Rensselaer Journal, Volume 11, Number 30, Rensselaer, Jasper County, 2 January 1902 — MEASURED PLANET MERCURY. [ARTICLE]

MEASURED PLANET MERCURY.

Dr. See of Washington Find* Diameter to Be 8858 Mlles. Dr. See of the United States naval observatory in Washington has just concluded a measurement of the planet Mercury with the large telescope of that institution. Its diameter is found to be 2,658 miles. Dr. See calls attention to the fact that he has never observed any marked spots on the planet’s disk, not even when the sky was absolutely pure and the image of the planet perfectly defined on the lens of the telescope. His observation also is that there is no diminution of brightness at the edges of the disk, such as would be produced by an absorbing atmosphere. Although these results agree in general with those obtained at the Lick observatory, they disagree with those of Schiajarelli and Mr. Percival Lowell. Dr. See has made another interesting estimate regarding meteors. Every observer notes a considerable number of small meteors while he is engaged in telescopic observations. The field of view of a telescope is a very small fraction of the surface of the heavens, and a simple proportion based on the number of meteors enables an estimate to be made of the number of meteors in the whole sky. In this manner, says the Washington Star, Dr. See there are about 1,200,000,000 telescopic meteors appearing in the sky daily. Between 10,000,000 and 15,000,000 meteors, bright enough to be visible to the naked eye, encounter the earth daily, according to the estimate of Prof. Newton. When the Day Was Five Hours Long. We all know that the earth revolves on Its axis once in twenty-four hours. Millions of years ago the day was

twenty-two hours; millions of years before that it was twenty-one hours. As we look back into time we find the earth revolving faster and faster. There was a time, ages ago, wljen the earth was rotating in a day of five or six hours in length. In the remotest past the earth revolved in a day of about five hours. It could revolve no faster than this and remain a single, unbroken mass. When our day was about five hours long the moon was in contact with the earth’s surface. It had just broken away from its parent mass. As the length of the terrestrial day increased, so did the distance of the moon. Whenever the rotation time of a planet is shorter than the period of revolution of its satellite, the effect of their mutual action is to accelerate the motion of the satellite and to force it to move in a larger orbit —to increase its distance, therefore. The day of the earth is now shorter than the month, the period of revolution of the moon. The moon is therefore slowly receding from us, and it has been receding for thousands of centuries. But the day of the earth is. as we have seen, growing longer. The finger of the tides is always pressing upon the rim of our huge flywheel, and slowly but surely lessening the speed of its rotation. So long as the terrestrial day is shorter than the lunar month the moon will continue to recede from us. —New York Herald.