Chapter VIII: Description of Celestial Objects Mentioned in 'paradise Lost' (1)

THE SUN

The surpassing splendour of the Sun, as compared with that of any of the other orbs of the firmament, is not more impressive than his stupendous magnitude, and the important functions which it is his prerogative to fulfil. Situated at the centre of our system--of which he may be regarded as 'both eye and soul'--the orb has a diameter approaching 1,000,000 miles, and a mass 750 times greater than that of all the planets combined. These, by his attractive power, he retains in their several paths and orbits, and even far distant Neptune acknowledges his potent sway. With prodigal liberality he dispenses his vast stores of light and heat, which illumine and vivify the worlds circling around him, and upon the constant supply of which all animated beings depend for their existence. Deprived of the light of the Sun, this world would be enveloped in perpetual darkness, and we should all miserably perish.

The Sun is distant from the Earth about 93,000,000 miles. His diameter is 867,000 miles, or nearly four times the extent of the radius of the Moon's orbit. The mass of the orb exceeds that of the Earth 330,000 times, and in volume 1,305,000 times. The Sun is a sphere, and rotates on his axis from west to east in 25 days 8 hours. The velocity of a point at the solar equator is 4,407 miles an hour. The density of the Sun is only one-fourth that of the Earth, or, in other words, bulk for bulk, the Earth is four times heavier than the Sun. The force of gravity at the Sun's surface is twenty-seven times greater than it is on the Earth; it would therefore be impossible for beings constituted as we are to exist on the solar surface.

The dazzling luminous envelope which indicates to the naked eye the boundary of the solar disc is called the PHOTOSPHERE. It is most brilliant at the centre of the Sun, and diminishes in brightness towards the circumference, where its luminosity is but one-fourth that of the central portion of the disc. The photosphere consists of gaseous vapours or clouds, of irregular form and size, separated by less brilliant interstices, and glowing white with the heat derived from the interior of the Sun. In the telescope the photosphere is not of uniform brilliancy, but presents a mottled or granular appearance, an effect created by the intermixture of spaces of unequal brightness. Small nodules of intense brilliance, resembling 'rice-grains,' but which, according to Nasmyth, are of a willow-leaf shape with pointed extremities, which form a network over portions of the photosphere, are sprinkled profusely over a more faintly luminous background. These 'grains' consist of irregular rounded masses, having an area of several hundred miles. By the application of a high magnifying power they can be resolved into 'granules'--minute luminous dots which constitute one-fifth of the Sun's surface and emit three-fourths of the light. This granulation is not uniform over the surface of the photosphere; in some parts it is indistinct, and appears to be replaced by interlacing filamentous bands, which are most apparent in the penumbrae of the spots and around the spots themselves. The 'granules' are the tops of ascending masses of intensely luminous vapour; the comparatively dark 'pores' consist of similar descending masses, which, having radiated their energy, are returning to be again heated underneath the surface of the photosphere.

In certain regions of the photosphere several dark patches are usually visible, which are called 'sun-spots.' At occasional times they are almost entirely absent from the solar disc. It has been observed that they occupy a zone extending from 10 deg. to 35 deg. north and south of the solar equator, but are not found in the equatorial and polar regions of the Sun. A sun-spot is usually described as consisting of an irregular dark central portion, called the _umbra_; surrounding it is an edging or fringe less dark, consisting of filaments radiating inwards called the _penumbra_. Within the umbra there is sometimes seen a still darker spot, called the _nucleus_. The umbra is generally uniformly dark, but at times filmy luminous clouds have been observed floating over it. The nucleus is believed to be the orifice of a tubular depression in the floor of the umbra, prolonged downwards to an unknown depth. The penumbra is brightest at its inner edge, where the filaments present a marked contrast when compared with the dark cavity of the umbra which they surround and overhang. Sometimes lengthened processes unite with those of the opposite side and form bands and 'bridges' across the umbra. The darkest portion of the penumbra is its external edge, which stands out conspicuously against the adjoining bright surface of the Sun. One penumbra will sometimes enclose several umbrae whilst the nuclei may be entirely wanting.

(_Janssen._)]

Sun-spots usually appear in groups; large isolated spots are of rare occurrence, and are generally accompanied by several smaller ones of less perfect formation. The exact moment of the origin of a sun-spot cannot be ascertained, because it arises from an imperceptible point; it grows very rapidly, and often attains its full size in a day.

Prior to its appearance there is an unusual disturbance of the solar surface over the site of the spot: luminous ridges, called _faculae_, and dark 'pores' become conspicuous, between which greyish patches appear, that seem to lie underneath a thin layer of the photosphere; this is rapidly dispelled and a fully formed spot comes into view. When a sun-spot has completed its period of existence, the photospheric matter overwhelms the penumbra, and rushes into the umbra, which it obliterates, causing the spot to disappear. The duration of sun-spots is subject to considerable variation; some last for weeks or months, and others for a few days or hours. A spot when once fully formed maintains its shape, which is usually rounded, until the period of its breaking up. Spots of long duration rotate with the Sun. Those which become visible at the edge of the Sun's limb have been observed to travel across his disc in less than a fortnight, disappearing at the margin of the opposite limb; afterwards, if sufficiently long-lived, they have reappeared in twelve or thirteen days on the surface of the orb where first observed. It was by observation of the spots that the period of the axial rotation of the Sun became known.

