*Vere rem reputanti, philosophia naturalis, post verbum Dei, certissima superstitionis medicina est; eademque probatissimum fidei alimentum.
i Itaque merito; religioni donatur tanquam fidissima ancilla: cum altera voluntatem Dei, altera potestatem manifestet.'
BACONI NOV. Org. Aph. LXXXIX.
OUR SATELLITE.
tlfttijgrajijjg
For the convenience of those who may wish to possess the large Photographed Maps of the Moon, referred to in the Index, in the combined shape of large chart-maps of the whole surface, it is proposed to issue them in this form also in the course of publication of the work. Particulars as to price, &c, of this additional publication will be duly announced.
FIRST NUMBER.
Lwm
6. LESPIAULTl ir»tt*atq«JLONDON:
A. W. BENNETT, 5 BISHOPS G AT E STREET WITHOUT.
1862.
IS
V
■a.
The right of translation is reserved.
OUR SATELLITE.
rihtflgrajijjg
ACCORDING TO THE PRESENT STATE OF SCIENCE.
BY
DR. A. LE VENGEIJR-D'ORSAN.
FIRST NUMBER.
LBOS
6. LESPIAULTj
LONDON:
A. W. BENNETT, 5 BI SHOPSGATE STREET WITHOUT.
1862.
The right of translation is reserved.
LONDON
PRINTED BY SPOTTISWOODE AND CO.
NEW-STREET SQUARE
THE RIGHT HON. HENRY LORD BROUGHAM AND VAUX,
&c. &c. &c.
AS A TESTIMONY OF THE HIGHEST ADMIRATION AND ESTEEM,
AND AS A SINCEEE TOKEN OF RESPECT
FOR HIS LORDSHIP'S EMINENT SERVICES IN THE CAUSE OF SCIENCE,
THIS WORK IS INSCRIBED BY
THE AUTHOR.
!
DIVISION I.
Preface.
General Introduction.
The Moon (General Remarks).
Topography of the Lunar Surface.
General Remarks.
Photographs of the same spots and regions taken at different periods of lunation, and representing them under different degrees of illumination, and, consequently, different appearances.
Descriptions, accompanied with Photographed Maps in outline, and traced with parallels of Latitude and Longitude, expla- natory of the preceding Photographs.
Tycho and surrounding country at different periods of lunation,
&c. &c.
Large additional Photographs of various separate spots, drawings, and descriptive letterpress.
Large Photographed Maps of the whole of the illuminated surface visible during the different phases.
Different Stereoscopic Views.
vm INDEX.
DIVISION II.
General Mathematical Selenography.
General Physical Selenography.
General Concluding Remarks.
APPENDIX.
ADDENDA.
FOR the appearance of this work the scientific world will require no apology. It is the fruit of continued daily and nightly labours, undertaken with no prospect of pecuniary reward, per- severed in solely from love of the undertaking and the cause of science, and which can only be appreciated by those who have devoted themselves to similar pursuits. Many times I have felt them to press heavily on my health; but the strong interest with which Our Satellite has always inspired me, sus- tained and supplied me with the strength necessary for the prosecution of my task.
I have accumulated a large mass of material, and shall continue constantly to add to it, and keep it so prepared that the publication can go on without interruption. It was only after the most careful consideration that I resolved to send forth into the world this result of my labours, and after the most diligent enquiries whether some other and abler fellow- worker might not have produced, or contemplated the production
PREFACE.
of, a similar work. If I had found such to be the case, I would have assisted him (as I have often so expressed myself) with my material, and an experience now grown familiar with the lunar surface.
All my enquiries, however, have had but one result, viz.—
that no similar work is yet in existence, nor, as far as my enquiries extend, in contemplation.
If we take a retrospective view of Selenographic labours for the last two centuries, — (for previously to the invention of the telescope, 1609, there could have been no real study of the moon's surface) — we can do little more than name the vene- rable Galileo, and enumerate some works bearing on the subject from the hands of a few eminent men. The productions of Hevel, Tobias Mayer, and Schroter, hold a prominent place;
those, too, of poor indefatigable Lohrmann, whom, when almost deprived of sight, death surprised in the midst of his valuable labours; those also of W. Beer and Dr. Madler, to whose persevering industry we are indebted for the best lunar map extant.*
All this, however, proves how slowly, though surely, the spark of science spreads, and that though each successive worker builds on the experience of his predecessors, the super- structure advances almost imperceptibly, whilst yet fresh energy
* A list of the works on lunar science, al- ready published and referred to in the course
of this work, will be found in a part of the Appendix.
