CHANGES IN THE MOON.

Auckland Star, Volume XX, Issue 245, 15 October 1889, Page 3

CHANGES IN THE MOON.

OBSERVATIONS BS* PROFESSOR

LAMBERT.

Another change in the moon is reported to j.ave taken place ; I refer to the alleged alteration in the crater Plinius. It will be remembered by many that similar reports have several times come to hand within the last fifty years, and from some of our best observei-3. The old idea, thab it would be possible some day to "discover signs of actual life upon our moon, has now bub few supporters, while many of our astronomers cling stronger than ever to the hope of discoveringchange in her inert mass. But while this hope is sound andcaptivating, whiletrom time to time we may expect to learn of such discoveries, we must nob rush hurriedly inbo the belief that they have actually been made when such reports reach us ; for while it is easy to suspect change on a /surface like the moon's, while ib is.scientific bo expect such discoveries bo be made, y?e must remember that we are not looking at an object a few feeb away from us, and that things out yonder are not always as they seem. Anyone who has studied the moon's surface from month to month will know well how varied the same object appears under different' illumination, and how easy it would bo ab one time more than another to suspect change here and there of an actual order. Such observers as Schroeter and Gruithuisen, whose accurate observations Could hardly be questioned, made this very mistake, as Beer and Maedler pointed out and corrected. In November, 1866, Dr. Schmidt, chief of the Athens Observatory, announced that the crater Linne, situated in the SeaOf Serenitz, was missing, and that its place was occupied by a whitish cloud surrounding a most minute crater. This crater was described by earlier observers as at least five miles in diameter, and very deep., After l)r. Schmidb's announcement other observers described ib as undergoing change in form and dimensions almost daily, bub it is now known that the changes noticed were for the most part due bo the varying circumstances of illumination, induced by combinations of libratory effects' added to the ordinary changes depending upon the direction of the sun's rays. It ■would appear, however, thab this crater is not actually missing as Schmidt supposed, but ib is certainly no longer deep. Another change was announced in May 1877 by Dr. Klein. He was observing in the neighbourhood of the well-known crater Jiyginus, near the middle of the visible half of the moon, when he observed a.small crater full of shadow, "apparently ahoub three miles in diameter. De had frequently observed this same region during preceeding yeai-3, and felfc certain that no such crater existed in 1876, for ib formed co conspicuous an objecb in the _ Sea of Vapours thab ho could nob have missed ib. The greab.chart by Beer and Medler which Ims a diamater of 37 inches and Lohrman's excellent map of 15 inches diameter, were both carefully searched, but no such crater as that announced by Dr. Klein was found. Ifc appeared thus far'that a new crater had really been discovered in the moon, but subsequent research was destined to throw some considerable doubt upon the matter. The photographs of Rutherfurd, De la Rue, Ellery, and Draper of our satellite taken prior to 1877 were examined; and as these show objects le-ss than two miles in diameter, they were reasonably expecbed to give very deciaiveevidence on this interesting subject. After every care had been taken in the examination of these photographs, the result was that no such crater as that described by; Dr. Klein was found in any of them. But in a splendid photograph by Rutherfurd, on March 6th, 1865, the place of Dr. Klein's crater is occupied by a small spot, brighter than the Sea of Vapours in which it stands. Now, this is the usual appearance of a small crater under a high sun, but whereas rib sil-h crater is shown on the later photographs, bub is revealed by one taken twelve years prior to tho announcement of its discovery by Dr. Klein, some considerable degree of doubt is thus thrown -upon the suggestion that-, any recent change has taken place in that particular locality. While, therefore, it is so easy for our best observers to misinterpret. what they see upon our moon; while it.ia so difficult' to interpret aright what is seen owing to the many difficulies by which the subject is surrounded, the reported change in Plinius should be accepted with strong Erobability only, until careful observation as been made under every possible illumination. But while I have endeavoured to show

that.the alleged changes on the moon in the past have scarcely been proved, I am not for a moment contending that the moon has assumed her final condition, (that is,

ihafc she has. attained to such a condition when no further change is possible.) On the other hand, there is no member of the Solar System perhaps, so likely to _undergo change as our moon. Nor is it necessary to seek an explanation in scarcely any change the moon can now undergo in the theory of volcanic forces. Anyone who studies Mr Mallet's admirable theory of volcanic energy will, I think,,be convinced that however well it applies to our earth, that it finds as good, if not a bettor interpretation in-the present condition of our satellite. It seems to me., that if evidence of continued volcanic action is to be sought in the moon, the place to look for it is around the circumference of the disc,

-where eruption from any marginal orifice r.weuld manifest itself in Uie form of a prov jtruding haziness, as Nasmyfch long ago • pointed out: bub such an appearance has never, to my knowledge, been detected.: If we want a cause for the change we may j expect upon the moon's surface, we shall find onesuffieiently adequate in the violent alternations of temperature to which that surface is exposed dining a lunar day arid night. 'For fully 300 hours know the sun pours 'down upon the lunar surfacehis heat, uninterrrupted by cloud, and untempered by any atmosphere, until her surface becomes heated to a degree which is estimated at 600 degrees Fahrenheit, the fusing point 'Of tin or bismuth.. Then during her long ; night of corresponding length, this heat is 'entirely radiated away until her surface cools down again to a temperature which -has been calculated to be 250 degrees below -the zero of Fahrenheit's scale. These - figures are the results of very careful experimental investigation by Lord Rosse with his six feet reflector, and have since been confirmed by the French observer, •Marie Davy. It seems to me that such a severe monthly range of heat and cold as . ,760 degrees Fahrenheit cannot but pro- > duce very material and telling effects upon ! some, at least, of the component materials of 'the moon's surface, and that sooner or later j "some of the familiar details of her -surface ,musfc undergo more or less change. • If careful observation should, in "the course of '\t_me. prove that changes have taken place 'in the crater Plinius, there seems to me no reason why we should not find a clear and ; adequate .cause for such in the. conditions we have just considered, f6r it is\ perfectly clear that such extremes of temperature, I conducted in such rapid succession, and ■ through such long ages, must disintegrate .some parts of the surface at least, and in '•:•' time modify the selendgraphic contour. ~:';. Against this view it has been urged that Utile moon's surface matter is composed .chiefly of crystalline and porods lavas, which would be HUely to withstand £he :fierce extremes of temperature, thus rev . ducing the probability of.change through the v) cause we have been considering to a mini- <! mum. Buis whatever force'there may be '< _ Ja this. argument, whatever may be the molecular structure of that "face of the ... «noon we see, it is obvious, I think,' that -J where material is heaped in detached : '.-'ißßliJwa'a-we'seeit on the moony that there

will be a grating and fracturing, of such masses against each other through the alternate expansions and contractions of the entire crust, and that eventually these detached masses will be dislodged and fall to the lower levels. In this way lunar craters may be wholly or partially filled, up*, their interiors become modified, and the whole lunar landscape become gradually changed. S. J. Lambert.