72 REPORT 1871. 



equator, E. loug., Mr. Elger records spots Nos. 1 and 17 in contiguity with 

 shadows of high peaks on west wall [y and ^] : Nos. 1, 3, 4 very plain [seen 

 also by Mr. Pratt], 17 faint, 25 only glimpsed, 7 suspected; no markings 

 seen. Mr. Pratt records on same day shadows of y, ?, and e on floor nearly 

 similar to 1809, Nov. 12, excepting that S showed a second point south of 

 chief one, and that of e did not exhibit a cleft. 



The importance of such careful observations as those which have furnished 

 the data for this interval cannot admit of question. The determination of 

 the epoch at which the floor first becomes illuminated, as compared with the 

 epoch of an easily computed phenomenon (sunrise at a given longitude on 

 the equator), places at once within our reach the means of ascertaining when 

 the appearances witnessed during the interval 10 to 24 hours after sunrise, 

 at 4° E. long, on the equator, 'rtU be repeated*. This is, however, a small 

 result compared with the forms and progressions of the shadows ; for by their 

 aid, especially if well sketched, and their lengths carefully measured, or even 

 estimated in parts of those of the three measured peaks y, I, and c, the dis- 

 tance of the west wall from the terminator being at the same time ascer- 

 tained, the irregularities of the west wall at sunrise, and by a similar process 

 those of the cast wall at sunset, may be obtained with tolerable precision by 

 13. & M.'s method described in ' Der Mond,' § 65, p. 98, and in the Keport 

 of the Lunar Committee of the British Association, ' Eeport,' 1867, p. 15. 

 We have thus the power, by multiplying such observations, of becoming inti- 

 mately acquainted with the breaks and gaps, the elevations and towering 

 pinnacles of the wall, and are in a position for handing down to our suc- 

 cessors details that may enable them to detect changes, if such should occur, 

 of sufficient magnitude to become perceptible. The shadows which I enu- 

 merated on Jan. 10, 1870, were six, — the longest y, one between y and ?, 

 I with its two peaks or saddle form, one south of e, and e. Mr. Joynson, of 

 Liverpool, gives in his drawing of the same date two peaks to ^. The irre- 

 gularities both of the floor and border have come out by these observations 

 with marked distinctness, and tend greatly to settle for the present epoch 

 the main features. If, however, changes are in progress, they may be, as on 

 the earth, extremely slow. 



The appearances recorded on January 10, 1870, being so different to that 

 witnessed by Bianchini, August 16, 1725, the following translation, by my 

 friend Mr. Kuott, from Bianchini's work ' Hesperi et Phosphori Nova Phe- 

 nomena' (Eomae, 1728), wUl doubtless be read with interest: — 



" Under the auspices of the Cardinal de Polignac, two large telescopes, 94 

 and 150 Boman palms long, by Campini, were prepared and erected, and on 

 the 16th of xlugust, 1725, the following observations of Plato were made. 



" Although on that night we were only able to turn the telescope 150 

 palms long, on the moon we detected, in the lunar spot named Plato, a 

 phenomenon not previously observed. The moon was at the time a little 

 past its first quadrature with the sun, which it had attained on the previous 

 day, and the spot Plato fell on the periphery of solar illumination, where is 

 the boundary of light and darkness in the lunar hemisphere exposed to the 

 sun. The whole of the very elevated margin, which on all sides surrounds 

 the spot like a deep pit, appeared bathed in the white rays of the sun. The 

 bottom of the spot, on the other hand, was stUl in darkness, the solar light 

 not yet reaching it ; but a track of ruddy light, like a beam, crossed the 



* Tlie longitudes of the terminator at 60° N. latitude on the equator, and at 60° S. lati- 

 tude, G reemi-ich, midnight, during the lunation, are given monthly in the ' Astronomical 

 Register.' 