is at each step infused into new explorers, and a new stimulus given them, to add the fruits of their labours also to the stores already accumulated. No doubt if these men had had the experience and means of observation which science, within the last quarter of a century, may be said almost to have created, they would have accomplished what I have set myself to perform; but in the interval that has elapsed since the last writers of eminence, Dr. Madler and W. Beer, published their lunar map (now some twenty-four years ago), Photography has been developed, and mechanical aids, telescopic and other, have been so improved, that difficulties, hitherto insurmountable, in giving a portraiture of the moon's surface, can now be over- come by skill and perseverance.
Detail being my principal object, large photographs of various separate spots are given, in addition to those which, taken at different periods of lunation, contain at once many spots and regions, and represent them under different aspects.
From the guidance and instruction these afford, together with the fact of their presenting one and the same spot under various degrees of illumination, and consequently diverse appear- ances, elaborate drawings founded on many years' observations and measurements will be given, exhibiting approximately the real outline of each respective spot. Those photographs of the various lunar parts that have been taken at one and the same period of lunation, may also be joined together, and thus correct
11
PREFACE.
maps are given of the several phases. There is, in addition, one photographed general map of the full moon, and also several stereoscopic views.
The photographs are all on a scale never before executed, probably never before attempted, as they were only completed by peculiar mechanical contrivances and instruments, and, above all, after a great expenditure of time and after many trials. With respect to the numerous drawings of lunar objects interspersed throughout the work, I was from the beginning convinced, that he who attempts to give such correctly, must possess a knowledge of the laws of perspective and shadow, and be able to give proper attention to the direction of the incident and reflected light.
I have, therefore, devoted myself to these studies; and the experience I have thus acquired has been of great assistance in perfecting my delineations. The greater portion of the descrip- tions is taken from detailed notes and memoranda, made at the moment the eye was to the telescope, carefully and minutely compared with other means of correction, that have presented themselves during the progress of the work.
From this slight sketch the scientific reader will at once see the direction I have followed, respecting the object I have in view; and considering the time it has required and will yet require, he will perceive that it will be a work taking up the
12
greater part of a life-time. Whether in sending it forth into the world, with a view of aiding the cause of science, I shall have succeeded, as I have endeavoured to do, in extending the knowledge we already possess of Our Satellite, and whether I have in any adequate way met the demands which the pre- sent high state of science most justly makes, others, not I, must judge.
My fellow-workers in the fields of science alone can decide, whether rightly or not I have applied to myself the words :—
CHI NON PUO QUEL CHE VUOL, QUEL CHE PU5 VOGLIA.
A. LE VENGEUK-D'OESAN.
July 1862.
13 D
Survey this midnight scene:
What are earth's kingdoms to yon boundless orbs, Of human souls, one day, the destined range!
WHO can look upwards to the heavens on a starry night, and not feel moved at the wonders which he there beholds! And who can reflect that those lucid points which he sees scattered over their surface, are not lights set there merely to illumine the solitudes of space, or fill its voids, but that they are mighty worlds, sweeping along, with solemn regularity, through trackless immensity, under the control of undeviating laws; — that (as all analogy goes to prove) they may be tenanted by various ranks of animated beings,— that all are maintained in changeless order, harmony and movement, by the Creator's eternal fiat; —what mind capable of these reflections, but must be filled with a deep sense of mystery and awe ! The unassisted eye sees in the nocturnal heavens nothing beyond points of light;
and, whilst uninformed by science, believes them to be what they appear; but that many of them are masses of enormous magnitude is plain from the consideration, that unless they were such, they would be invisible to us, so vast is the distance at
15
INTRODUCTION.
which they are placed. The distance of even the nearest of those stars which are situated beyond the limits of our planetary
system, is absolutely inconceivable. It may be stated in numbers, it may be illustrated by examples, but it cannot be compre- hended ; it cannot even be imagined. The mind is utterly impotent to grasp such distances, and yet they are demonstrable by the most rigid deductions of science. They prove beyond the smallest doubt the vast magnitudes of those stars. They prove also that they are self-luminous; for no reflected light could travel over the measureless tracts of space, which separate us from them, without being absorbed or dispersed before rendering them visible to us. They are seen by us, not because they reflect light, but because they shine of themselves; because, in a word, they are SOLAR STARS, each the centre of a system of his own, and from sources of his own, sending light to the most distant regions accessible to his rays.
