10 REPORT 1867. 



Brightness of the Whitish Spot. 



Since Schmidt suspected a change in Limie he has recorded nine compari- 

 sons of the brightness of Linne with that of the spot on the S.E. of Posi- 

 douius marked y by B. & M. (see ante, p. G). On seven occasions he found it 

 less bright than y, viz. on 1866, ^ox. 17, 19, 22, 23, and 2-1; and 1867, 

 Jan. 13 and 14 §. On Dec. 16, 1866, he recorded it equal to y ; and on Dec. 

 14, 1866, brighter than y. I also found it less bright than y on seven even- 

 ings, viz. 1866, Dec. 19, 1867, Jan. 14 §, 15, Feb. 11, May 11 and 15, and 

 Aug. 12. On May 17 and July 13 I recorded it as equal to y, and brighter than 

 y on March 14 and Aug. 10 ; on March 14 Mr. Buckingham estimated it as 

 equal to y. The above are comparisons -with y only, they give no informa- 

 tion as to the degree of brightness -n-ith which Linne reflected the sun's light. 

 The following are my estimations of the brightness of Linne, the scale being 

 shadow =0"^, the bright mountain in Aristarchus = 10°. 



1866, Dec. 14. 3-0 1867, Jan. 



,, lo. o'O ,, 



,, 18. o'o ,, 



„ 19. 5-0 July 



„ 21. 4-0 



These numbers appear to indicate that between 1866, Dec. 14, and 1867, 

 Aug. 12, Linne increased in brightness as the altitude of the sun increased. 



The following are estimations of the brightness of y Posidonius contempo- 

 raneous with those of Linne. 



o o 



1866, Dec. 19. 5-1 1867, July 8. 5-0 1867, Julv 13. 5-0 



„ 21. 4-5 „ 9. 5-0 Aug. 10. 3-9 



1867, Jan. 15. 5-5 „ 10. 5-0 „ 12. 6-2 



Observations were made on the evenings of Dec. IS and 19, 1866, with 



the view of confirming the estimations by comparison with other objects. 



They were as follows : — 



Dec. 18. Dee. 19. 



Proclus 9-0 9-0 



Censorinus .... 8-5 9-0 



Dionysius 8-0 8*5 . 



Conon 7-0 7-0 



Linne 5-5 5-0 



y Posidonius. ... 5-1 



Bessel 4-0 (ring) 4-5 



The similarity of appearance under high illumination exhibited by Linne 

 and y Posidonius [I E'^ ^'] is remarkable, especially as the two objects are so 

 very dissimilar in character. The white spot on the site of Linne, so far as 

 we know at present, differs, as we see it, very little, if any, in level from the 

 surrounding surface of the Mare Sennitatis. Most of the former records place 

 Linne on or very near a ridge crossing the Mare Serenitatis. Since October 

 16, 1866, the appearance of this ridge in the immediate neighhourhood of 

 Linne has not been recorded. On July 8, 1867, I have this note : — " The 

 ridge between Linne and Sulpicius Gallus quite perceptible, except a small 

 portion near Linne.'' This ridge is of variable height, the shadows distinct, 



§ Indicates that Schmidt's observation was contemporaneous with mine. — W. R. JB. 



i 



