THE BIRTH OF THE MOONTHE LENGTH OF THE DAT.

Patea Mail, 2 June 1882, Page 1 (Supplement)

THE BIRTH OF THE MOON—THE LENGTH OF THE DAT.

At present, no doubt, the effect of the tides in changing the length of the day is very small. A day now is not appreciably longer than a day a hundred years ago. Even in a thousand years the change in the length of the day is only a fraction of a second. But the importance arises from the fact that the change, slow though it is, lies always in one direction. The day is continually increasing. In millions of years the accumulated effect becomes not only appreciable, but even of startling magnitude. As thousands of years roll on, the length of the day increases, second by second, and the distance of the moon increases mile by mile. These changes are never reversed. It is the old story of the perpetual dropping. As the perpetual dropping wears away the stone, so the perpetual action of the tides has sculptured out the earth and moon. Still the action of the tides continues. Today is no longer than yesterday; yesterday is no longer than the day before. A million years ago the day probably contained some minutes less than our present day of 21 hours, retrospect does not halt here ; we at once project our view back to an incredibly remote epoch which was a crisis in the history of our system. Let me say at once that there is great uncertainty about the date of that crisis. It must have been at least 50,000,000 years ago. It may have been very much earlier. This was the interesting occasion when the moon teas horn. I wish I could chronicle the event with perfect accuracy, but I cannot be sure of anything except that it was more than 50,000,000 years ago. At the critical epoch to which our retrospect extends, the length of the day was only a very few hours. I cannot tell you exactly how many hours. It seems, however, to have been more than two and less than four. If we call it three hours we shall not be far from the truth. Perhaps you may think that if we look back to a still earlier epoch the day would become still less, and finally disappear altogether ! This is, however, not the case. The day can never have been much less than three hours in the present order of things. We have seen the moon revolve around the earth in an ever-widening orbit, and consequently the moon must in ancient times have been nearer the earth than it is now. No doubt the change is slow. There is not much difference between the orbit of the moon a thousand years ago and the orbit in which the moon is now moving. But when we rise to millions of years the difference becomes very appreciable. Thirty or forty millions of years ago the moon was much closer to the earth than it is at present: very probably it was then only half its present distance. We must, however, look still earlier, to a certain epoch not less than 50,000,000 of years ago. At that epoch the moon must have been so close to the earth that the two bodies were almost touching. I daresay this striking result will come upon many with surprise when they hear it for the first time. It was, I know, with great surprise that I myself read of it not many mouths ago ; but the evidence is unimpeachable, and it is surprising to see how such information has been gained by merely looking at the ripples of the tide.

It would require the combined powers of a poet and a mathematician to pourtray the scene with becoming dignity. I have only promised to give you that glimpse along the Corridors of Time which I myself have been able to obtain. The scene is laid in the abyss of space ; the time is more than 50,000,000 years ago; the dramatis persona are the earth and the moon. In those ancient times I see our earth to bo a noble globe, as it is at present. Yet it is not partly covered with oceans and partly clothed with verdure. The primmval earth seems rather a fiery and half-molten mass, where no organic life can dwell Instead of the atmosphere which wo now have I see a dense mass of vapours, in. which perhaps all the oceans of the earth are suspended as clouds. I see that the sun still rises and sets to give the succession of day and night, but the day and the night together only amount to three hours nstead of twenty-four. Almost touching the chaotic mass of the earth is another much smaller and equally chaotic body. Around the earth I see this small body rapidly rotating. The two revolve together as if they were bound by invisible bands. This smaller body is the moon. Such is the picture which IJ wish to present to you as a glimpse through the Corridors of Time. —From “ A Glimpse through the Corridors of Time,” by Professor JR, S. Bell, in “ Nature.”