CHAP. 2. 19. RAINBOW, PARHELION, &c. 101 



are generally about 45 in diameter: in case of 

 double Halo, it might be worth while to take 

 the diameters of each of the concentric circles. 

 HALO TRIPLEX. Tres Annuli, in quorum 



centra communi Sol aut Luna appareat. 

 Triple Halones are extremely rare occur- 

 rences. 



HALO DISCOIDES. PI. VI. Fig. 3. Annulus 

 aream reliqud mibls parte lucidiorem con- 

 tinens, in cujus centra Luna aut Sol visus 

 est. 



A discoid Halo may be said to be a Halo 

 constituting the boundary of a large Corona: 

 it is generally of less diameter than usual, and 

 often coloured with the tints of the Iris. A 

 beautiful one appeared at Clapton on the 22d of 

 December, 1809, about midnight, during the 

 passage of a Wanecloud before the moon. 

 CORONA. PI. VI. Fig. 4. Discus lucidus, 

 vel portio circularis nubis reliqud lucidior, 

 in cujus centra Sol aut Luna videtur 

 When the sun or moon is seen through a 

 Jhin cloud, a portion of the cloud, more imme- 

 diately round the sun or moon, appears much 

 lighter than the rest of it : this luminous disk, 

 if I may be allowed the expression, I call a 

 Corona. 



