recently effected by means of would never be far enough removed from that body to be clearly spectrum analysis. In this way it has been ascertained that many Almost the only opportunity, then, of observing it would of the metals present in the earth are also present in the sun. be when it was in transit.
When pieces of very dark glass are placed in front of the As soon as Le Verrier had made his statement, a French phy. eye-piece of a telescope, so as to screen the eye from the sician named Lescarbault stated that on the 26th of March, 1859, intense glare of the sun, its surface may be carefully examined, he had seen a small body pass.across the sun, but had not liked and is found to present an appearance by no means uniform. to announce the fact, no other observer having called attention Many dark spots (Fig. 18), termed maculce, are found at times to it. Le Verrier at once saw him, and carefully inquired into to exist upon its surface. The centre of these is usually of a the matter. At first he thought the whole affair was a delusion: very dark colour, and is surrounded by a ring much lighter in but after questioning the physician, and inquiring about tho appearance, which is known as the penumbra. These spots apparatus he used, he became convinced that he had indeed are very irregular in shape, and frequently change in size or discovered a new planet, which was then called Vulcan. From disappear altogether. At times, however, they remain per- this one observation no very decisive details could be drawn, manent sufficiently long to be traced disappearing at one edge so as to calculate its orbit accurately; its distance from tho of the disc, and after an interval appearing again at the sun was, however, set down at about 14,000,000 miles, and its other. We thus learn that the sun, like the other members time of revolution in its orbit at a little under twenty days. It of our system, is in constant rotation on its axis, and the was conjectured that a second transit might be observed in period of this rotation is found to be 25 days, 7 hours, and March, 1860; but though a careful watch was kept, it was not 48 minutes.
seen, nor has it been seen again up to the present time. Many, These spots are occasionally so large as to be distinctly on this account, treat the whole affair as a mistake. Instances observed by the naked eye. Some of them have been measured, have, however, been previously recorded of spots resembling and their breadth found to be more than 100,000 miles. Most planets being seen on the sun, and it may be that futare observaof them, however, are only visible with the aid of the tele- tions will show that the planet really exists, and that these have scope. Careful records have been kept of the appearance of been transits. We cannot, however, give definite statement these spots, and it is found that during some years there is either way, so we merely thus briefly state the fact of the alleged scarcely a day elapses without some being visible. They then discovery, and shall commence our next lesson with some acdiminish in frequency for about five or five and a half years, I count of Mercury, the next planet in order of distance.
HISTORIC SKETCHES. --XLIV.
a pure theocracy—that is, of a form of government in which
God is the central figure, the head from whom all orders emanate, THE JEWS.-I.
and to whom all accounts of orders executed are rendered. So intimately is the history of the Jews bound up with the As the representative of God, and the declarator of His word, Holy Seripture narrative, that few persons accustom themselves a prophet was to be obeyed implicitly whenever he spoke proto read the two as distinct. In one sense, of course they fessionally, his authority superseding even that of the king are not distinct. The Jewish history, like the rest of the old where the two conflicted. It was natural enough that the Testament, was written for our learning, and is profitable for statesman on the throne should dislike, and vehemently dislike, **instruction in righteousness."
this sort of imperium in imperio. So long as king and prophet It is the very groundwork, so to speak, of the Bible. Yet agreed, which they seldom did, upon the course of government, is it well sometimes to consider the remarkablo history of this all went smoothly, and the spiritual power came in with might remarkable people apart from its surroundings, to learn from to the aid of the temporal; but whenever there was a conflict, it the meaning of its intense individuality, and to see that it was war to the knife. Unfortunately for the people, they had no more been patent to the world than the marvellous were seldom on the prophet's side, inclining more frequently to series of facts from the delivery out of Egypt to the establish- take the part of the prince of this world—who, so long as they ment of Sanl upon the throne, men must have been led to the paid taxes and gave recruits for the army, allowed them to do conclasion that some special providence watched over the pretty much as they pleased rather than the part of the servant national life of the Jews, and that the Jews were a chosen of Jehovah, who, for all that he had brought them out of people, specially favoured of the Divine Ruler of the universe. Egypt, and blessed them in many things beside, was too highly Most of the earlier Jewish history is derived from the Bible, exalted out of their reach for them to have sympathy. with but the later portions are drawn from many sources from the Him, and who was also of purer eyes than to behold iniquity. histories of people who made a great figure in the world till Instances of conflicts of this sort are many and flagrant in the they bruised themselves against the rock of Jewish nationality course of the Old Testament Scriptures, from which it will and were overthrown by it-from the histories of peoples who also be seen that it was a natural tendency in the people to finally dispossessed the chosen people, and cast them forth as * start aside like a broken bow” whenever the yoke of the wanderers upon the face of the earth till the time of their Divine King was laid upon them for their good. It was in redemption shall draw nigh. It is proposed in this and one or consequence of this tendency that a temporal king became two sposeeding sketches, to portray the Jews as they appeared necessary. at distinct epochs in their history, with a view to directing Let us, before considering the constitution of the kingdom of attention to the special features of their case, and to induce Israel, sketch briefly the principal features of Jewish history our readers to pursue more closely for themselves the study up to the time when a king was demanded. Certain Arabs, of the most remarkable history known to the experience of the known to us in Biblical writings as the sons of Jacob, fed world.
