ON MAPPING THE SURFACE OF THE MOON. 239 



Appendix III. 



1st. Description of Map and Instructions for observing. 



2nd. A catalogue of objects photographed and observed in areas IV A" 

 and IV A^. 



3rd. The full-moon aspect of areas IV A* and IV A^. 



4th. A discussion of the lines of upheaval and depression in areas IV A" and 

 IV A^- 



British Association Outline* Map of the Moon, Zones II and IV, 

 Areas IV A" and IV A^. 



The present portions of the map include areas IV A*, IV A^ and parts of 

 IV A^^ and IV A'' ; they are in outline on a scale 200 inches, equal to the 

 moon's diameter. On these portions upwards of 200 objects are distinctly 

 specified, and, as indicated below, their relative degrees of visibility pointed 

 out. The scale of 200 inches to the moon's diameter appears to be the 

 smallest that can be used with advantage in the present state of selenography. 

 It allows every facility for inserting synonyms as well as various numerical 

 data, also for exhibiting with clearness the relative position of each object. 

 In some few instances objects, the precise nature of which is doubtful, are 

 inserted without a numerical reference, and some mentioned in the catalogue 

 are omitted, as their outhnes require careful determination. In the spaces 

 more or less blank there are small objects which await insertion when they 

 have been observed with adequate power, and their relative positions ascer- 

 tained. Without doubt much of the outline requires modrftcation, as it is 

 difficult to catch in the small intervals afforded for observation that correct- 

 ness in fonn and outline which is desirable, and instances of fine definition 

 in which it might be attained are rare, and occur at varying states of libra- 

 tion, and at different degrees of illuminating and visual angle : while, how- 

 ever, much may be achieved by the aid of photography, yet the evident relief 

 indicating heights and depths, and the diversity of light, shade, and shadow 

 interfere to no little extent in fomitng a judgment of the true outline, espe- 

 cially as no two photographs are Hkely to exhibit the same object under similar 

 circumstances ; still it is hoped the following catalogue of objects on areas 

 IV A" and IV A^, and the map will be mutually intelligible, and contribute to 

 a closer study of the moon's surface, if it be only to detect the errors in either. 



These portions of the map, as well as the accompanying catalogue, contain 

 all the known objects, 202 on an area of 50 superficial degrees, as shown 

 in existing photographs, and ascertained by personal observation. They are 

 issued with the twofold view of assisting observers in becoming acquainted 

 with the physical aspect, and also for enlarging the boundary of our know- 

 ledge of the moon's surfiice. They are printed red that observers may the 

 more readily insert additions and corrections in hlach. 



The basis of the map, as AveU as the principle upon which it is constructed, 

 is fully explained in the Report presented to the British Association at its 

 Meeting held in Nottingham, 1866 ; it may, however, be important to men- 

 tion that all positions, except those of the first order, are derived from Mr. 

 De la Rue's photograph of October 4, 1865, which was taken so near the 

 time of Mean Libration, that the coincidence of the Equator of the photo- 

 graph with that of the moon is sufficiently close to allow of direct mea- 



* This map is not intended to be a perfect or complete Lunar IVfap, but only a guide 

 to observers in obtaining data for the construction of a complete map. 



