48' Transactions of tee American Institute. 



the snn, in wliicli last, however, he was anticipated by Harriott, in 

 Enghmd." This^ was at the beginning of the seventeenth century. 

 But we have ah'cady mentioned several interesting objects that the 

 telescope had thus brought to view. "What were they ? Satellites of 

 Jupiter ? Tes. Here is one of them [pointing it out npon a dia- 

 gram]. Here is the form of the disc of Jupiter, which is a great deal 

 better seen in modern telescopes. Jupiter has four satellites, and 

 here is the shadow of one of them npon the f;ice of the planet. These 

 are the belts of Jupiter, which are supposed to be substances in his 

 atmosphere ; for Jupiter is now proved to have an atmosphere ; and 

 thus it is M'ith Mars, and with Saturn. How is it proved ? By 

 means of the spectroscope. How does the spectroscope show it? 

 Assuredly I will not anticipate the lecture by explaining it. There 

 are substances floating in the atmosphere of Jnpiter. His shape is 

 not round. It is much shorter in a north and south direction than in 

 the otlier. He turns round in less than ten hours, and the outward 

 fling of that turn swells out notably on one side, so that you can see at 

 once that he is not round. But at the same time Galileo saw the 

 moon. What do we see wlien we examine the moon with the tele- 

 scope ? The edge of it is all ragged ; when if it were a smootli globe 

 it ought to be smoothly cut ; and in the quarter-moon when the edge 

 of the circle is turned toward you, as the edge of the glass, it ought to 

 appear a smoothly cut straight line. It is not a smoothly cut straight 

 line by any means. The moon, then, is horribly rough. The moun- 

 tains are struck by the sun's rays before the plains receive them. The 

 tops of the monntains will therefore appear illuminated, like a ronnd 

 spot in a disc, or a star in the dark. Then, as the sun ascends, the 

 liglit rises higher till at last the wliole edge of the mountain will be 

 illuminated, while all the rest is in shade. We observe by looking 

 near the edge of this diagram that it is the shape of a cup or crater, 

 for that is tlie law of construction with the jnountains of the moon ; 

 and vou will see by the beautiful photograph of Mr. Kutherford's, 

 and also by another on the same scale, which Mr. Henry Draper has 

 executed of the old moon (this is the new moon, at the lirst quarter), 

 that the little mountain-tops, like islands in the dark, appear before 

 the rest is illuminated. Then the mountain shadows lengthen as the 

 sun o-oes down ; they point always in the direction opposite the sun ; 

 tliev point toward the north in the northern hemisphere, toward tlie 

 south in the southern hemisphere. Another shape is commonly that 

 of an enormous volcano; and, although you would not assert that 



