THE MOOR

New Zealand Illustrated Magazine, 1 August 1901, Page 822

THE MOOR

SECOND AETICLE,

By A. D. Austin, M. Inst., 0.E., F.R.A.S.

IN the article on the Moon, which appeared in the July number of this Magazine, it was stated that with a second article on the Queen of Night,

further photographs would be given, showing greater detail, and that some theories would be advanced as to the formation of the lunar craters, and also the bright lines radiating from Tycho. The first photograph, illustrating this second and concluding article, was taken by Professor Pickering, the well-known and talented astronomer of Harvard College Observatory, and presented by him to the winter. The scale of this view in the original is about forty miles to an inch, bnt is reduce! considerably in order to adapt it to the pages of The Magazine The chain of mountains, crossing the view diagonally, is called the Appennines, and resembles a range of mountains on the earth more than is generally the case. The length of this range is 460 miles. Its south-western side ascends gradually; its opposite side — that towards the circular mountains — breaks down in fearful precipices of immense height, which throw a shadow eighty-three miles long in places on the lunar disc. The highest peak of these mountains is estimated at 21,000 feet. It will be noticed that there are some craters even on this range. Vast masses of the range seem to have fallen away from the cliff, and rest on the plain below. The largest of the circular mountains in our view is Archimedes. The inside of this vast crater is about sixty miles in diameter, and is without the central cone generally

seen. It is, iv fact, a walled plain which appears almost as smooth as a mirror, but is divided into parallel stripes of unequal brightness. The absence of the central cone and the level interior is explained by the theory that molten lava welled up the pipe of the crater, burying the cone, and spread itself out into a horizontal floor. Some of the highest parts of the circular wall are more than 7,000 feet high. The next largest of the craters in the view is Aristillus, thirty-four miles in diameter. It is 11,000 feet deep on its east side, and has a cone in its centre. The third crater is Autolycns, which is nearly as deep as its companion. There are also a number of smaller craters in this view. It may here be mentioned that the highest point on the moon, so far as is known, is in the Leibnitz Mountains. These mountains are occasionally seen as projections on the actual edge of the moon, and rise in one place to an altitude of 41,900 feet above a neighbouring

valley

Our next view is of a region near the centre of the moon's disc, and is inserted chiefly for the purpose of showing the great Cleft of Hyginus. This great crack or furrow on the Moon's surface is some 400 miles in length, and is in places about , one and a-half miles in width, narrowing to half that width or less in other portions of its length. There are large numbers of these olefts or cracks on the lunar surface, but the one of which we are treating is the most conspicuous. The clefts chiefly pass level places, and as they intersect craters,

they are thus shown to be of more recent date. They are considered to be caused by the contraction of the lunar surface as the body of the moon cooled. The cleft in the photograph intersects a small crater called Hyginus. There is no treason whatever for considering these clefts to be of artificial origin The largest of the craters in this view is called Agrippa. This has the usual central cone. The other craters in the view have no special features ; the one at the bottom has a central cone, and thei'e are indications of a cone in the one rather high up and to the right. The original photograph was taken by Professor Pickering of Harvard College Observatory.

We have now to deal with the origin of the most remarkable features on the moon's surface. Volcanic action on the moon is now supposed to have ceased, although some observers have asserted that changed have been noticed from time to time, leading to the inference that some of the craters are not yet wholly extinct. If there are any smouldering volcanic fh'es occasionally in action they are inconsiderable, and are as nothing to the fearful scene once enacted when the whole lunar surface was an incouceivable chaos from thousands of volcanoes belching forth fire, scoria and stones to enormous heights in every direction. The ramparts surrounding the craters are in some cases eighty miles across. This means that the cone in the centre has ejected matter with sufficient force to hurl it about forty miles distant. To enable it to do this, it would probably throw the ejected matter to a height of about thirty or forty miles. This seems almost incredible, but it must be borne in mind that the force of gravitation on the moon is much less than on the eai'th. A cricketer could throw a ball with the same exertion six times as far on the moon as on the earth ; and as a modern cannon would with pi'oper elevation easily throw a shot six miles, the same cannon transported to the moon could hurl the shot from thirty to forty miles. The theory of the formation of the lunar craters is shown in the accompanying sections of

