THE MOON 331 



CHARACTERISTIC LUNAR SURFACE FEATURES 



CRATERS. Undoubtedly the most striking of these 

 features is what is known as the craters, a name derived 

 from their likeness to the mouths of terrestrial volcanoes, 

 a resemblance, however, that is only skin deep, and 

 means nothing. To make out the general contour of 

 these peculiar figures, no higher telescopic power is re- 

 quired than Galileo had available, and the probability is 

 that with his first glance through the instrument he in- 

 terpreted them as indeed volcanic; and that interpreta- 

 tion is the one which, in spite of later arrivals, commands 

 the largest following to this day. The only other hypoth- 

 esis that may be said to have gained anything like gen- 

 eral acceptance among professional astronomers is that 

 formulated by Professor G. K. Gilbert, in 1892, and 

 known as the Bolide or Impact theory, which holds that 

 the Craters are the pit holes made by the blows of fallen 

 meteorites. 



These lunar craters vary incredibly in size, ranging 

 as they do from more than a hundred miles in diameter 

 down to a size hardly perceptible through the best tele- 

 scopes ; indicating clearly that, for aught we can say, they 

 may exist even as narrow as a few feet, or even a few 

 inches ; which is what I claim to be actually the case. In 

 the multiplicity of their visible number these craters are 

 no less remarkable, running literally into the thousands ; 

 and they are, also, amazingly diversified as well yet, 

 for all that, there is no mistaking their general kinship. 

 This latter consists in two things, namely, that they all 

 possess a surrounding wall or circumvallation, and, sec- 

 ond, that the land craters are bolder in relief and more 

 sharply outlined than their squat brethren on the maria 

 floors. To all intents and purposes, indeed, the maria 

 themselves are indistinguishable from the craters, save in 

 the one particular of size. 



Their individual differences, however, are legion. 

 In some craters the encompassing walls are as much as 

 four or five miles in height, while in others, even of very 

 large ground plan, the rampart is scarcely tall enough 