If the unassisted eye discover such wonders, what astonish- ment must fill the observer when the telescope penetrates into space, and lifting the veil of distance, multiplies thousands to millions, displaying worlds after worlds in countless hosts rolling through immensity, apparently in inextricable confusion, but in reality in undeviating order, and each single one as perfect as our own. What mind capable of adequately realising such facts, but must, whilst doing so, be filled with the sublimest re- flections. We perceive that this earth is a mere shred,— the annihilation of which would leave creation as vast and as entire as before,— that though it were to disappear, there are other worlds which roll afar,— where God's physical and moral laws rule undisturbed, — where the ties of neighbourhood and
1G
home may be known — where piety may have its temples and God His worshippers.
But further, multitudinous as are the worlds and immeasurable as is the distance which the telescope reveals to us, yet even with its aid we see but a fragment of creation; systems after systems still throng beyond, in the unsearchable heights of heaven;
for who can question it? What is seen is nothing to what is unseen, for what is seen is limited by the range of our instruments; what is unseen has no limit ; and though all that the eye of man can take in, or his fancy can grasp, were swept away, there might still remain as ample a field as ever, which the Deity may have peopled with innumerable worlds. The more recent observations of Astronomy make this highly probable;
the discovery of the Nebulse opens up limitless fields for astonish- ment and speculation. It carries us up another step in the ascending scale of immensity, and makes it impossible for us even to conjecture where progression is to end.
The Nebulae have opened vast fields for the sublimest specu- lations of Astronomy. Anterior to their discovery the universe might appear to have been composed of an indefinite number of suns, uniformly scattered over space, and each encompassed by such a planetary attendance as takes place in our own system;
but now we recognise not merely suns, but SYSTEMS OF SUNS, grouped into clusters in sublime arrangement, countless in number and vastly separated in space, the whole probably revolving round some mysterious centre !
Incomparably beyond all other sciences, Astronomy impresses us with a sense of Omnipotent Power and Wisdom. And whilst
17 E
INTRODUCTION.
we bear in mind that He who presides over all worlds is mindful of man, that the Being whose eye is abroad over all the universe, is He who gives vegetation to every blade of grass and life to every animated thing — whilst we bear this in mind, and humbly bow before this combination of infinite power and wisdom, we must at the same time be elevated by the thought that insig- nificant as we may seem, from our species and position, He yet has endowed us with the high faculty of investigating His works, and learning, through the sublime medium of reason, the lessons they are designed to teach.
Science is not of spontaneous growth. It is the child of time, nurtured in the lapse of ages. Feeble in its infancy, and often cradled in error, it is only by incessant culture that it slowly reaches maturity. This is strikingly illustrated by the history of Astronomy.
If we reflect on the vast discoveries made in recent times, and then turn back to the era of primitive observation, and from thence trace down through successive generations the gradual expansion of the science, we cannot fail to be astonished at the contrast presented by its feeble infancy and its colossal growth.
Astronomy has its origin in the profoundest depths of our nature. Other sciences have their origin in man's physical requirements, Astronomy in his spiritual. The cravings of the intellect, or the wants of the body, have produced all other sciences, but in Astronomy the first impulse came from the necessities of the soul.
If we search down into the constitution of our being, till we come to the lowest deep of all, we shall find underlying
18
all other wants, a craving for the infinite, a something that desires perfection, a wish that nothing but the thought of what is eternal can satisfy. Nowhere was this want so called into consciousness as beneath the mighty skies of the East.
There the nights are still and cloudless, and many a wise man in the earlier days, full of deep thoughts, ' went out into the fields,' like Isaac, ' to meditate at eventide.' And then those vast plains all solitude, and those mighty skies all stillness, bringing up before the eye and the mind all that is boundless in space and illimitable in time; — around, silence profound as death, above, motion going on for ever; no wonder if men looked upwards to the heavens and deemed that an eternal destiny was enthroned there; that they found in the stars objects for their adoration, and were ' given up to worship the hosts of heaven.'
Astronomy was the religion of the world's youth.