their flocks and herds in the country westward of Lower Egypt, * And all the people shouted and said, God save the king." and led the nomadic life of shepherds in a land barely fruitful It is a new cry in Israel. Up to that time the Jews had been enough to support them. This difficulty naturally increased content to live under the political guidance of spiritual chiefs, with the increase of population, and at times the chiefs seting for and in behalf of that Divine Ruler who had brought were straitened to know what to do for food. These chiefs then out of Egypt with a mighty hand and a stretched-out were non-elective heads of families, exercising despotic power sem. Now they wearied of the unseen King who never held over children and children's children, their authority being courts, nor entertained, nor showed himself, save in a figurative checked only by fear of physical resistance in their subjects. way, but who yet kept awful state in the midst of the people, They were what Tartar or Arab chiefs are in the present daybeing made manifest sometimes in the storm, sometimes in patriarchial rulers, governing not according to any fixed law, the whirlwind, and to those few who could understand Him in but giving judgment according to discretion upon each case as that guire, in the still, small voice. So “Samuel took a vial it arose. of oil, and poured it apon Saul's head, and kissed him, and It so happened that about the year B.c. 1706 a drought of unsaid, Is it not because the Lord hath anointed thee to be usual severity forced these Arabs to look yond their own imcaptain over his inheritance ?" and at Mizpeh Samuel collected mediate compounds for sustenance for themselves and their little the people and announced what he had done, reproaching them ones. Many of the cattle and sheep died, and it was becoming at the same time for having rejected the God “who himself a question of human lives also. .To the neighbouring land of sared you out of all your adversities and your tribulations,” Egypt the eyes of the Arabs were turned; the dread of famine od for having said, “Nay, but set a king over us. Saul overcame their repugnance to mix with people alien to them. was ancinted, the multitude shouted “God save the king,” and selves, and some of the great chief's sons were sent down by the first step was taken towards divorcing the State, not from their father to buy the necessary supplies in the fruitful land the Church merely, but from the Head of the Church, from God of Egypt. Egypt was the market in which they had been himself.
accustomed to sell the surplus of their own stocks. It was Those who may have noticed it as a curious thing, when already known to them commercially and by repate as one of reading the historical books of the Old Testament, that the the most flourishing and richest countries in. the world. Perifunctions of the prophet should have been allowed to clash odically it had been their practice to send down thither, and we with the functions of the king, and that what must often have have mention made in the Bible of some of these visits. looked like insolence was tolerated, in appearance at least, Generally, however, they did their business through agents, when it came from the month of a man of God, would do well merchants who came up expressly from Egypt to deal with the to call to mind the peculiar relationship in which prophet and wanderers, and returned with their purchases in a caravan. Το king stoed to each other. Historically considered, the prophet such dealers, a short while before the famine alluded to, the was the creator of the king, the ruler who had governed before sons of Jacob sold their younger brother Joseph, against whom eter the idea of monarchical government had entered the they had a jealousy; and from such dealers they would gladly mind of the Jewish leaders; the man who, having given, might have bought all the supplies of food they needed. But the be suppoked to have some power also to take away. The famine was so sore in the land that the merchants would not prophet was the avowed oracle of God; the king was a con- come up into it, and those who sought produce from Egypt cordion to the desire of the people-a desire which was er were therefore compelled to go down into that land and seek pressed in direct contravention of the will of the Almighty, it there. The sons of Jacob went down, under the circumThe Igelitish people could not remain satisfied with a system stances so familiar readers the Old Testament histo of government which differed in so remarkable a manner from and found “corn in Egypt.” This was sold to them by the that of the nations by whom they were surrounded, and, in governor of the province, who proved to be their own brother, site of Samuel's urgent advice, they persisted in asking for and whose excellent behaviour and able administration hadi sing. Still it must be borne in mind that, in spite of this won for him the rulership over many cities, and the right of est the principles of government which prevailed among entry into the joy of his lord. the Inselites from the time they came out of Egypt to the Political circumstances, which were stated at length in the period when they ceased to be a collective nation, were those of Historic Sketch of Ancient Egypt (Vol. IV., page 222), in