Sun-spots vary very much in size--some are only a few hundred miles in width, whilst others have a diameter of 40,000 or 50,000 miles or upwards. In some instances the umbra alone has a breadth of 20,000 or 30,000 miles--three times the extent of the diameter of the Earth. Spots of this size are visible to the naked eye when the Sun is partially obscured by fog, or when his brilliancy is diminished by vapours near the horizon. A year seldom passes without the occurrence of several of such spots being recorded. The largest sun-spot ever observed had a diameter of about 150,000 miles. A group of spots, including their penumbrae, will occupy an area of many millions of square miles.

By long observation it has been ascertained that sun-spots increase and diminish in number with periodical regularity, and that a maximum sun-spot period occurs at the end of each eleven years. When spots are numerous on the Sun's disc there is great disturbance of the solar surface, accompanied by fierce rushes of intensely heated gases. This solar activity is known to influence terrestrial magnetism by causing a marked oscillation of the magnetic needle, and giving rise to so-called 'magnetic storms,' accompanied by magnificent displays of aurorae, with variations in electrical earth-currents. It would therefore appear that sun-spots have a pronounced effect upon magnetic terrestrial phenomena, but how this is produced remains unknown.

Besides sun-spots, there are seen on the solar disc bright flocculent streaks or ridges of luminous matter called _faculae_; they are found over the whole surface of the Sun, but are most numerous near the limb and in the immediate vicinity of the spots. They have been compared to immense waves--vast upheavals of photospheric matter, indicative of enormous pressure, and often extending in length for many thousands of miles.

Nearly all observers have arrived at the conclusion that sun-spots are depressions or cavities in the photosphere, but considerable difference of opinion exists as to how they are formed. The most commonly accepted theory is that they are caused by the pressure of descending masses of vapour having a reduced temperature, which absorb the light and prevent it reaching us. Our knowledge of the Sun is insufficient to admit of any accurate conclusion on this point; though we are able to perceive that the surface of the orb is in a state of violent agitation and perpetual change, yet his great distance and intense luminosity prevent our capability of perceiving the ultimate minuter details which go to form the _texture_ of the solar surface. 'Bearing in mind that a second of arc on the Sun represents 455 miles, it follows that an object 150 miles in diameter is about the _minimum visible_ even as a mere mathematical point, and that anything that is sufficiently large to give the slightest impression of shape and extension of surface must have an area of at least a quarter of a million square miles; ordinarily speaking, we shall not gather much information about any object that covers less than a million.'[13] Since the British Islands have only an area of 120,700 square miles, it is evident that on the surface of the Sun there are many phenomena and physical changes occurring which escape our observation. Though the changes which occur in the spots and faculae appear to be slow when observed through the telescope, yet in reality they are not so. Tremendous storms and cyclones of intensely heated gases, which may be compared to the flames arising from a great furnace, sweep over different areas of the Sun with a velocity of hundreds of miles an hour. Vast ridges and crests of incandescent vapour are upheaved by the action of internal heat, which exceeds in intensity the temperature at which the most refractory of terrestrial substances can be volatilised; and downrushes of the same photospheric matter take place after it has parted with some of its stores of thermal energy. Sun-spots of considerable magnitude have been observed to grow rapidly and then disappear in a very short period of time; occasionally a spot is seen to divide into two or more portions, the fragments flying asunder with a velocity of not less than 1,000 miles an hour. It is by these upheavals and convulsions of the solar atmosphere that the light and heat are maintained which illumine and vivify the worlds that gravitate round the Sun.

During total eclipses of the Sun, several phenomena become visible which have enabled astronomers to gain some further knowledge of the nature of the solar appendages. The most important of these is the CHROMOSPHERE, which consists of layers of incandescent gases that envelop the photosphere and completely surround the Sun. Its average depth is from 5,000 to 6,000 miles, and when seen during an eclipse is of a beautiful rose colour, resembling a sheet of flame. As seen in profile at the edge of the Sun's disc, it presents an irregular serrated appearance, an effect created by the protuberance of luminous ridges and processes--masses of flame which arise from over its entire surface. The chromosphere consists chiefly of glowing hydrogen, and an element called _helium_, which has been recently discovered in a terrestrial substance called cleveite; there are also present the vapours of iron, calcium, cerium, titanium, barium, and magnesium. From the surface of this ocean of fire, jets and pointed spires of flaming hydrogen shoot up with amazing velocity, and attain an altitude of ten, twenty, fifty, and even one hundred thousand miles in a very short period of time. They are, however, of an evanescent nature, change rapidly in form and appearance, and often in the course of an hour or two die down so as not to be recognisable. These _prominences_, as they are called, have been divided into two classes. Some are in masses that float like clouds in the atmosphere, which they resemble in form and appearance; they are usually attached to the chromosphere by a single stem, or by slender columns; occasionally they are entirely free. These are called _quiescent_ prominences; they consist of clouds of hydrogen, and are of more lasting duration than the other variety, called _eruptive_ or metallic prominences. The latter are usually found in the vicinity of sun-spots, and, besides hydrogen, contain the vapours of various metals. They are of different forms, and present the appearance of filaments, spikes, and jets of liquid fire; others are pyramidal, convoluted, and parabolic.

These outbursts, bending over like the jets from a fountain, and descending in graceful curves of flame, ascend from the surface of the chromosphere with a velocity often exceeding 100 miles in a second, and frequently reach an enormous height, but are of transient duration. They are closely connected with sun-spots, and are evidence of the tremendous forces that are in action on the surface of the Sun.

