ON MAPPING THE SURFACE OF THE MOON. 269 



streak not unlike a " ray," extending from IV A^ ^^ (a bright spot), crossing 

 jY^?48^ where it becomes brighter than usual, still further crossing the 

 crater-row east of IVA^^, and proceeding to the high mountain IV A^''' 

 on the west border of Ptolemseus, has been identified with a portion of a line 

 of disturbance from Tycho. The group IV A^ ' , IV A^ '^, IV A^ ^, and IV A^ '' 

 is also bright. It is worthy of remark that the general direction of these 

 light and dark spaces is towards Tycho. 



Areas IV A«, IV A^, 

 Directions of EiUs, Crater-rills, Crater-roivs, Valleys, Mountain-chains, ^"c. 



Since the year 1786 several endeavours have been made to render certain 

 featm-es of the moon's surface especial objects of study, particularly the rills, 

 the first of which— the remarkable wedge-shaped valley of the Alps — was 

 discovered by Bianchini on Sept. 22, 1727*. Lohrmann, Miidler, Kinau, and 

 Schmidt have carried on the study of rills during the interim, and the number 

 now known exceeds 425. In the admirable ' Catalogue of Eills ' lately published 

 by Schmidt, not only has the class been considerably augmciited by including 

 large valleys, of which the first- discovered rill may be regarded as the type, 

 but the dii-ection of each has been given in a very clear and distinct manner. 

 I am not aware, however, that any attempt has been made to classify the 

 " rills " according to direction, which may have an important bearing on the 

 subject of the manifestation of the effects of those forces which have modified 

 the surface ; for there can be no doubt that while the crater-form is appa- 

 rently by far the most prominent feature, the directions of the rills, valleys, 

 crater-rows, and mountain-chains indicate the lines in which the forces mo- 

 difying the surface operated, it may be over wide-spread areas around foci 

 of disturbance, such as Tycho, and other ray-centres; consequently an arrange- 

 ment of these directions may in some degree contribute to our knowledge of 

 the operation of forces on a minor scale which may have modified the features 

 of smaller portions of the surface. 



It IS not my intention to imdertake a classification of the directions of 

 Schmidt's 425 riUs, but simply, as this work proceeds, to arrange under each 

 artificial area of 5° of longitude by 5° of latitude the directions of rills, cra- 

 ter-rows, crater-rills, vaUeys, mountain-chains, or any feature that indicates 

 the line in which the action of either upheaving or depressing forces has been 

 manifested, thus laying the foundation of a more enlarged generalization at 

 some future period. 



In the following Table of lines of upheaval and depression in areas IV A" 

 and IV A^ the directions are expressed by the two opposite points of the 

 lunar compass between which the line lies, regarding throughout the meridian 

 as the starting line, and passing from south by west to north. In Qua- 

 drants I. and IV. the arrangement will be from the meridian westward, and 

 m Quadrants II. and III. from the meridian eastward. 



* Schmidt, in his ; Catalogue of Kills', ascribes the discovery of this interesting formation 

 to ScLroter, who noticed it 1787, October 1, and delineated it in his Selenotopograpliische 

 l-ragmente; but it was carefully observed by Bianchini on the date given in the te^t, and 

 described and figured by Inn. in his ' Hesperi et Phosphori Nova Phtenomena,' printed at 

 itome in lilii. Eianchini mentions it as indicated in Cassini's chart. 