Perverted and astray as this spirit was, still it was re- verential; the true student-ardour animated it. Few in our times have imbibed what was good, though they have been rescued from that which was evil, in it. Eeverence does not characterise the pursuit of science in our time. A mean demand for utility has superseded it; and men now pursue, and listen to discoveries of truth, with scarcely any other feeling than that which a sense of the profit springing from them begets. There is a spirit abroad which seeks for wisdom simply as a means to an end, and that often a mean one;
and this is the spirit rebuked by the ancient and nobler reverence of primitive times — the desire of knowledge for its own sake — truth pursued for the sake of truth — labour and
19
INTRODUCTION.
thought and energy given for no personal gain nor profit; this was the spirit in which, in times of old, men read the aspect of the heavens.
But reverence however deep, the true student-spirit however strong, cannot save men from the errors which seem ever to attend first efforts. The early astronomical observers were no exception; they could not distinguish between what was real and what was apparent. The first and abiding impression made upon them was, that everything visible in the heavens — sun, moon, and stars — was in motion; that the earth alone was at rest, and the centre round which all the others revolved.
To free the mind from this illusion, to distinguish real from apparent motion, was the first great step to be taken in advance; and until it was made, little in reality could be done beyond observing and recording phenomena, out of which, sub- sequently, a true astronomical theory was to be educed, and the false and popular one refuted.
Setting aside some few scattered passages and allusions in ancient authors,* there is no evidence of any kind that the true theory of the earth's motion was apprehended before the beginning of the sixteenth century.
Copernicus was the first to detect the errors of the Ptole- maic system, and to assert the earth's orbital motion. He was followed by Tycho Brahe, Keppler, and Galileo.
The era of these great discoverers extends over the six- teenth, and more than the first half of the seventeenth century.
* Vide Appendix.
20
With Copernicus, and his refutation of the Ptolemaic system, the history of modern Astronomy begins.
The observations of Tycho Brahe, though he rejected the Copernican theory, supplied much of the material upon which Keppler built those astonishing calculations which resulted in the discovery of his famous laws; whilst the invention of the telescope, and his own mighty intellect, enabled Galileo to corroborate the whole, and lay the foundation of the super- structure subsequently raised by the glorious genius of Newton.
It is not easy for us to form a correct estimate of the difficulties which the discoverers of the true astronomical theory had to encounter; difficulties arising as well from the ignorance and prejudices of society, as from the nature of their investi- gations and the means of observation at their disposal. The old philosophy had imbedded itself into men's minds; Plato, Aristotle, Ptolemy, were regarded with a reverence almost super- stitious, and the authority of the Papal Church was roused to maintain the popular belief intact, and denounce any deviation from it as heretical. So that when Galileo demonstrated its unsoundness and completed the proof of the Copernican theory, he was flung as a blasphemer into the dungeons of the Inqui- sition. When we read of his sufferings and recantation, we can hardly avoid feeling indignation and regret. But, in judging of the actions of men, we should always bear in mind the circumstances in which they were placed, the current of opinions in their day, and a due sense of human infirmity. The laity in that day, in all matters of science and philosophy, were in- capable of forming a judgement, and the clerical order was paramount. There was no public opinion, save on religious
21 F
INTRODUCTION.
doctrine, nor any means of addressing even such as did exist, except through the medium of formally convened assemblies and set debate; — and any one acquainted with the history of the time must clearly see, that Galileo and his case could have had no prospect of coming within reach of such protection as these afforded. Besides, the Church of Eome was feeling a heavy blow at the hands of Luther and the Reformation, and the Court of Rome was straining every nerve to recover the autho- rity it had lost, or avert the dangers with which it was menaced. It therefore regarded with a jealous eye the slightest appearance of departure from its decisions. Unfortu- nately, the motion of the heavenly bodies was supposed to be a fact delivered in revelation, and was upheld as possessing all the sanctity of an article of belief. Galileo was conse- quently looked upon as a dangerous heretic who ought to be suppressed; whilst he, on the other hand, imbued with much of the sceptical indifference that characterised many of his time, regarded recantation as in a great degree a mere matter of form, a piece of meaningless ceremonial forced upon him by ecclesiastical authority, to be submitted to with the best grace he could command. But, whatever be the palliation adduced, either for the weakness of the philosopher or the intolerance of the priest, the recantation of the one and the cruelty of the other have left a stain on the escutcheons of science and religion, which the champions of both would now gladly efface. But when, after rising from his knees, Galileo, absorbed in the truth he had taught, suddenly muttered to a bystander, tEi pur si muove'*—
' It moves for all that' — he then uttered a truth which all the devices of men could never after succeed in stifling; a truth
* Or, according to others. ' E gira nondimeno.' 22
that will abide as permanent and enduring as the earth itself.
