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VIII. On a Paraselene witnessed on May 6tk 3 1841. By 

 W. R. Birt, Esq., Librarian and Assistant Secretary to the 

 Metropolitan Institution. 



To E. W. Brayley, Jun., Esq. 



My dear Sir, 



I HAD an opportunity last night of witnessing an interesting 

 exhibition of paraselene. The halo occurred in a modifi- 

 cation of cirro-stratus, which I have termed nebula suspensa, 

 in order to distinguish it from other varieties of cirro-stratus. 

 I believe it is the only variety that exhibits halos ; I do not re- 

 collect at the moment having observed them in others. One 

 half only of the halo was visible, the moon being low at the 

 time of observation ; this half exhibited three portions, which 

 were more strongly illuminated than the rest of the semicircle. 

 The inclosed rough sketch will convey some idea of the posi- 

 tion of these illuminated portions ; the semicircle was very 

 distinct, the base or the diameter joining the two extremities 

 and passing through the moon, being parallel with the hori- 

 zon. Both these extremities were strongly illuminated as com- 

 pared with the semicircle generally, but faint as compared 

 with the moon ; these illuminated portions were not well de- 

 fined ; their appearance did not convey to me the idea of their 

 being images of the moon, but merely portions of the halo 

 more strongly illuminated than the rest. Perhaps this little 

 figure will give the best idea of their appearance. 



* Mars. 



East. m % ^ ^Bk WesL 



Jupiter. M. 

 The darkened portions represent the illuminated portions of the semicircle. 



The illuminated portion at the summit of the semicircle was 

 very interesting ; it was fainter than the portions above men- 

 tioned, and filled a small segment of the halo, in the same 

 manner as a pencil of rays, diverging from a luminous point, 

 would illuminate the segment of a ring situated within its cone. 

 This illuminated portion appeared somewhat of a lozenge 

 form, having the part immediately over the moon brightest 

 and broadest; it became gradually fainter and narrower to- 

 wards its eastern and western extremities. The difference 

 between it and the illuminated extremities of the semicircle 

 was very distinct. 



