. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. op Gravity , •»*- on the Moons Path. the arc described by the Moon in one minute, the length of which is found by the following proportion to be nearly 33:— 27d. 7h. 43m.: lm. : : 360° : arc described in lrn. The arc MJV, then, being 33 for one minute of time,the length of MA can be readily calculated; it is foundto be 16^- feet when ME equals 240,000 miles. That is,a body at the Moons distance f
. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. op Gravity , •»*- on the Moons Path. the arc described by the Moon in one minute, the length of which is found by the following proportion to be nearly 33:— 27d. 7h. 43m.: lm. : : 360° : arc described in lrn. The arc MJV, then, being 33 for one minute of time,the length of MA can be readily calculated; it is foundto be 16^- feet when ME equals 240,000 miles. That is,a body at the Moons distance falls as far in one minuteas it would do on the Earths surface in one second; inone second, therefore, by Rule III. Art. 499 (as 60s. makelm., and 602 = 3600), it will fall but -^g^o of the distanceit would fall in one second at the Earths surface. Now, the Moon, being 240,000 miles from the Earthscentre, is just 60 times as far from it as an object at the How far would it fall in the same time at the Moons surface? 506. Give thereasoning by which this fact is arrived at. How, as far as distance is concerned,is the force of gravity thus experimentally found to vary ? What did this calcu-. 278 UNIVEKSAL GKAVITATION. Earths surface is, and we have seen that it is affected bythe Earths attraction only -g-^-g- as much. Its distance is60 times greater, its gravity is 602 times less. Thus theforce of attraction is experimentally found to vary in-versely as the square of the distance. It was this calcula-tion that revealed to Newton the law of universal gravita-tion. 507. Keplers Laws.—Long before Newtons discovery,Kepler, from observations of the planets merely, haddetected certain laws of their motion, which bear hisname. They are as follows:— I. Each planet describes round the Sun an ellipticalorbit, and the centre of the Sun occupies one ofthe The radius-vector of a planet describes equal areas in equal If the square of the time of revolution of eachpl
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectastronomy, bookyear18