By its enunciation he dragged down the pillars on which the old fabric of error rested for support, and with them the whole cumbrous pile toppled to the ground. A new foundation was laid, solid and immovable, on which a new temple was to rise, to be from thenceforth dedicated to the genius of truth
alone.
We have arrived at the primary elemental fact of the earth's motion, and from the day of its first promulgation until now, Astronomy has continued to advance with rapid strides, adding discovery to discovery, until at the present time it has achieved triumphs transcending in vastness and magnificence those won in all other departments of science put together.
We now know that the sun is a centre of motion, and that round it the vast group of orbs, which constitutes the solar system, moves, sustained by him in space and held by him in perpetual control. But the sun himself, with all his train of planets, moons, comets, and asteroids, is, in his turn, subordinate to a still mightier centre, fixed in space at an immeasurable distance; a distance so vast that the mind is bewildered in the contemplation of the numbers that express it.
Imagine, as the moon revolves round the earth, and the earth round the sun, that the sun in his turn is also bent to an orbit, and that he sweeps round his centre of motion accompanied with all his stupendous train!
From this and other considerations the reflection is forced upon us, that our solar system does not stand alone, that it is neither unique nor insulated, but that it is the type of others
23
INTRODUCTION.
with which it is intimately related. Possibly the number of such systems equals that of the stellar host itself—not merely its front ranks, which alone come within telescopic range; but that, far away, beyond our ken, systems and assemblages still throng innumerable, light from which will never reach our earth.
These are neither conjectures nor imaginations in which science indulges, but sober probabilities, sustained by cautious investigation. Nor can science reject the sublime conception that sun upon sun and system upon system, obedient to one all-pervading law, may wheel round the eternal throne, the last and mightiest centre of the whole !
So much for the speculations of modern Astronomy, but vast and astonishing as they are, they are indefinite and remote;
and absorbing as is their pursuit, they yet cannot have for us the same immediate interest that bodies more within the reach of our examination supply.
The proximity of the moon, the bonds of close and enduring relation in which she is linked to the earth, the influence she exerts upon its surface, and the great importance of the lunar theory, have at all times intently fixed the eye of science on her orb. It is but rational, therefore, that we should feel a strong curiosity to learn as much as is discoverable concerning a world so near and so important to us.
To the examination then of Our Satellite we turn, as the direct and immediate object of our work.
24
GENERAL REMARKS.
THE sublime spectacle which our Satellite presents, as she makes her silent way through the heavens, has, from the earliest times, aroused the wonder of ignorant and challenged the investigation of thoughtful minds; an untiring interest has gathered around her, undiminished as time has advanced, and now, after the lapse of thousands of years, she excites enquiry, which, enlightened as it is by science, is still as eager and as keen as that which drew upwards the first watchings of untutored investigation.
The huge orb on which we stand is one of the group of planetary worlds which circle round the sun; and as it ploughs its way through space, it is constantly attended by its faithful companion, the moon—which, within a mean distance of 238,000 miles, and having a diameter of 2,160, moves continually round it; being made visible to us by the reflected light of the sun, and having a magnitude of ^Vth of that of the earth.
In exactly the same time, also, as she completes her true circuit round the earth, she rotates once upon her axis, presenting always, very nearly, the same hemisphere to us, and, consequently,
25 G
OUR SATELLITE.
keeping the other almost entirely concealed from view. It is only from time to time that small portions of the averted half become visible to us, at the exterior margin, and, remaining exposed for a short interval, again disappear. There thus follows a slight shifting of the central lunar spots, with respect to the moon's equator or first meridian; fresh regions constantly take the outline of the disc, and mountain projections which were prominent one night may have all vanished on the next. This effect is to be ascribed to causes which produce that peculiar apparent swinging of the moon, to and fro, from 6° to 8°, as well in latitude as longitude ; so that during each circuit there occurs an optical dis- placement of the lunar points, a seeming change of place of the spots with respect to the limb — which is termed lunar libration.
The whole area, thus concealed and exposed by turns, amounts to |th of the surface, fths being entirely invisible to us.
In this manner we are able to see, from time to time, more than half of the lunar surface; at one time something more of the eastern and northern, at another time something more of the western or southern margin. We have considered it advisable to state here only what is absolutely necessary, but in a separate part of the work,* we shall fully consider the moon, in her cosmical relations, as a member of the Solar System, investigate the different laws, and explain the various leading points, that belong to a comprehensive survey of lunar science.