one. The first figure of the two represents a volcanic vent when the crater was in full activity, and throwing forth a fountain of ashes or stones to a great distance. These materials, accumulating, pile themselves up till they form the wall or rampart surrounding the crater. In the second picture the explosive power has become enfeebled, and perhaps for a time, altogether exhausted. The volcano, on bursting again into activity, has only a small part of its former energy, and a comparatively feeble eruption ensues. The material now thrown up falls back near the vent, and raises a conical mountain in the centre of the rampart. The flat floor, which is found in Archimedes and other craters, has probably resulted from an overflow of lava which has become consolidated as before touched upon.

The systems o of bright streaks, radiating chiefly from seven different craters, are very remarkable phenomena. The most remarkable system of these bright rays or streaks radiates from Tycho. The rays are best seen when the moon is fall, and it i& suggested that they may be ancient lava streams fbleached by the chemical action of fumes from the interior. Nasmyth says the streaks or cracks are caused by explosion, ",the disruptive force being the expansion which precedes the solidification of molten substauces of volcanic origin." The cracks,. Nasymth considers, were then filled up with molten matter from beneath. There are more than one hundred of these fissures that can be counted radiating in all directions from Tycho, some of which extend well over the moon's hemisphere.

In looking at some photographs of the moon one cannot fail to be struck with the resemblance these fissures present to the lines of longitude radiating from the poles on a terrestial globe. A familiar illustration or comparison can also be found in an oi'ange when peeled, as the lines dividing the fruit into segments radiate from two centres. Nasmyth filled a large glass globe with cold water, and hermetically sealed it, and then placed it in a bath of hot water. The cold water inside the globe expanding

with the heat more rapidly than the glass, the globe cracked in lines radiating from the point of least resistance, resembling the lines radiating from Tycho, A photograph of the glass globe, as given in Nasmyth and Carpenter's beautiful work on the Moon, is here reproduced. The resemblance to the lunar fissures is so striking that to many minds Nasmyth's ingeneous theory will amount to demonstrated facfc. The moon, like the earth, was once in a molten state, but the moon being so much the smaller cooled first. The larger the mass of a body the longer it will take to become cold. A

small iron or other casting will rapidly 0001, whilst a large casting will take many days to part with all its heat. Our sun, owing to his vast size, will take perhaps millions of years to cool, but it will burn out and become an inert and cold body at last. So far as is known there is nothing lasting in the whole visible universe — suns come and go, solar systems wax and wane — . . Dead worlds linked to a burnt-out sun, Cinders tossed to the Immeasurable Void ! Celestial derelicts Out of the way removed lest mischief they should cause. The moon's disc, so far as the most

delicate measurements can determine is, perfectly circular, and does not exhibit any flattening at the poles like our earth and some of the planets. This is what we should expect to be the case owing to the slow rotation of our satellite on its axis, which takes (nearly) twenty-seven days eight hours ; and this period synchronizes with its period of revolution in its orbit round the earth. The moon's motion in its orbit is very complex, and has called forth the highest powers of the greatest mathematicians of modern times. Allusion was made in the former article to the friction of the

tides raised by the moon, acting as a break, causing the earth to gradually rotate more slowly. Professor Gray, Lord Kelvin's successor at the Glasgow University, estimates that the earth falls behind a true clock about twenty-two seconds in one hundred years. Professor Gray further says : — " With respect to the origin of the moon, the earth at an early stage of its existence was a semi-solid, semi-fluid, plastic mass, spinning round on its axis in a period of three to five hours. The period in -which a wave would have gone round the earth would have been about three hours, or nearly

