OBSERVATIONS OF LUNAR OBJECTS. 67 



the tinted plate in the 'Student' of April 1870,. p. 161. The spots whose 

 positions have been determined by measures are Nos, 1, 4, 3, and 17. The 

 effect of the measures is to bring them eloser together and more towards the 

 centre of the crater than in the printed plans. On each occasion that the 

 measures were made, a diameter of the crater passing through spots Nos. 1 

 and 4, from A to B, was measured, also one at right angles to this from C 

 to D, passing through N"o. 1. All the remaining measures of spots and 

 streaks were referred to these diamet6;rs, spot No. 1 being the origin of 

 the coordinates, and the longest diameter being considered as unity. The 

 ratios of the means of the measvu'es were determined to be as follows : — 



Spot or Streak. 



Longest diameter A to B = 1000 No. 3 



„ 17 



Spofr No. 1 . Sector east end 



To east border B = -SIO „ west end 



„ west border A = -481 Both on border. 



southborder C ... = -309 Streak? -055 



north border D ... = -309 „ e 



spot No. 4 = -182 „ base on A B . . 



Streak a W. end . . 



„ a E. end ... 

 „ /3 on border 



In order to plot the spots that have been laid down by alignment and 

 estimation, it is necessary to aUgn \vith the measured spots, and particularly 

 with objects on the border, a process that will be adopted in the preparation 

 or a monogram of Plato. 



APPENDIX. 



Obseetees' Notes. 



These are arranged in each interval of 12 hours according to season, so as 

 to give increasing altitudes of the sun from ©—53 =270°. Winter in the 

 northern hemisphere. 



Interval to 12 hours. 



1869, Oct. 13, 7'> (O- S =76°24'-8, Oct. 12^ 21*^).— Ten hours after the 

 epoch of sunrise at the equator in E. long. 4° ©'•6, the first streak of sun- 

 light was seen by Mr. Gledhill to faU on the floor of Plato through the gap 

 in the west wall between B. & M.'s peaks S and e, the W. extremity lying 

 on or near the fault from N.W. to S.E., and bringing into visibility the cra- 

 terlet No. 3, which is seen earliest of all the spots. Mr. Gledhill gives the 

 sun's azimuth equal to 87° 31', the altitude being equal to the angle formed 

 by the height of the depression in the wall between the peaks above the 

 point of the floor on which the sun's rays first impinge. 



Interval 12 to 24 hours. 



1870, July 6, 8''. — Twelve hours and a half after epoch of sunrise at the 

 equator, E. long. 4° ll'^o, 0- Q , July 5, 19, 30 = 354° 54'^4. Mr. Gledhill 

 again witnessed the first streak of sunlight fall on the floor of Plato, and 

 observed spot No. 3 just within it, and remarked that the streak lay parallel 

 with the longest diameter, and did not incline from No. 3 as it did in January. 

 [On the 13th of October, 1869, at 7", Mr. Gledhill remarked that the streak 

 was a little inclined to the N., and not quite parallel with the rim.] At 9*^ 

 of July 6, 1870, Mr. Gledhill remarked that a line through the two gaps or 



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