The CORONA is an aureole of light which is seen to surround the Sun during a total eclipse. It is an impressive and beautiful phenomenon, and is only visible when the Sun is concealed behind the dark body of the Moon. Professor Young gives the following graphic description of the corona: 'From behind it [the Moon] stream out on all sides radiant filaments, beams, and sheets of pearly light, which reach to a distance sometimes of several degrees from the solar surface, forming an irregular stellate halo, with the black globe of the Moon in its apparent centre. The portion nearest the Sun is of dazzling brightness, but still less brilliant than the prominences, which blaze through it like carbuncles. Generally this inner corona has a pretty uniform height, forming a ring three or four minutes of arc in width, separated by a somewhat definite outline from the outer corona, which reaches to a much greater distance and is far more irregular in form. Usually there are several "rifts," as they have been called, like narrow beams of darkness, extending from the very edge of the Sun to the outer night, and much resembling the cloud shadows which radiate from the Sun before a thundershower. But the edges of these rifts are frequently curved, showing them to be something else than real shadows. Sometimes there are narrow bright streamers as long as the rifts, or longer. These are often inclined, or occasionally even nearly tangential to the solar surface, and frequently are curved. On the whole, the corona is usually less extensive and brilliant over the solar poles, and there is a recognisable tendency to accumulation above the middle latitudes, or spot zones; so that, speaking roughly, the corona shows a disposition to assume the form of a quadrilateral or four-rayed star, though in almost every individual case this form is greatly modified by abnormal streamers at some point or other.' The corona surrounds the Sun and its other envelopes to a depth of many thousands of miles. It consists of various elements which exist in a condition of extreme tenuity; hydrogen, helium, and a substance called coronium appear to predominate, whilst finely divided shining particles of matter and electrical discharges resembling those of an aurora assist in its illumination.

We possess no knowledge of the physical structure of the interior of the Sun, nor have we any terrestrial analogy to guide us as to how matter would behave when subjected to such conditions of extreme temperature and pressure as exist in the interior of the orb. Yet we are justified in concluding that the Sun is mainly a gaseous sphere which is slowly contracting, and that the energy expended in this process is being transformed into heat so extreme as to render the orb a great fountain of light.

Milton in his poem makes more frequent allusion to the Sun than to any of the other orbs of the firmament, and, in all his references to the great luminary, describes him in a manner worthy of his unrivalled splendour, and of his supreme importance in the system which he upholds and governs. After having alighted on Mount Niphates, Satan is described as looking

Sometimes towards Heaven and the full-blazing Sun,
Which now sat high in his meridian tower.--iv. 29-30.

He then addresses him thus:--

O thou that with surpassing glory crowned,
Look'st from thy sole dominion like the god
Of this new World--at whose sight all the stars
Hide their diminished heads--to thee I call,
But with no friendly voice, and add thy name,
O Sun, to tell thee how I hate thy beams,
That bring to my remembrance from what state
I fell, how glorious once above thy sphere.--iv. 32-39.

On another occasion:--

The golden Sun in splendour likest Heaven
Allured his eye.--iii. 572-73.

In describing the different periods of the day, Milton seldom fails to associate the Sun with these times, and rightly so, since they are brought about by the apparent diurnal journey of the orb across the heavens. Commencing with morning, he says:--

Meanwhile,
To re-salute the world with sacred light,
Leucothea waked, and with fresh dews embalmed
The Earth.--xi. 133-36.

Soon as they forth were come to open sight
Of day-spring, and the Sun--who, scarce up-risen,
With wheels yet hovering o'er the ocean-brim,
Shot parallel to the Earth his dewy ray,
Discovering in wide landskip all the east
Of Paradise and Eden's happy plains.--v. 138-43

or some renowned metropolis
With glistering spires and pinnacles adorned,
Which now the rising Sun gilds with his beams.--iii. 549-51.

while now the mounted Sun
Shot down direct his fervid rays, to warm
Earth's inmost womb.--v. 300-302.

for scarce the Sun
Hath finished half his journey, and scarce begins
His other half in the great zone of Heaven.--v. 558-60.

To sit and taste, till this meridian heat
Be over, and the Sun more cool decline.--v. 369-70.

And the great Light of Day yet wants to run
Much of his race, though steep. Suspense in Heaven,
Held by thy voice, thy potent voice he hears,
And longer will delay, to hear thee tell
His generation, and the rising birth
Of Nature from the unapparent deep.--vii. 98-103.

The declining day and approach of evening are described as follows:--

Meanwhile in utmost longitude, where Heaven
With Earth and Ocean meets, the setting Sun
Slowly descended, and with right aspect
Against the eastern gate of Paradise
Levelled his evening rays.--iv. 539-43.

the Sun now fallen
Beneath the Azores; whether the Prime Orb,
Incredible how swift, had thither rolled
Diurnal, or this less volubil Earth,
By shorter flight to the east, had left him there
Arraying with reflected purple and gold
The clouds that on his western throne attend.--iv. 591-97.

the parting Sun
Beyond the Earth's green Cape and verdant Isles
Hesperian sets, my signal to depart.--viii. 630-32.

Now was the Sun in western cadence low
From noon, and gentle airs due at their hour
To fan the Earth now waked, and usher in
The evening cool.--x. 92-95.

for the Sun,
Declined, was hasting now with prone career
To the Ocean Isles, and in the ascending scale
Of Heaven the stars that usher evening rose.--iv. 352-55.

In the combat between Michael and Satan, which ended in the overthrow of the rebel angels, Milton, in his description of their armour, says:--

two broad suns their shields
Blazed opposite.--vi. 305-306,

and in describing the faded splendour of the ruined Archangel, the poet compares him to the Sun when seen under conditions which temporarily deprive him of his dazzling brilliancy and glory:--

as when the Sun new-risen
Looks through the horizontal misty air
Shorn of his beams, or, from behind the Moon
In dim eclipse, disastrous twilight sheds
On half the nations, and with fear of change
Perplexes monarchs.--i. 594-99.

