PLATE XIX. 



RAY SYSTEM ABOUT TYCHO. PHOTOGRAPHED BY RITCHEY. SCALE, THREE-EIGHTHS 



METER TO moon's DIAMETER. 



This, the most extensive of the ray systems of the moon, has its origin in the field about 

 Tycho, the large vulcanoid to which the numerous bands apparently converge. It appears under 

 the high sun as a large pit with a compound central cone. The rays of this system should be com- 

 pared with those which have their centers in Copernicus and Kepler. In these last named groups 

 the streaks are developed on relatively level ground, while on that of Tycho they intersect a rugged 

 surface. 



On the right hand, some of the bands may be seen crossing the Mare Nubium. Two of them 

 of great length are seen to be nearly parallel for a distance of some hundred miles. 



A number of large vulcanoids, partly in shadow, are shown on the southeast margin of the 

 moon. Of these the largest is Schiller. Its length, which is one hundred and twelve miles, will 

 serve as a scale in estimating that of the rays. 



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