TOPICS OF THE DAY.

Nelson Evening Mail, Volume XLIII, Issue XLIII, 11 September 1909, Page 2

TOPICS OF THE DAY.

Followinjr on from the subject deait with in the Why the leading article, Earth is Habitable. where it has been seen that it is Nature's work to make even barren places habitable, it is interesting to observe why the earth is habitable. For life of any kind innumerable conditions have to be narrowed down to a fine margin. They have been clearly put by Dr Marshall in a recent lecture at Dunedin. "lie first of all drew attention to th& frailty of the human form, pointing out that it could only exist in a certain sot of circumstances. Human life is only possible between certain narrow limits of temperature, it reqniresan atmosphere, water must be abunilant, and a food supply must be available. This equable temperature oblains so i'ar as we can judge on the i.irth alone. On our nearest neighbour, the Moon, the day is as long as 14. of our days, and all. this time the Sun's rnys are beating down unhindered hy any atmosphere. It has been calculated that the temperature can rise to 600 degrees. Then the long night, as long as 14 of our days, sets in, and with no atmosphere to retard the radiation of heat, the temperature mustfall to quite 150 degrees below zero. Even- among the planets of our own solar system, the earth is alone in having a temperature within the required limits. On the planet Mercury tho sun'a heat is nine times as intense as it is herb, and on the furtherest planet, Neptune, it is only one nine-hundredth. S possible exemption ia Mars. "To- proceed further, in having an atmosphere the Earth Atmogphero is, again exceptional, and The Moon has none, Light. tho great space through which wo move has none. Mars appears to have an atmosphere, and large' clouds of aqueous vapour- have been observed. Carbon dioxide in the atmosphere is necessary to plant life ultimately for our food supply. Other constituents are' necessary in delicate proportions, and in the atinosphoro of the Earth alone all these conditions seem to be realised. Water is known to chemists as the typical neutral substance, and this property enables it to perform functions that- nothing else can fulfil. ; In tho 'Moon tho ocean "is dried up. In the hotter bodies the ocean is in the atmosphere as steam. Although light ig necessary to life, it must be observed , that throughout space eternal darkness prevails; at least as intense as that of a starlight night. On Me'rcurv the light would bo too intense for tl(e human eye; the Sun would have three times tho diamoter it has here. On Neptune the Sun- would give only oiiohundredth of tho. light it gives us. Another fact that leads to. make life possible here is the arrangement of the seasons. On the Moon the long day and the long ni«ht would be againet growth. The Moon always turns the same side to the Earth. In time the Earth will always turn the same face to the Sun, and there will be no day and no night and no seasons. Dr Marshall pointed out that these -seasons could not havo existed for long"—^on account of temperature. The Earth can havo been habitable for for more than 'ten million years— a short time geologically. 6

Wlien Professor David, of Sydney, speaks on scientific The subjects, especially Ivortn Pole. in regard to Arctic and Antarctic questions, he is entitled to an. "attentive hearing." .In the first place he points out the importance of-the reaching „f the North Pole, and remarks that tho -geographical poles are in theory great ojistinguishing centres of tho earth'? atmosphere. At the Poles, according to theory, as he reminded an interviewer, the air which has arrived there is by a path high overhead from the Equator, descends to the earth, and then blows back Equatorwarda. The Poles art- the hubs of the atmospheric univerj«.. as well a.o being the axles of tho eaifh's rotation. The verification of this the..'.y vould be a most important contribution ♦o meteorology. It would be most interesting to know tho exact temperature at the Polo, for many .sriontists iiave held that the Pole is not necessarily i,hfi coldest part, because of the descent of the air carried up from the Equator. Professor David explains that. iais great polar air vortes might be about ICO miles across. If there i» land- at tho Pole its geological formation would be interesting. In Greenland, and uea 1 * it, there havo bean found fqs.tll points which show the climate was onoe temperate, there. Fossil remains of animals or plants found anywhere near the Pole, Professor David pointß out, would be of intense scientific value. Th3 discovery of plant or animal fossils might (affect the bipolar theory of tho <icvelopnient of life, which i- thf.t iife commenced on both Poles .>{ tlio ennb at once an-1 spread Equntorwurds. llio assumption is that the earth was Sit one time too hot about tho Eqnitor for '.ife to exist. The Poles would be the first spots to cool, and life woiiid arise tiiere.