This passage affords us an example of the sublimity of Milton's imagination and of his skill in adapting the grandest phenomena in Nature to the illustration of his subject.

THE MOON

The Moon is the Earth's satellite, and next to the Sun is the most important of the celestial orbs so far as its relations with our globe are concerned. Besides affording us light by night, the Moon is the principal cause of the ebb and flow of the tide--a phenomenon of much importance to navigators. The Moon is almost a perfect sphere, and is 2,160 miles in diameter. The form of its orbit is that of an ellipse with the Earth in the lower focus. It revolves round its primary in 27 days 7 hours, at a mean distance of 237,000 miles, and with a velocity of 2,273 miles an hour. Its equatorial velocity of rotation is 10 miles an hour. The density of the Moon is 3.57 that of water, or 0.63 that of the Earth; eighty globes, each of the weight of the Moon, would be required to counterbalance the weight of the Earth, and fifty globes of a similar size to equal it in dimensions. The orb rotates on its axis in the same period of time in which it accomplishes a revolution of its orbit; consequently the same illumined surface of the Moon is always directed towards the Earth. To the naked eye the Moon appears as large as the Sun, and it very rapidly changes its form and position in the sky. Its motions, which are of a very complex character, have been for many ages the subject of investigation by mathematicians and astronomers, but their difficulties may now be regarded as having been finally overcome.

The phases of the Moon are always interesting and very beautiful. The orb is first seen in the west, after sunset, as a delicate slender crescent of pale light; each night it increases in size, whilst it travels eastward, until it attains the figure of a half moon; still growing larger as it pursues its course, it finally becomes a full resplendent globe, rising about the time that the Sun sets and situated directly opposite to him. Then, in a reverse manner, after full moon, it goes through the same phases, until, as a slender crescent, it becomes invisible in the solar rays; afterwards to re-appear in a few days, and, in its monthly round, to undergo the same cycle of changes. The phases of the Moon depend upon the changing position of the orb with regard to the Sun. The Moon shines by reflected light derived from the Sun, and as one half of its surface is always illumined and the other half totally dark, the crescent increases or diminishes when, by the Moon's change of position, we see more or less of the bright side. Visible at first as a slender crescent near the setting Sun, the angular distance from the orb and the width of the crescent increase daily, until, at the expiration of seven days, the Moon is distant one quarter of the circumference of the heavens from the Sun. The Moon is then a semi-circle, or in quadrature. At the end of other seven days, the distance of the Moon from the Sun is at its greatest--half the circumference of its orbit. It is then visible as a circular disc and we behold the orb as full moon. The waning Moon, as it gradually decreases, presents the same aspects reversed, and, finally, its slender crescent disappears in the Sun's rays. The convex edge of the crescent is always turned towards the Sun. The rising of the Moon in the east and its setting in the west is an effect due to the diurnal rotation of the Earth on her axis, but the orb can be perceived to have two motions besides: one from west to east, which carries it round the heavens in 29.53 days, and another from north to south. The west to east motion is steady and continuous, but, owing to the Sun's attractive force, the Moon is made to swerve from its path, giving rise to irregularities of its motion called PERTURBATIONS. The most important of these is the _annual equation_, discovered by Tycho Brahe--a yearly effect produced by the Sun's disturbing influence as the Earth approaches or recedes from him in her orbit; another irregularity, called the _evection_, is a change in the eccentricity of the lunar orbit, by which the mean longitude of the Moon is increased or diminished. _Elliptic inequality_, _parallactic inequality_, the _variation_, and _secular acceleration_, are other perturbations of the lunar motion, which depend directly or indirectly on the attractive influence of the Sun and the motion of the Earth in her orbit.

As the plane of the Moon's orbit is inclined at an angle of rather more than 5 deg. to the ecliptic, it follows that the orb, in its journey round the Earth, intersects this great circle at two points called the 'Nodes.' When crossing the ecliptic from south to north the Moon is in its ascending node, and when crossing from north to south in its descending node. In December the Moon reaches the most northern point of its course, and in June the southernmost. Consequently we have during the winter nights the greatest amount of moonlight, and in summer the least. In the evenings the moonlight is least in March and greatest in September, when we have what is called the Harvest Moon.

The telescopic appearance of the Moon is very interesting and beautiful, especially if the orb is observed when waxing and waning. As no aqueous vapour or cloud obscures the lunar surface, all its details can be perceived with great clearness and distinctness. Indeed, the topography of the Moon is better known than that of the Earth, for the whole of its surface has been mapped and delineated with great accuracy and precision. The Moon is in no sense a duplicate of its primary, and no analogy exists between the Earth and her satellite. Evidence is wanting of the existence of an atmosphere surrounding the Moon; no clouds or exhalations can be perceived, and no water is believed to exist on the lunar surface. Consequently there are no oceans, seas, rivers, or lakes; no fertile plains or forest-clad mountains, such as are found upon the Earth. Indeed, all the conditions essential for the support and maintenance of organic life by which we are surrounded appear to be nonexistent on the Moon. Our satellite has no seasons; its axial rotation is so slow that one lunar day is equal in length to fourteen of our days; this period of sunshine is succeeded by a night of similar duration. The alternation of such lengthened days and nights subjects the lunar surface to great extremes of heat and cold.

