240 KEPOKT— 1866. 



sures of every object on the photograph. In the case of the first meridian, 

 a small correction has been applied. The points of the first order, which 

 are most scrupulously regarded, are found in Appendix I. of the above- 

 named Keport. In laying down those in quadrant IV., the greatest error 

 discovered in checking them amounted only to -0008, the moon's semi- 

 diameter being equal to unity. 



The following abbreviations are employed on the Map. 

 The Arabic numerals, except in cases of measiu-ement, refer to the area of 

 twenty -five superficial degrees indicated — and in quoting to be preceded — 

 by the symbol of the area (see Brit. Assoc. Report, 1865, p. 288). 



The small Greek letters refer to the same objects indicated by them on 

 Beer and Madler's Map of 37 inches diameter. The Roman capitals and 

 small letters preceded by B. & M. are of similar import. 



Points of the first order. 

 X Points of the second order. 



o Craters, 



w Depressions. 



A Mountains. 



N.B. The arrow-head 18 1 Y Y^ ^^^■- i ■, n • 



directed towards the V | Mountam slopes and Valley sides, 



lowest point. J ** Very conspicuous objccts. 



* Easy objects. 



t Difficult objects. 



J Objects rarely visible. 



B. & M. Beer and Madler. 



L. S. Lohrmann's Sections. 



L. M. Lohrmann's Map. 



S. R. Schmidt's RiUs. 



Eng. ft. EngHsh feet. 



Metres. 



Dotted lines in some instances indicate the bases of mountains, the crests 

 being shown by continuous lines, also the lowest parts of valleys ; in others 

 the interior feet of crater slopes as in HaUey, where the dotted line points 

 out the base of the interior E. slope, in others lucid markings or streaks 

 which require further observation. 



Some attempt has been made to indicate differences of level by inscribing 

 on the map the words " high level," " higher level," " lower level," and " low 

 level ;" thus the level S. of HaUey is very much higher than that of the floor 

 of Hipparchus N. of HaUey, and that of Albategnius marked "low level" is 

 the lowest ; the words higher and lower being comparative bettveen high and 

 low. This difference of level is brought out in a very marked manner by an 

 oblique illumination. 



The space between every 5° of latitude north and south constitutes a 

 zone numbered from I. to XXXVI. (see Report, 1865, pp. 288-290). 

 For the employment of the map, each zone may be divided into five sub- 

 zones of 1° ; and if to every observer tivo were allotted, so that half of the 

 area selected by each were to overlap half of the adjoining areas of two sub- 

 zones, observations, additions, and corrections will be received from two in- 

 dependent observers. As it is very probable that in some instances ob- 

 servers may have but little previous acquaintance either with the aspect of 

 the moon's surface as regards " detail " or with methods of observation, 

 the following instructions for observing the objects, also for correcting and 

 adding to the map and catalogue, are drawn up upon this probability. The 



