ON MAPPING THE SURFACE OF THE MOON. 219 



The four areas I Y A", TV A/3, lY X'i, and IV A 'J are characterized by sevc- 

 rd faults; the particulars of those- in IV A* and IV A ^ will be found in Ap- 

 pendix III. 



In the Eeport presented at Bii-mingham, allusion A^as made to the measure- 

 ment of the diameters of craters for the determination of magnitude. It is 

 worthy of remark that measures have been taken of some of the larger craters 

 inserted in areas IVA/^ and IV A*?, and upon comparison these measures have 

 been found to agree nearly with those taken from the photograph. 



During the past year Herr Schmidt, of Athens, has issued a catalogue of 

 425 rills ; 278 of these have been discovered by himself. They consist of 

 rills, crater-rills, crater-rows, and valleys with some faults. In the cata- 

 logiie of objects on area IV A^, which forms part of Appendix III., are ei"ht 

 not to be found in his printed catalogue. Four of these have been disco- 

 vered since July 20, 1866. The great fault crossing the area from Tycho is 

 not included. 



The number of series of observations of the moon's surface as described in 

 the last Eeport (Report, 1865, p. 303), now amount to 490. The progress of 

 the actual work as regards the registration of the objects observed, and others 

 of a conspicuous character on the moon's surface during the past year, is 

 shown in the following digest. 



At the Bath Meeting 386 objects were symbolized and registered ; at the 

 Birmingham Meeting 785 ; and at the jN'ottingham Meeting 1321 ; of these 

 536 were symbolized and registered in the fifty weeks betM-cen the Meetings 

 of the Association at Birmingham and Nottingham. 



The 1321 objects are disposed over the moon's surface as follows : — 



396 on 70 areas in Quadrant I. 



346 „ 86 „ „ „ II. 



163 „ 53 „ „ „ III. 



416 „ 62 „ „ „ IV. 



Total 1321 271 areas* on the moon's surface. 



Previous to the Meeting at Birmingham, the regions and groups that 

 had been the subjects of special observation were : — On Quadrant I. the rill 

 system of Triesnecker ; the great riU of Ariadaeus ; the Plain of Dionysius ; 

 the walled formation Posidonius, and the Mare Crisium, especially the craters 

 on its surface. (See Ptcport, 1865, pp. 292, 293.) On Quadrant II. the 

 Teneriffe Mountains, Plato, and its neighbourhood, and the valley J. J. 

 Cassini. On Quadrant III. the walled plain Gassendi, and the tableland 

 " Terra Photographica " (De La Rue). 



The extension of the Register by the addition of 536 objects during the 

 past year, has reference, first, to the symbolization of points of the first 

 order. Beer and Miidlcr have expi-essed these points in their Hst — which I 

 have of course followed — too vaguely, and it requires some searching in the 

 topographical part of ' Dor Mond ' to find the exact object intended. By 

 appending the symbol, as I have done in Appendix I., when the Register is 

 sufficiently advanced for publication in a consecutive from, the identification 

 of each point will be easy. Second, the mapping out of the areas IVA", 

 IVA/5, IVAT',_IVA^, IVA'', and IVA^, has necessarily involved the symboliza- 

 tion of the objects on this part of the moon, so that to the above-named regions 

 that of Hipparchus and its neighboui-hood may now be added. 



* The reader -will find a description and symbolization of these areas in the Eeport of 

 the Lunar Committee presented at Birmingham. (Eeport, 1865, p. 287 et seq.) 