When viewed with a telescope, the surface of the Moon is perceived to consist of lofty mountain chains with rugged peaks, numerous extinct volcanoes called crater mountains, hills, clefts, chasms, valleys, and level plains--a region of desolation, presenting to our gaze the shattered and upturned fragments of the Moon's crust, convulsed by forces of a volcanic nature which have long since expended their energies and died out. The mountain ranges on the Moon resemble those of the Earth, but they have a more rugged outline, and their peaks are more precipitous, some of them rising to a height of 20,000 feet. They are called the Lunar Alps, Apennines, and Cordilleras, and embrace every variety of hill, cliff, mound, and ridge of comparatively low elevation. The plains are large level areas, which are situated on various parts of the lunar surface; they are of a darker hue than the mountainous regions by which they are surrounded, and were at one time believed to be seas. They are analogous to the prairies, steppes, and deserts of the Earth.

_Valleys._--Some of these are of spacious dimensions; others are narrow, and contract into gorges and chasms. Clefts or rills are long cracks or fissures of considerable depth, which extend sometimes for hundreds of miles across the various strata of which the Moon's crust is composed.

The characteristic features of the Moon's surface are the crater mountains: they are very numerous on certain portions of the lunar disc, and give the Moon the freckled appearance which it presents in the telescope, and which Galileo likened to the eyes in the feathers of a peacock's tail. They are believed to be of volcanic origin, and have been classified as follows: 'Walled plains, mountain rings, ring plains, crater plains, craters, craterlets, and crater cones.' Upwards of 13,000 of these mountains have been enumerated, and 1,000 are known to have a diameter exceeding nine miles. Walled plains consist of circular areas which have a width varying from 150 miles to a few hundred yards. They are enclosed by rocky ramparts, whilst the centre is occupied by an elevated peak. The depth of these formations, which are often far below the level of the Moon's surface, ranges from 10,000 to 20,000 feet. Mountain rings, ring plains, and crater plains resemble those already described, but are on a smaller scale; the floors of the larger ones are frequently occupied by craters and craterlets. The latter exist in large numbers, and some portions of the Moon's surface appear honeycombed with them, the smaller craters resting on the sides of larger ones and occupying the bottoms of the more extensive areas. There is no kind of formation on the Earth's surface that can be compared with these crater mountains, which indicate that the Moon was at one time a fiery globe convulsed by internal forces which found an outlet in the numerous volcanoes scattered over her surface.

The most remarkable of these volcanic mountains have been named after distinguished men. (1) Copernicus is one of the most imposing; its crater is 56 miles in diameter, and situated at its centre is a mountain with six peaks 2,400 feet in height. The ring by which it is surrounded rises 11,000 feet above the floor of the crater, and consists of terraces believed to have been created by the partial congelation and periodic subsidence of a lake of molten lava which occupied the enclosed area.

(2) Tycho is one of the most magnificent and perfect of lunar volcanoes, and is also remarkable as being a centre from which, when the Moon is full, there radiates a number of bright streaks which extend across the lunar surface, over mountain and valley, through ring and crater, for many hundreds of miles. Their nature is unknown, and nothing resembling them is found on the Earth. Tycho has a diameter of 50 miles and a depth of 17,000 feet. The peak which rises from the floor of the crater attains a height of 6,000 feet, and the rampart consists of a series of terraces which give variety to the appearance of the inner wall. The surface of the Moon round Tycho is honeycombed with small volcanoes.

(3) Clavius is one of the most extensive of the walled plains; it has a diameter of 142 miles and an area of 16,500 square miles. The rocky annulus which surrounds it is very lofty and precipitous, and at one point reaches a height of 17,300 feet. Upwards of 90 craters have been counted within this space, one of the peaks attaining to an elevation of 24,000 feet above the level floor of the plain. It is believed that the lowest depths of this wild and precipitous region are never penetrated by sunlight, they are so overshadowed by towering crag and fell which intercept the solar rays; and, as there is no atmosphere to cause reflection, they are consequently enveloped in perpetual darkness.

(4) Plato has a diameter of about 60 miles and an area of 2,700 square miles; its central peak rises to a height of 7,300 feet. It has an irregular rampart which is broken up into terraces averaging about 4,000 feet high; three cones, each with an elevation of from 7,000 to 9,000 feet, rest on its western border.

(5) Theophilus is the deepest of the visible craters on the Moon. It has a diameter of 64 miles, and the inner edge of the ring rises from the level floor to a height ranging from 14,000 to 18,000 feet. A group of mountains occupies the centre of the area, the highest peak of which reaches an elevation of 5,200 feet. Cyrillus and Catharina, two adjacent craters, are each about 16,000 feet deep and connected by a wide valley.

(6) Aristarchus is the brightest spot on the Moon, and appears almost dazzling in the telescope. The crater has a diameter of 42 miles, the centre of which is occupied by a steep mountain. The rampart on the western side rises to a height of 7,500 feet, on the east it becomes a plateau which connects it with a smaller crater called Herodotus. Bright streaks radiate from Aristarchus when there is full moon, and extend for a considerable distance over the surface of the orb.

