DESCRIPTION OF PLATES. 



Tlie following plates have been selected with reference to the illustration of the questions 

 discussed in this memoir. The choice of illustrations has necessarily been limited to those features 

 of which it has been possible to procure good photographic negatives. On this account many 

 interesting structures are not pictured. As a whole, however, these delineations fairly present the 

 more important aspects of lunar topography as seen with good telescopes. 



In accordance with the usage of selenographers these plates are printed in the reversed order 

 in which they appear in a celestial telescope. The top of each is the south, the bottom the north, 

 the right hand the east, and the left the west. This will enable the student to compare them with 

 the maps of the moon. E.xcept when necessary for the immediate purposes of this memoir, the 

 structures depicted in the several plates are left unnamed. On many accounts this omission is to 

 be regretted, but an extended effort to designate by name the craters, mountains, etc., showed that 

 to accomplish this end it would be necessary to have key maps for the greater number of these 

 illustrations. If the student desires to determine the name of any of the more considerable 

 features, he can readily do so by comparing the plate with any of the good maps of the moon. 

 For this purpose the map of Elger is recommended. ' The photographic atlas of the moon by W. 

 H. Pickering, in the Annals of the Observatory of Harvard College, vol. li., 1903, and the same 

 work in a more popular form entitled " The Moon," by Doubleday, Page, & Co., N. Y., 1903, will 

 be found very useful for reference. Other reference would have been made to them in this work, 

 but they were published after the pages which precede this were put to press. 



In the description of each plate, attention is called to the more important features which it 

 depicts and occasionally to the place in the text where the matter is discussed. This arrangement 

 of necessity causes many rejietitions. It is hoped that the reader will find that the convenience of 

 the method compensates for this awkward mode of presentation, the aim being to provide in the 

 illustrations a basis for a criticism of the theories of lunar structure as near as possible to that 

 afforded by the use of a telescope. 



It is suggested that those who desire to spare their time in obtaining what value this memoir 

 may yield, should first read the text and then compare its statements with the facts presented in 

 the plates ; remembering that the matters of detail, such as those concerning the rills, the light 

 streaks, and the other more delicate features, can not yet effectively be rendered by photographs. 



' See The Moon, by Thos. Gwyn Elger. London. Geo. Philip & Son, 1895. The map is to be had separately 

 from the volume. « 



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