OBSERVATIONS OF LUNAR OBJECTS. 267 



tions differ among themselves. The point of intersection of the measured 

 streaks is in or near the locality of spot No. 19, at which a hrightness has 

 been observed. If the bright streaks are due to ejecta (see ante, p. 249), 

 their varying positions may not bo difficult of explanation. 



On September 13, 1870, the measures which determined the position of 

 streak a were as follows : — 



ti 

 end on border parallel to longest diameter 15 '3= Sid. 



On December 9 they were as follows : — 



For W. end on border parallel to longest diameter 16-1=-371. 



W. ,, „ transverse „ 4-5 = -104. 



„ E. „ „ longest „ 2-2 = -051. 



jj E. ,, „ transA-erse „ 1-1'7 = '339. 



These measures are more in accordance with two separate streaks, or there 

 may have heenfour streams of ejecta. 



As illustrative of the probable permanency of the streaks, at least for some 

 time, I quote the following from observations not included in the period 

 embraced by the discussion : — 



1871, October 22 ; interval 12 to 24 hours (?). — Mr. Elger noticed the 

 north-west portion of the floor as equally light ; and on November 27 he 

 recorded the sector, Pratt's streak p and y, as unusually easy ; a diagram is 

 given of a, AVebb's elbow, and a portion of c, agreeing with fig. 14, p. 284. 



1871, December 22, and following days. — Mr. Pratt noticed the haziness 

 over the north-west portion of the floor so frequently observed in April, May, 

 and June 1870. 



In the following pages the observations of streak a are arranged, first 

 chronologically, and second in the order of intervals from sunrise to sunset. 

 It is presumed that these arrangements, combined with the foregoing remarks, 

 will contribute to give a completeness to the history of a single feature closely 

 obseiwed during the greater portion of a period of two years. 



History op Streak a, OHRO^^oLOGicAiLr arranged. 



Period of the reoordecl appearance of a, 1869, Sept. 20, to 1871, March 3, 



The entire absence of this strealc from the floor of Plato during the period of 

 Mr. Pratfs observations in August 1869 is noteworthy. 



1869. " •■ 



Sept. 20, 168 to mer. The first record by Mr. Elger's drawing with the continu- 

 ation " 0." 



„ 25, 72 „ 60. Observations by Mr. Gledhill of the cm-vilinear streak from 

 spot No. 13 to the sector, also of " o." 



„ 27, 24 „ 12. « not seen, c described as a broad band of brightness. Width 

 J from spot No. 1 to rim. 

 Oct. 17, 108 „ 120. Well seen ; covers spots 13, 19, and 16 ; alignment, if pro- 

 duced, would cut N. border of B. & M.'s A. West " o." 



„ 19, 156 „ 168. Shown by Mr. GledhDl as a long narrow streak. Mr. Pratt 

 mentions a portion of the floor near the moimtain " m " 

 on the north of the streak as very dark. 



„ 21, 15G ,, 144. Brighter than on the 19th. 



„ 25, 60 „ 48. Dark space between the streak and border. 



„ 26, .36 „ 24. Seen bv Gledhill. 



„ 27, 12 „ 0. Seen by Gledhill. 