equal to the period in which the earth went spinning round. Now, if a wave produced by the action of the sun went round the earth in three hours, each time it returned to receive the sun's action it would be increased in size. The earth was spinning at a great rate ; and the result would be that parts of it would fly off like the rim of an over-driven fly-wheel, and one or more of these fragments formed the moon. The moon continued to go round in a similiar orbit to the earth, but rather more slowly

than when it left the earth. Immediately it began to !go further and further out, and this was what it was still doing." The " slowing-down " of the earth's rotation is thus less than a quarter of a second in a year. The length of the day and month are both increasing. After a long interval there will be another change, and the moon will approach the earth again. These changes, however, will take enormous lengths of time to bring about. How marvellous is the infinitely complex system of nature ! What delicate balancing of forces, what adaptations of means to ends !

The question of course is asked, is there life on the moon ? and it has generally been answered in the negative. It has until lately been considered that there is no atmosphere and no water or moisture ou the lunar surface, and life, either of plant or animal, appears to be an impossibility without water, but Professor Pickering's late observations would seem to indicate vegetation and a slight atmosphere. The probabilities are that some lowly forms of plants and animals exist even in the apparent desolation of the moon. Nature can doubtless adapt forms of life suitable to tho environment under the most varied conditions. Even in the deepest ocean, life exists under a pressure of tons to tho squaro inch. We have no actual knowledge of the existence of life in any form on any of tho celestial bodies around us (although it is highly probable that it does oxist), and certainly no knowledge of the existence of intelligent beings upon them.

The so-called " canals " on Mars arc very apocryphal. They are some forty or fifty miles wide, and appear double, and are conceivably strips of irrigated land fed by artificial means, but this is considered very doubtful. As to electric signals being made from Mars to the earth, and read and understood in our present state of knowledge, we might as well expect to exchange messages from New Zealand with the Patagonians with the aid of a couple of stable-lanterns ! It has been suggested that if an enormous equilateral triangle with sides say 300 or 400 miles long was ploughed up on some great plain on the earth and sown with a crop say of wheat the changes of colour aB the crop came up and I'ipened might be noticed by inhabitants (if any) on Mars if they had powerful telescopes or other optical means ; and that if they replied by another similar triangle or geometrical figure, an exchange of intelligence would have begun. This would appear to be the only likely means of signalling to Mars with any prospect of success. The next step might be to show our new acquaintances the gigantic figure of a man to enable them to form an

idea of what we are like, to which they might respond with a portrait of themselves. Of course it is possible that the Martians may have higher intelligence than ourselves, or have greater command over the forces of nature, but it is equally probable that the reverse may be the case. As matters stand at present inter-planetary communication is little more than a dream. Under the most favourable circumstances Mars is about 150 times farther away from the earth than is the Moon, and its apparent dimensions would equal half-a-sovereign at a distance of 2,00u yards ; in other words, when Mars is nearest to us, half-a-sovereign placed 2,000 yards from the eye would just hide Mars.

It is of course well known that the moon emits no light of her own, but shines entirely with light reflected from the sun. There is another fact, however, that perhaps is not so well known. A day or two before and after new moon, when it appears as a bright narrow crescent the rest of the lunar

disc is seen faintly illuminated. This is caused by light from the sun reflected by the earth on to the moon, which in her turn reflects it again back to us. When the moon is in the crescent stage it is observable that the bright part appears to be a segment of a larger circle than the faintly illumined part lit by the earthshine. This is owing to irradiation, which causes a bright body on a dark ground to look a little larger than it really is.

Although the sun and moou appear in the heavens to be nearly the same size, the sun is really nearly sixty million times as great, and he is about 385 times as far away. If we imagine the earth to be placed in the centre of the sun, the moon would then revolve in her orbit inside the solar sphere about midway between his centre and his surface. This consideration enables us to form some idea of the vast dimensions of the great fountain of light and heat that luminates our solar system.

Erratum. — In the Article on the opposite page^ in the eighth line of the second column, for though, read through.