Scientific Lectures. 49 



volcanoes had just been burning there, thev account for all the resem- 

 blance in the ragged walls, in the cone inside the mountain, in the 

 openings of the small craters along the sides, shadows and all. Yol- 

 canic action might go on in the moon on an awful scale. Why ? 

 Because things weigh one-sixth there what they do here, and fire 

 might act with prodigious intensity. Tou might jump, if you had 

 the muscular energy preserved to you, six times as high as on the 

 earth, and you would be six times as long coming down. Things are 

 thro^vm, up there, more easily. And the moon is not made of such 

 stern stuff as the earth. The density of the earth is five times that of the 

 moon. Yolcanic fire might there have an awful arena for exhibition ; 

 and, accordingly, there are great craters, probably fifty, sixty, almost a 

 hundred miles across, and three miles deep. " Do you think, sir, 

 there are mountains in the moon ? " I may be asked. Do I think so ? 

 My dear sir, that is beyond the region of " I think ; " I hiow there 

 are. But examine the sun once, and what do you see on it ? It has 

 not a uniform bright surface, but you see it broken by black spots. 

 Those spots seem to indicate that they are hollows ; although I can- 

 not stop to insist upon that. But those spots are hollows below the 

 surface. How large are they ? [The lecturer here illustrated from 

 the diagram the relative size of the sun and the planets that surround 

 it.] The diameter of the sun is a hundred times the diameter of the 

 earth. The surface is equal to 100,000 oceans much larger than the 

 Pacific; all that is full of agitation throughout, and tossed into 

 waves of insufferable splendor, thousands of miles long. Oh, when 

 we look at the sun, as like a giant he begins his daily course, or when 

 arrived, in full-orbed meridian splendor he almost seems to pause a 

 moment to look down upon the world rejoicing in his presence, or 

 when he sinks to rest, arraying himself in the splendid garments of the 

 evening, under any and all those circumstances he is at once the fit- 

 ting representative and the chosen emblem of all that is great and 

 beautiful. How large are these craters ? [The lecturer here pointed 

 out a crater represented on the diagrarn of the sun.] Look at the 

 earth and see how easily it could drop in, and how much 

 margin would be left. These great openings open and close 

 sometimes in the space of three or four days. The changes are 

 prodigious. "W"e cannot stop, however, to speak of the struc- 

 ture of the sun any further than to say that the stereoscope has 

 told you, that there is iron there, and magnesium, and sundry other 

 things. The phenomena of Mars, we noticed by the telescope a few 

 [Inst.] 4 