Now, however, we shall at once proceed to acquaint the reader with the general physical appearance of Our Satellite, as revealed to us by the aid of the telescope and photography.
* Division II. Mathematical and Physical Selenography.
2G
Notwithstanding the great distance at which she revolves, and other difficulties attending protracted investigation, we are enabled, by persevering observation, to discover that the variety of lunar types of nature is not less than it is upon our earth.
And, notwithstanding their strange mysterious character, the more closely we study them, the more clearly we are enabled to decipher them.
The natural types of Our Satellite necessarily remind us of similar forms on our own globe, and we are involuntarily led to compare them together; but nearly always there exists only some general assimilation in form —
sometimes there is only some very distant point of resemblance, which similarly named lunar and terrestrial objects have in common. It is only after ac- cumulated inferences, carefully drawn, that we are enabled to gain even a partial insight into the structure of lunar forms and their connexion with ter- restrial, and to judge if, and
to what degree, we may be LMMBB^MBBB™™™™™™
justified in transferring ideas of
form and objects, derived from the earth, to appearances on the moon's surface. But we shall, farther on, have occasion to make frequent reference to such comparison — for the present it shall suffice, if the reader, who may not be familiar with astronomical science, should give his attention to the following
27
OUR SATELLITE.
remarks, in order that he may the more clearly understand the different forms which are pourtrayed on our lunar photographs and drawings.
A. The moon, as we have stated, is seen from our globe at the distance of 238,000 miles, and appears to us a plane surface, upon which we see the mountains situ- ated in the centre, as if we were quite vertical to them, but those which are situ- ated towards the margin we see side- ways ; a fact which is explained by the sphericity of her sur- face.
Now, if we were elevated to a great height above our globe, and if we looked down upon its surface, the differ- ent countries, moun- tains, &c, upon it, would present to us an appearance similar to that which those of the moon do now, when we survey her from the earth.
(The accompanying illustrations will suffice to explain.)
28
RELATIVE SIZE AND DISTANCE OF THE EARTH AND MOON.
=3*
IN DIAMETER
MOON -(IN SUPERFICIES IN MAGNITUDE
SECTION OF THE MOON BY
A PLANE THROUGH THE CENTRE ON
A SCALE PROPORTIONAL TO THE 15 INCH
SECTION OF THE EARTH
Y A
3. 67
13.44 V TIMES LESS THAN THE EARTH.
49.25
B. It is quite free from exaggeration to compare the in- equalities on the surface of the earth (arising from mountains, valleys, &c.) with the roughness on the rind of an orange as compared to its mass.
The highest mountain known is Kunchinginga (one of the Himalaya range), which rises to an elevation of 28,178 English feet above the level of the sea, or to about 5£ English miles in perpendicular height; this is the yi^-rd part of the earth's radius, or in round numbers the y^oo^h part of its diameter.
If we suppose a model of our globe to be constructed on a scale of 15 inches in diameter, then the highest mountain would be represented on it by a projection of not more than the yjffth part of an inch, which is not much more than the size of a grain of sand.
The general elevation of continents, or even of any exten- sive tracts of land, does not reach half this proportion; and, therefore, on the model, the whole of the land, with the excep- tion of a few prominent points, will not exceed the thickness of fine paper.
The greatest depth yet reached below the level of the sea is 46,232 English feet; * if this be added to the greatest height above the same level (Kunchinginga, 28,178 feet), we get a distance of 74,410 English feet; this is the ^-^st Part of the earth's radius, and is the greatest known inequality on our globe.
* Appendix, note.
29 n
OUR SATELLITE.
The lunar mountains, &c., &c., are of much greater magni- tude, in proportion to the diameter of the moon, than are those of the earth in relation to its diameter.
C. As the superficies of our globe, and also that of the celestial sphere, are supposed to be divided by a system of circles for the purpose of determining the relative positions and distances of objects upon them, so, in like manner, the moon has a similar system, by which places on her surface are deter- mined with respect to latitude and longitude. The extremities of the axis of rotation are called Poles, and the great circle, equidistant from both, the Equator. Parallel circles (parallels of latitude) are also drawn, similar to those on the earth.
The distance from each Pole to the Equator is 90° (degrees of latitude) : the Northern are marked + (plus, or positive), the Southern — (minus, or negative).
