76 REPORT 1871. 



[The crater G is not seen in Bianchini's drawing of 1725, August 16, nor 

 in that illustrating his observations of 1727, August 23 and September 22. — 

 W. 11. B.] 



Mr. Pratt remarks, that in Short's observation of 1751, April 22, the first 

 streak of sunlight was on the upper part of the floor, followed soon after by 

 a parallel streak somewhat lower. " It is important," says Mr. Pratt, " to 

 learn what khid of telescope Short used during the observation ; for as he 

 was chiefly a maker of the Gregorian form, and as that construction does not 

 invert the image, it may be possible his term hwei- may mean southerly in- 

 stead of northerly, thus being in accord with modem observations." 



" The very interesting translation of Schroter's notes of 17b9, July 30, and 

 his discovery of something on the eastern half of floor, as if a kind of fer- 

 mentation was going on, and his discovery a few seconds later of an unveil- 

 ing or brightening, closely resembUng twihght, remind me," says Mr. Pratt, 

 " very forcibly of my own observations before mentioned. The half-shadows 

 of Schroter also remind me of what 1 have very often seen, as he describes ; 

 but 1 cannot understand his explanation of them. As far as I can see, half- 

 shadows presuppose an atmosphere ; and a well-authenticated course of ob- 

 servations of them would be good proof of the latter's presence." 



[If by the term " half-shadow" be meant the penumbral fringe of every 

 true shadow, the rays of light emerging from opposite limbs of the sun, 

 crossing beyond the object casting the shadow and then diverging, will fully 

 explain such a fringe. In the case of the sun rising above the mountains, 

 the reverse phenomenon occurs, viz. a gradual darkening fiinge skirting the 

 illuminated surface arising from less and less Hght arriving from the sun's 

 disk ; a true twilight is occasioned by the particles of an atmos^jheric medium 

 being illuminated by the sun's rays whUe the luminary is below the horizon, 

 and such I believe I have on several occasions witnessed. — W. E. B.] 



Interval 24 to 36 hours. 



1870, May 9. Mr. Gledhill describes spot Xo. 1 as easy ; a fine sharp 

 crater, with raised walls, much black shadow within, the east inner slope 

 bright : he also records 3 and 1 7 as presenting the same appearance as 

 No. 1. On October 3, at about IS"" earlier illumination, Mr. Gledhill did not 

 observe the crater character of these objects, but describes them as elevated 

 objects. This is remarkable, as on Oct. 3 the moon's latitude was 1° to 2° S., 

 whUe on May 9 it was 3° N., libration carrying Plato further from the eye, 

 yet the crater character was more distinct. Mr. Elger records No. 17 as seen 

 by ghmpses. 



As regards spots 13 and 19, the following remarks of Mr. Elger are inter- 

 esting : — '• The northern portion of the floor, including streak a, was noted 

 as equally hght ; the streak could not be traced." Mr. Gledhill writes, a not 

 to be distinguished from the bright floor all along the north border. Mr. 

 Elger found the same locahty " all light on the 10th." 



1870', February 9. Mr. Gledhill first saw spot No. 4, its bright W. Avail 

 only. He says, "This object seems to have loiver walls than 1, 17, or 3." 

 Mr. Gledhill writes : " For a few minutes I saw what appeared to be a very 

 low ridge running from N. to S. across the floor of Plato. It runs from the 

 N. border to spot 3, then curves to N^o. 1 , and again bends back to the E. 

 and reaches No. 17, and thence goes on to the S. border." [The low ridge 

 mentioned by Mr. Gledhill is, so far as I know, new. It is not coincident 

 with the great fault from N.W. to S.E. From a drawing subsequently sent 

 to me by Mr. Gledhill, it would indicate a fracture, having its origin at spot 



