446 Obscuration of a Lunar Crater. 



probable some valuable observations will result -from the 

 adoption of this course. 



P.S. Since the preceding was in type, we have received a 

 note from Mr. Birt, with the following additional information : — 



"Mr. Buckingham of Walworth, has obtained several photo- 

 graphs of the Moon, in October and November, which I have 

 examined. In almost all I find the place of ' Linne,' but the 

 object is very faint. I have one which he took on November 

 18, 1866, at 6-30 S.M.T. In this ' Linne' is visible, but its light 

 I estimate, by comparison with the ground around Copernicus, 

 to be only 2°. I have collected all the recorded brightnesses 

 and compared the photographs which I have in my possession. 

 The results are as follow : — 



" Variations of brilliancy of the crater c Linne/ since the 

 year 1788. 



Obssrvations. W.R.B. 



1788, Nov. 5. Schroter 0-5 8-125 



1823, May. 28. Lohrmann 7'0+ 



1831, Dec. 12, 13. B. and M. 6* 



Photographs. 



1858, Feb. 22. De la Rue 5- glass. 



1865, Oct. 4. „ „ 5- print. 



Rutherford 6* ,, 



1866, Nov. 18. Buckingham 2- „ 



" The above values for the photographs have been estimated, 

 and may be considered as a continuation of the series, W.R.B. ; 

 except Rutherford's, which is brighter than any degree of this 

 scale. There is some uncertainty in the determination of the 

 brightness on the prints, but the difference between 6° and 2° 

 is, I apprehend, too great to be attributed to differences aris- 

 ing in the printing. 



" The crater appears to have been brightest in 1823 ; Lohr- 

 mann always saw it brighter than Conon, which he records 

 at 7°-0. 



" From these records, it appears that Lohrmann and B. and 

 M. observed ' Linne ' to be brighter than any degree of the 

 scale you have — i. e., brighter than the surface around Kepler. 

 Schroter' s observations give about the eighth of a degree of my 

 scale ; but De la Rue's photographs give a brightness of about 

 that of the surface around Kepler ; and Rutherford's brighter — 

 probably the same as B. and M.'s. Buckingham's series is so 

 far accordant with Schmidt's observations as to indicate, very 

 strongly, that the crater has really undergone a change of somo 

 kind." 