Through a certain point © of the Equator, which forms at a certain period * the centre of the lunar disc, there is drawn the first or principal meridian. As the other half of the moon is not visible to us, degrees of longitude are not counted, as on the earth, from 0° to 360°, but from the first meridian to 90° West, marked + (plus, or positive), in contradistinction to longitude, from the same meridian to 90° East, marked —
(minus, or negative).
Therefore, in the same manner as we are able to deter- mine a place on the earth, or a star in the heavens, so
* Vide Mean Libration. Division II. Mathematical Selenography.
30
we can determine a place or spot on the moon, according to latitude and longitude,— for example :
Determination of the position of the volcano Tycho : —
Long. = Lat. =
— 10° 52' 25"T
— 42° 52' 19 "T
D. But, regarding the points of the lunar compass, it is necessary to bear in mind the following : — They have been fixed, not from their absolute, but from their relative positions
— that is, the several portions of the disc are named in reference to the adjacent quarters of the sky, at the time when the moon is on the meridian. Hence
North is at the top, South is at the bottom; but East and West, as compared with the same points on the terrestrial maps, are reversed, East being to the left, West to the right.
As astronomical telescopes present ob- jects in an inverted position, of course the
North, as seen through them, is at the bottom; the South at the top; the East to the right; the West to the left.
31
OUK SATELLITE.
E. The nomenclature is so arranged, that to the principal lunar objects are affixed the names of distinguished philosophers of present and former times. Some names, especially those of the so-called Maria (Seas), are derived from the influences which were in ancient times generally believed to be exerted by the moon — e.g. Mare Serenitatis; Mare Foecunditatis; Lacus Som- niorum, &c, &c.
Some mountain ranges are named as terrestrial ranges are — e.g. Alps, Apennines, Caucasus, &c, &c.
Each name includes the surrounding adjacent objects. For example, the name alone distinguishes the principal object;
Greek or Boman letters added to it signify, respectively, the elevations or hollows in the vicinity.
This will be seen in the photographed outline maps, which are traced with the parallels of longitude and latitude, and accompany the descriptive letterpress and photographs of each lunar region.
82
The surface of the moon, from pole to pole, is covered with great mountain ranges, and with those extensive dark and dusky patches, the so-called Maria (Seas), which lie deeper than the more illuminated regions that surround them.
Besides the optical changes in form and position which lunar objects undergo, first, through the foreshortenings upon the spherical lunar surface, and, next, from the effects of libration, there are other causes also which affect in a greater degree the appearances of some mountains and whole regions, and seem wholly to metamorphose them for a time.
It is most interesting to examine, during the period of the phases,* the constantly changing and curious forms which objects assume for the first few days after new moon, and
* Our Satellite being an opaque spherical body, shining by virtue of the reflected light of the sun, she can only have that portion of her surface illuminated which is turned, for the time, towards the sun ; and as only that portion of the illuminated disc is seen by us which is turned towards the earth, it follows that, at every change of the moon's position with respect to the earth and sun, we see a different portion of her illuminated surface. As we shall have occasion more fully to explain, in the mathematical part of the work, the moon, on first becoming visible during a lunation, will be seen in the west, soon after sunset, like a thin crescent, with the convex side towards the sun, her horns towards the east.
The crescent begins to fill up, and the illu- minated part to increase, as she advances in her orbit, and at a certain time the jagged and
uneven edge, about the confines of. the illumin- ated part, is changed into nearly a straight line, and the illuminated part turned towards the earth exhibits a semicircle. The line next becomes a curve again, but bending out in a direction dif- ferent from its former inclination, and the moon is said to be gibbous, i.e. bunched or convex.
The curve, turned in a direction from the sun, continues to increase in curvature, and, conse- quently, the breadth of the illuminated portion, until she becomes a circular or full orb.
Now commences a repetition of the same phases, in an inverse order, until at length she appears like a fine thread of light in the morn- ing, a little to the west of the rising sun, and then for a few days, being in conjunction with the sun, she is lost to view. — (Vide Mathematical Selenography.)
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between the last quarter and the change, and it is then that they are seen to great advantage.
These effects have their origin in the varying illumination of the mountains, &c, by the sun.
Twice during each lunation there occurs a period of maximum conspicuousness of each lunar region; this is depen- dent on the altitude of the sun above the respective horizons.
