1S6 Frof. Cleaveland^s descrijption of Halo s and Parhelia, 



A single Halo, or lumiaous circle, surrounding the sun, is, by 

 no means, an uncommon occurrence. Parhelia^ or luminous spots, 

 externally tinged with the colors of the rainbow, sometimes called 

 mocksuns, are also not unfrequently observed in the vicinity of the 

 true sun. But a collection of several Halos, both white and irised, 

 some of which form concentric circles, while others are tangential, 

 or intersect each other, accompanied also with several Parhelia, 

 both white and irised, is a phenomenon, which has been but rarely 

 observed. 



Among the most striking and beautiful exhibitions of this kind, 



r 



are those, which occurred at K-ome in 1639,' at Sedan in 1661, 

 and at Brunswick in iSid, 



There is, indeed, a general resemblance between these phe- 

 nomena, observed at different times, and in different places. But 

 there is also considerable diversity in the number, diameters, in- 

 clinations, and colors of the halos, and in the number, situation, 

 and colors of the parhelia. 



Were these striking phenomena more frequent, and their cause 

 better understood^ it would be unnecessary to increase the num- 

 her of descriptions. But, while we are still ignorant of the par- 

 ticular manner, in which Halos and Parhelia are produced, it 

 may be useful io collect additional facts, and preserve them on 

 record. Hereby the attention of Philosophers to this subject 

 may be renewed ; and, indeed, the slight modifications, which 

 these phenomena exhibit, may be extremely important in leading 

 to a correct explanation of the phenomena themselves, 



Bescartes, Gassendi, Dechales,Huyghens, Weidler, Muschen- 

 broeck, ^pinus and others have more or less devoted their atten- 

 tion to the investigation of Halos and Parhelia. All asree in at- 



tributing them to the refraction and reflection of light by particles 



