76 A COMPARISON OF THE FEATURES OF THE EARTH AND THE MOON. 



century, been so greatly advanced that of the visible part of the moon we have 

 within the limits of telescopic vision much better maps than of most parts of the 

 earth, the classification of features and their nomenclature are in a very crude 

 shape. There is no sufficient categorizing of the various features, and the names 

 for them, generally suggested by misconceived analogies with terrestrial objects, 

 are often misleading. They serve, indeed, to perpetuate grave errors as to the 

 real nature of the lunar surface. Many of the most conspicuous topographic feat- 

 ures are unnamed, as, for instance, the promontories and capes along the shores 

 of the maria. Much of the nomenclature is so inwoven with our records that it 

 would be inadvisable to disturb it, but many changes and additions could be made 

 which would bring some order out of the confusion. I therefore venture to sug- 

 gest to selenographers that a committee should in some way be formed to under- 

 take a revision, or at least an extension, of the system of names applied to the 

 topography of the moon. 



As to further detailed work on the moon, it appears highly desirable that 

 small selected areas should be jointly studied and depicted by several well-trained 

 selenographers, the task being done in such a manner as will enable us to form a 

 judgment, first as to the effects of the personal equation of individual observers 

 in seeing and depicting lunar features, and second as to the effect of diverse con- 

 ditions of seeing, including the libration, on the aspects of lunar surface. In this 

 way we may hope to attain something like certainty concerning the occurrence 

 or non-occurrence of changes. 



It is also desirable that a close comparison be made between some of the 

 more ancient vulcanoids and those of evidently much newer age, as determined 

 by their relations to one another, and this with a view to ascertaining what are 

 the angles of slope of their respective ramparts and those buttress-like structures 

 which I have assumed to be flows of viscid lava. In this way we may possibly 

 obtain some idea as to the effect of the expansion and contraction due to solar 

 heat, or other forces upon their reliefs. 



A closer study as to the presence or absence of ash and other ejections of 

 fragmental materials than I have been able to make is desirable. I have given 

 reasons for believing that no such violent expulsion of broken-up lava, i. e., vol- 

 canic breccias or ash, took place in the eruptions of the vulcanoids ; but the 

 proof of this rests necessarily on negative evidence which requires much scrutiny. 

 This should be given to those cases where large well-developed craters lie adjacent 

 to older like structures. Where there is a honeycombed structure or old ram- 

 parts near such newer craters, the surface should be narrowly scanned to find if 

 the depressions have been filled with debris. 



The observation of Trouvelot, that the rills are sometimes continued beyond 

 their open fractures by light streaks, needs to be verified, for proof of such con- 

 dition would go far to show that some of these bands at least are due to the pas- 

 sage upward of vapors which congealed at their point of escape, and afford a fair 

 presumption that all of them are of this nature. This inquiry should be extended 

 so as to determine if any of the radiating streaks are coincident with distinct rills. 



