The Ashburton Guardian. Magna est Veritas et Prævalebit. SATURDAY, OCTOBER 5, 1889. WHAT'S THE MATTER WITH THE MOON.

Ashburton Guardian, Volume VII, Issue 2245, 5 October 1889, Page 2

The Ashburton Guardian. Magna est Veritas et Prævalebit. SATURDAY, OCTOBER 5, 1889. WHAT'S THE MATTER WITH THE MOON.

A day or two ago news camo from the Government observatory at Sydney, of some remarkable changes which have taen going on m the earth's silent satellite, and which it seems were fi«*st noticed from the observatory at Geneva. ' Mr Russell, the Sydney astronomer says that he finds that " two mountains have disappeared f and two conspicuous craters have taken their place. One of these is a mile and three quarters m diameter, and the other is somewhat larger. Two small craters arc also visible. The large crater is surrounded by a white wall, the material composing which haß apparently been freshly thrown up." In view of all this a contemporary very naturally puts the question, " What's the matter with the moon ?" and m reply thereto explains that that luminary is now and has often been before the scene of great volcanio activity. It then proceeds to give the following interesting information.- The new craters discovered by Mr Russell, though huge m comparison to the dimensions of the orater of any volcano on the earth, " are mere babies to some of the lunar craters, which run up to 100 miles m diameter. The larger ones are like vast plains, surrounded by high and steep mountain walls, the plain being usually lower than the region outside the walls. In the case of one very large crater, however, the crater plain is level, or nearly level, with the top of the surrounding wall. Sovoral attempts have been made to account for the formation of such large craters m the moon. One idea deserves mention on account of its own peculiarity : it is suggested that they were formed by the fall of large meteoric masses from space, the larger craters presenting just the appearance produced by dropping a weight into a pasty substance, and no doubt the fall with solar velocities, of meteorites weighing some thousands of tons, would melt both the meteoritep and the surfaces they struck into a paste. A more probable view is that lunar volcanoes are attribatable to the same cause which produces terrestrial volcanoes, the crushing of the outer cooled portion as it sinks upon a cooling and shrinking inner portion It is a simple matter of calculation whether the iorce of gravity on the moon is sufficient to cause such forcible contraction, and m doing ho to produce heat enough to melt ordinary rock substance or metalo, and the calculation being made fchows that the force is sufficient. The crushing preßsura of such contraction is equal to the weight of a wall of the moon's matter, of a height equal to one-fourth of her diameter, that is, a wall 576 miles high. Supposing the moon's crust material to be of the same nature as the earth's, but only one half as dense (the whole moon having only half the average donsity of the whole earth), say one and a-half times as heavy as water, the weight of such a wall on the moon (where griTity is but '163 what it is on the earth's surface) would be about HO tons per square inch of its baße. This is sufficient to crush and melt most if not all terrestrial rocks, and set up volcanio action, and that pressure may by not improbablo circumstances bo doubled or even trebled. Allowing that the moon's interior is still cooling and shrinking, there is force eDough m the gravitation of her cooled crust to melt some part of it as a consequence of the shrinking of the interior. Other results of crust pressures are scon m chains of mountains-?— • wrinkles ' — said to be 20,000 feet high. A peculiar thing about the lunar volcanoes is the disappearance of the molten matter after it has been emitted, and has filled up high walls around the limits of its spread. This disappearance seems to take place so rapidly as to suggest that the moon containß cavernous spaces below the region whoro the volcanio forces operate, into which the molten matter presently finds its way before it has had time to cool— save m the case of the largo crater above referred to, which remains filled to the brim of its walls. According to this view lunar eruptions consist of emissions of molten material which spreads around the vent and continually fences itself m by moraines of cooled slag ; the molten matter presently eats its way through internal barriers and sinks into the cavernous interior, leaving behind it a mountainous circular moraine of chilled slag — the 1 crater wall,' — and taking with it a more or less considerable depth of the previous surface melted while lying upon and flowing off it, thus forming a crater plain at a lower \^\ ftw * be surrounding country."