. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. Insize they range from craterlets barely visible in the most[X)werful telescopes to the great ringed plains 100 miles ormore in diameter. One writer even regards the lunar Car-pathian, Apennine and Caucasus mountains as but the frag-ments of a former huge crater wall which had a diameter of800 miles. Generally the bounding wall is approximatelycircular and is compound, composed of shorter ridges whichoverlap one another, but al
. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. Insize they range from craterlets barely visible in the most[X)werful telescopes to the great ringed plains 100 miles ormore in diameter. One writer even regards the lunar Car-pathian, Apennine and Caucasus mountains as but the frag-ments of a former huge crater wall which had a diameter of800 miles. Generally the bounding wall is approximatelycircular and is compound, composed of shorter ridges whichoverlap one another, but all trend concentrically. The inner ° Direct measurement gives slightly the larger value, but this is due chiefly toiiradiation. Measures of a bright disk like that of the Moon or of one of theplanets are always a little in excess of the true values. An excellent illustrationof the irradiation effect is found in the appearance of the Moon three or fourdays after new Moon; the bright crescent aiipears distinctly larger in radius thanthe dark portion feebly visible by reflected earth-light, a fact embodied in thephrase the new Moon holding the old Moon in its PLATE XIX. Walled Plains on the (Sunset) Terminator. The upper, double walled plain, with triple central peak and a bright rillconnecting the peak and wall at the right is Petavius. Below isVendelinus. Note the small craters on the walls and floor of Ven-delinus. The Moox 89 plain or floor is lower than the plain, oftenthousands of feet lower. Theophilus, for example, a crater64 miles in diameter, is 19,000 feet deep. The crater walls,as a rule, slope very steeply to the inner floor and much moregently to the outer plain. Frequently one or more mountainpeaks tower abruptly from the inner plain of a large crater to aheight of even feet as in Copernicus, or 16,000 feet as inTheophilus; but these peaks never, according to Neison, reachthe altitude of the crater walls. Finally, the craters overlapo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectastronomy, bookyear19