Though the face of the Moon has been carefully scanned for two centuries and a half, and selenographers have mapped and delineated her features with the utmost accuracy and precision, yet no perceptible change of a reliable character has been perceived to occur on any part of the orb. The surface of the hemisphere directed towards the Earth appears to be an alternation of desert plains, craggy wildernesses, and extinct volcanoes--a region of desolation unoccupied by any living thing, and 'upon which the light of life has never dawned.' Owing to the absence of an atmosphere, there is neither diffuse daylight nor twilight on the Moon. Every portion of the lunar surface not exposed to the Sun's rays is shrouded in darkness, and black shadows can be observed fringing prominences of silvery whiteness. If the Moon were enveloped in an atmosphere similar to that which surrounds the Earth, the reflection and diffusion of light among the minute particles of watery vapour which permeate it would give rise to a gradual transition from light to darkness; the lunar surface would be visible when not illumined by the direct rays of the Sun, and before sunrise and after sunset, dawn and twilight would occur as upon the Earth. But upon the Moon there is no dawn, and the darkness of night envelops the orb until the appearance of the edge of the Sun's disc above the horizon, then his dazzling rays illumine the summits and loftiest peaks of the lunar mountains whilst yet their sides and bases are wrapped in deep gloom. Since the pace of the Sun across the lunar heavens is 28 times slower than it is with us, there is continuous sunshine on the Moon for 304 hours, and this long day--equal to about a fortnight of our time--is succeeded by a night of similar duration. As there is no atmosphere overhead to diffuse or reflect the light, the Sun shines in a pitch-black sky, and at lunar noonday the planets and constellations can be seen displaying a brilliancy of greater intensity than can be perceived on Earth during the darkest night. Every portion of the Moon's surface is bleak, bare, and untouched by any softening influences. No gentle gale ever sweeps down her valleys or disturbs the dead calm that hangs over this world; no cloud ever tempers the fierce glare of the Sun that pours down his unmitigated rays from a sky of inky blackness; no refreshing shower ever falls upon her arid mountains and plains; no sound ever breaks the profound stillness that reigns over this realm of solitude and desolation.

As might be expected, Milton makes frequent allusion to the Moon in 'Paradise Lost,' and does not fail to set forth the distinctive charms associated with the unrivalled queen of the firmament. The majority of poets would most likely regard a description of evening as incomplete without an allusion to the Moon. Milton has adhered to this sentiment, as may be perceived in the following lines:--

till the Moon,
Rising in clouded majesty, at length
Apparent queen, unveiled her peerless light,
And o'er the dark her silver mantle threw.--iv. 606-609.

now reigns
Full-orbed the Moon, and with more pleasing light,
Shadowy sets off the face of things.--v. 41-43.

The association of the Moon with the nocturnal revels and dances of elves and fairies is felicitously expressed in the following passage:--

or faery elves,
Whose midnight revels, by a forest side
Or fountain, some belated peasant sees,
Or dreams he sees, while overhead the Moon
Sits arbitress, and nearer to the Earth
Wheels her pale course.--i. 781-86.

In contrast with this, we have Milton's description of the Moon when affected by the demoniacal practices of the 'night-hag' who was believed to destroy infants for the sake of drinking their blood, and applying their mangled limbs to the purposes of incantation. The legend is of Scandinavian origin and the locality Lapland:--

Nor uglier follow the night-hag, when called
In secret, riding through the air she comes,
Lured with the smell of infant blood, to dance
With Lapland witches, while the labouring Moon
Eclipses at their charms.--ii. 662-66.

In his description of the massive shield carried by Satan, the poet compares it with the full moon:--

his ponderous shield
Ethereal temper, massy, large, and round,
Behind him cast. The broad circumference
Hung on his shoulders like the Moon.--i. 284-87.

The phases displayed by the Moon in her monthly journey round the Earth, and which lend a variety of charm to the appearances presented by the orb, are poetically described by Milton in the following lines:--

but there the neighbouring Moon
(So call that opposite fair star) her aid
Timely interposes, and her monthly round
Still ending, still renewing, through mid-Heaven
With borrowed light her countenance triform
Hence fills and empties, to enlighten the Earth,
And in her pale dominion checks the night.--iii. 726-32.

It is interesting to observe how aptly Milton describes the subdued illumination of the Moon's reflected light, as compared with the brilliant radiance of the blazing Sun, and how the distinguishing glory peculiar to each orb is appropriately set forth in the various passages in which they are described; their contrasted splendour enhancing rather than detracting from the grandeur and beauty belonging to each.

THE PLANET EARTH[14]

No lovelier planet circles round the Sun than the planet Earth, with her oceans and continents, her mountains, valleys, rivers, lakes, and plains; surrounded by heaven's azure, radiant with the sunlight of her day and adorned by night with countless sparkling points of gold. This beautiful world, the abode of MAN, is of paramount importance to us, and is the only part of the universe of which we have any direct knowledge.

The Earth may be regarded as one of the Sun's numerous family, and is situated third in order from the refulgent orb, round which it revolves in an elliptical orbit at a mean distance of 92,800,000 miles. The Earth is nearest to the Sun at the end of December, and furthest away at the beginning of July; the difference between those distances is 3,250,000 miles--the extent of the eccentricity of the planet's orbit. The figure of the Earth is that of an oblate spheroid; it is slightly flattened at the poles and bulges at the equator. Its polar or shortest diameter is 7,899 miles, its equatorial diameter is 7,926 miles--greater than the other by 27 miles. The circumference of the Earth at the equator is 24,899 miles, and the total area of its surface is 197,000,000 square miles. Its mean density is 5-1/2 times greater than that of water.