At periods when the sun shines obliquely on the surface of the moon, the elevated parts (mountains, &c, &c.) cast across the adjacent districts dark shadows of a greater or less length, in proportion to their height; by measuring these and allowing for the altitude of the sun above their horizon, the height of most of the mountains has been determined.
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The more obliquely the sun's rays fall upon the mountains,
&c, the longer, of course, will be their shadows.
Sunrise and sunset, in the moon, abound in grand and beautiful effects of light and shade. When day has just broken on any region, and when the sun's rays are flung obliquely upon it — he having but partially risen at the time — the cavities continue still involved in deep shade, and only the tops of the surrounding mountain-ridges are illuminated, and appear as if encircling them with a fringe of gold; whilst now and again, suddenly, the summit of some central peak starts like a star out of the surrounding darkness, having that instant caught the light of the rising sun. As the angle of illumina- tion increases, and the sun rises higher above the lunar horizon, the scene changes and a fresh aspect of things succeeds; day descends along the sides of the loftier summits, and light is diffused among the different cavities. The shadows of the higher mountains grow gradually shorter, rendering lower ranges more distinct, and allowing parts hitherto concealed to come within view; new configurations seem to start into existence, and stand boldly out. But when the sun has reached his greatest altitude, the last shadows disappear, and with them, also, that peculiar sharpness which had previously characterised the different lunar objects; so that it is scarcely possible even for a practised eye to detect and recognise (especially if the sun has reached his maximum altitude), in one and the same region, even well-known forms, which at former periods were easily distinguishable by their colossal proportions.
Nothing can be more perplexing to the unpractised observer than the changes which objects seem to undergo : sometimes
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they appear to be altogether effaced, though previously well-defined;
and at other times, of two which are similar and adjacent, one seems to be wholly unaltered, whilst the other appears to be completely obliterated.
The innumerable hills, small craters, and elevations which surprise the observer, from their multitude, during the period of the phases, either vanish altogether or become scarcely perceptible.
They continue visible as long as they cast shadows, but when they cease to project them, they become indistinguishable, as they do not contrast sufficiently with the parts adjacent, either in brightness or any peculiar hue.
The full moon shows, principally, only differences in light and colour; the great dusky patches (Maria), distinguishable immediately by the naked eye, produce the strongest impression;
and especially noticeable, also, are the radiation systems of bright streaks of light, issuing from different centres, and in widely different proportions, and particularly those
which, exceeding all others in extent, spread themselves from a central spot, called Tycho, in the south-eastern division of the moon, and extend over fully one quarter of her visible hemisphere.
But if we watch some particular region, from night to night, we can perceive the change coming slowly on, till gradually the characteristic colour of the frill moon supervenes, and we can identify the brilliant points and bright streaks which are then predominant, with localities which, at the phases, had presented themselves under wholly different aspects.
3G
We see, from what has been stated, that for some objects—
viz. for minute details and flat regions, or such as are covered only with insignificant hills — in order to observe with precision, we have to select the period of lunar sunset or sunrise for our survey. Any little inequality then assumes importance ; incon- siderable hillocks, small craters, &c, &c, becoming visible in the horizontal light.
For mountainous regions, and for the numerous craters, which the strong shadows cover so much, we can choose as our time of observation the interval between the sun's altitude from 3° to 10°.
In order, therefore, to gain a thorough knowledge of the lunar surface, I consider it necessary to give at first detailed descriptions, photographs and drawings, of particular regions (of course always keeping a coherent representation of the whole in view) ; also to join those photographs of the various lunar parts that have been taken at one and the same period of lunation, and to construct, from their junction, correct maps of the different phases, and then pass on to the study of the large photograph of the full disc of the moon.
I conceive all this to be the more requisite, as we have seen that the moon can never present to us, at the same time, all, or even a considerable portion, of what we are enabled to study through the medium of details.
Let us, therefore, commence with a portion of the SE.
division of the lunar disc — Tycho and the surrounding districts
— the centrum of the most extensive system of streaks of light we know of on the moon.
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The different photographs and drawings are taken and made at different periods of lunation, and give an interesting insight into the extraordinary changes of appearance of one and the same spot.
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with the parallels of longitude and latitude, explanatory of the Photographs (Tycho and the surrounding districts), given here, shall follow in the next number, and at the same time additional Photographs shall appear.
(THE DISTRICTS ADJACENT TO TYCHO.)
( TYCHO AND THE SURROUNDING DISTRICTS .)
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