The two principal motions performed by the Earth are: (1) Rotation on its axis; (2) its annual revolution round the Sun. The Earth always rotates in the same manner, and in the same direction, from west to east. As the axis of rotation corresponds with the shortest diameter of the planet, it affords strong evidence that the Earth assumed its present shape whilst rapidly rotating round its axis when in a fluid or plastic condition. This would accord with the nebular hypothesis. The ends of the Earth's axis are called the poles of the Earth; one is the north, the other the south pole. The north pole is directed towards a star in the Lesser Bear called the Pole Star. The south pole is directed to a corresponding opposite part of the heavens. The Earth's axis is inclined 63 deg. 33' to the plane of the ecliptic, and is always directed to the same point in the heavens. The Earth accomplishes a revolution on its axis in 23 hours 56 minutes 4 seconds mean solar time, which is the length of the sidereal day. This rate of rotation is invariable. At the equator, where the circumference of the globe exceeds 24,000 miles, the velocity of a point on its surface is upwards of 1,000 miles an hour, but, as the poles are approached, the tangential velocity diminishes, and at those points it is entirely absent. The Earth accomplishes a revolution of her orbit in 365 days 6 hours 9 minutes; in her journey round the Sun she travels a circuit of 580,000,000 miles at an average pace of 66,000 miles an hour. The Earth has other slight motions called _perturbations_, which are produced by the gravitational attraction of other members of the solar system. The most important of these is Precession of the Equinoxes, which is caused by the attraction of the Sun, Moon, and planets, on the protuberant equatorial region of the globe. This attraction has a tendency to turn the Earth's axis at right angles to her orbit, but it only results in the slow rotation of the pole of the equator round that of the ecliptic, which is occurring at the rate of 1 deg. in 70 years, and will require a period of 25,868 years to complete an entire revolution of the heavens.

The spot on Earth round which is centred the chief interest in Milton's poem is Paradise, which was situated in the east of Eden, a district of Central Asia. It was here where God ordained that man should first dwell--a place created for his enjoyment and delight. Satan, after his soliloquy on Mount Niphates, directs his way to Paradise, and arrives first in Eden, where he beholds from a distance the Happy Garden--

So on he fares, and to the border comes
Of Eden, where delicious Paradise,
Now nearer, crowns with her enclosure green,
As with a rural mound, the champain head
Of a steep wilderness, whose hairy sides
With thicket overgrown, grotesque and wild,
Access denied; and overhead upgrew
Insuperable highth of loftiest shade,
Cedar, and pine, and fir, and branching palm,
A sylvan scene, and, as the ranks ascend,
Shade above shade, a woody theatre
Of stateliest view. Yet higher than their tops
The verdurous wall of Paradise up-sprung;
Which to our general sire gave prospect large
Into his nether empire neighbouring round.
And higher than that wall, a circling row
Of goodliest trees, loaden with fairest fruit,
Blossoms and fruits at once of golden hue,
Appeared, with gay enamelled colours mixed;
On which the Sun more glad impressed his beams
Than in fair evening cloud, or humid bow,
When God hath showered the Earth: so lovely seemed
That landskip. And of pure now purer air
Meets his approach, and to the heart inspires
Vernal delight and joy, able to drive
All sadness but despair. Now gentle gales,
Fanning their odoriferous wings, dispense
Native perfumes, and whisper whence they stole
Those balmy spoils.--iv. 131-59.

Satan, having gained admission to the Garden by overleaping the tangled thicket of shrubs and bushes which formed an impenetrable barrier and prevented any access to the enclosure within, he flew up on to the Tree of Life--

Beneath him, with new wonder, now he views,
To all delight of human sense exposed,
In narrow room Nature's whole wealth; yea, more!--
A Heaven on Earth: for blissful Paradise
Of God the garden was, by Him in the east
Of Eden planted, Eden stretched her line
From Auran eastward to the royal towers
Of great Seleucia, built by Grecian kings,
Or where the sons of Eden long before
Dwelt in Telassar. In this pleasant soil
His far more pleasant garden God ordained.
Out of the fertile ground he caused to grow
All trees of noblest kind for sight, smell, taste;
And all amid them stood the Tree of Life,
High eminent, blooming ambrosial fruit
Of vegetable gold; and next to life,
Our death, the Tree of Knowledge, grew fast by--
Knowledge of good, bought dear by knowing ill.
Southward through Eden went a river large,
Nor changed his course, but through the shaggy hill
Passed underneath ingulfed; for God had thrown
That mountain, as his garden mould, high raised
Upon the rapid current, which, through veins
Of porous earth with kindly thirst up-drawn,
Rose a fresh fountain, and with many a rill
Watered the garden; thence united fell
Down the steep glade, and met the nether flood,
Which from his darksome passage now appears,
And now, divided into four main streams,
Runs diverse, wandering many a famous realm
And country whereof here needs no account;
But rather to tell how, if Art could tell
How, from that sapphire fount the crisped brooks,
Boiling on orient-pearl and sands of gold,
With mazy error under pendent shades
Ran nectar, visiting each plant, and fed
Flowers worthy of Paradise, which not nice Art
In beds and curious knots, but Nature boon
Poured forth profuse on hill, and dale, and plain,
Both where the morning Sun first warmly smote
The open field, and where the unpierced shade
Imbrowned the noontide bowers.--iv. 205-46.

Milton's description of Paradise is not less remarkable in its way than the lurid scenes depicted by him in Pandemonium. The versatility of his poetic genius is nowhere more apparent than in the charming pastoral verse contained in this part of his poem. The poet has lavished the whole wealth of his luxuriant imagination in his description of Eden and blissful Paradise with its 'vernal airs' and 'gentle gales,' its verdant meads, and murmuring streams, 'rolling on orient-pearl and sands of gold;' its stately trees laden with blossom and fruit; its spicy groves and shady bowers, over which there breathed the eternal Spring.

In Book IX. Satan expresses himself in an eloquent apostrophe to the primitive Earth, over which he previously wandered for seven days--

O Earth, how like to Heaven, if not preferred
More justly, seat worthier of gods, as built
With second thoughts, reforming what was old!
For what God, after better, worse would build?
Terrestrial Heaven, danced round by other Heavens,
That shine, yet bear their bright officious lamps,
Light above light, for thee alone, as seems,
In thee concentring all their precious beams
Of sacred influence! As God in Heaven
Is centre, yet extends to all, so thou
Centring receiv'st from all those orbs; in thee,
Not in themselves, all their known virtue appears,
Productive in herb, plant, and nobler birth
Of creatures animate with gradual life
Of growth, sense, reason, all summed up in Man,
With what delight I could have walked thee round,
If I could joy in aught--sweet interchange
Of hill and valley, rivers, woods, and plains,
Now land, now sea, and shores with forest crowned,
Rocks, dens, and caves.--ix. 99-118.

Though it is impossible to regard the Earth as possessing the importance ascribed to it by the ancient Ptolemaists; nevertheless, our globe is a great and mighty world, and appears to be one of the most favourably situated of all the planets, being neither near the Sun nor yet very far distant from the orb; and although, when compared with the universe, it is no more than a leaf on a tree in the midst of a vast forest; still, it is not the least important among other circling worlds, and unfailingly fulfils the part allotted to it in the great scheme of creation.

THE PLANET HESPERUS

This is the beautiful morning and evening star, the peerless planet that ushers in the twilight and the dawn, the harbinger of day and unrivalled queen of the evening. Venus, called after the Roman goddess of Love, and also identified with the Greek Aphrodite of ideal beauty, is the name by which the planet is popularly known; but Milton does not so designate it, and the name 'Venus' is not found in 'Paradise Lost.' The ancients called it Lucifer and Phosphor when it shone as a morning star before sunrise, and Hesperus and Vesper when it became visible after sunset. It is the most lustrous of all the planets, and at times its brilliancy is so marked as to throw a distinct shadow at night.

Venus is the second planet in order from the Sun. Its orbit lies between that of Mercury and the Earth, and in form approaches nearer to a circle than that of any of the other planets. It travels round the Sun in 224.7 days, at a mean distance of 67,000,000 miles, and with an average velocity of 80,000 miles an hour. Its period of rotation is unknown. By the observation of dusky spots on its surface, it has been surmised that the planet completes a revolution on its axis in 23-1/4 hours; but other observers doubt this and are inclined to believe that it always presents the same face to the Sun. When at inferior conjunction Venus approaches nearer to the Earth than any other planet, its distance then being 27,000,000 miles. Its greatest elongation varies from 45 deg. to 47 deg. 12'; it therefore can never be much more than three hours above the horizon before sunrise, or after sunset. Venus is a morning star when passing from inferior to superior conjunction, and during the other half of its synodical period it is an evening star. The planet attains its greatest brilliancy at an elongation 40 deg. west or east of the Sun--five weeks before and after inferior conjunction. It is at these periods, when at its greatest brilliancy, that it casts a shadow at night.

Though so pleasing an object to the unaided eye, Venus, when observed with the telescope, is often a source of disappointment--this is on account of its dazzling brilliancy, which renders any accurate definition of its surface impossible. Sir John Herschel writes: 'The intense lustre of its illuminated part dazzles the sight, and exaggerates every imperfection of the telescope; yet we see clearly that its surface is not mottled over with permanent spots like the Moon; we notice in it neither mountains nor shadows, but a uniform brightness, in which sometimes we may indeed fancy, or perhaps more than fancy, brighter or obscurer portions, but can seldom or never rest fully satisfied of the fact.' It is believed that the surface of the planet is invisible on account of the existence of a cloud-laden atmosphere by which it is enveloped, and which may serve as a protection against the intense glare of the sunshine and heat poured down by the not far-distant Sun. Schroeter, a German astronomer, believed that he saw lofty mountains on the surface of the planet, but their existence has not been confirmed by any other observer. The Sun if viewed from Venus would have a diameter nearly half as large again as when seen from the Earth; it is therefore probable that the planet is subjected to a much higher temperature than what is experienced on our globe.

The phases of Venus are similar to those exhibited by the Moon, and are caused by a change in position of the illumined hemisphere of the planet with regard to the Earth. At superior conjunction the whole enlightened disc of the planet is turned towards the Earth, but is invisible by being lost in the Sun's rays. Shortly before or after it arrives at this point, its form is gibbous, the illumined portion being less than a circle but greater than a semi-circle. At its greatest elongation west or east of the Sun the planet resembles the Moon in quadrature--a half moon--and between those points and inferior conjunction it is visible as a beautiful crescent. It becomes narrower and sharper as it approaches inferior conjunction, until it resembles a curved luminous thread prior to its disappearance at the conjunction. After having passed this point it reappears on the other side of the Sun as the morning star.

It would be only natural to imagine that this peerless orb, the most beautiful and lustrous of the planets, upon which men have gazed with longing admiration, and designated the emblem of 'all beauty and all love,' should have impressed Milton's poetical imagination with its charming appearance, and stimulated the flow of his captivating muse. He addresses the orb as

Fairest of Stars, last in the train of night,
If better thou belong not to the dawn,
Sure pledge of day, that crown'st the smiling morn
With thy bright circlet, praise Him in thy sphere
While day arises, that sweet hour of prime.--v. 166-70.

In these lines the poet alludes to Venus as the morning star.

In the other passages in his poem Milton associates the planet sometimes with the morning and at other times with the evening--

His countenance, as the Morning Star that guides
The starry flock.--v. 708-709.

Or if the Star of Evening and the Moon
Haste to thy audience, Night with her will bring
Silence, and Sleep listening to thee will watch.--vii. 104-106.

And hence the morning planet gilds her horns.--vii. 366.

The Sun was sunk and after him the Star
Of Hesperus, whose office is to bring
Twilight upon the Earth, short arbiter
Twixt day and night.--ix. 47-50.